fish-shell/parse_execution.cpp

/**\file parse_execution.cpp

   Provides the "linkage" between a parse_node_tree_t and actual execution structures (job_t, etc.)

   A note on error handling: fish has two kind of errors, fatal parse errors non-fatal runtime errors. A fatal error prevents execution of the entire file, while a non-fatal error skips that job.

   Non-fatal errors are printed as soon as they are encountered; otherwise you would have to wait for the execution to finish to see them.
*/

#include "parse_execution.h"
#include "parse_util.h"
#include "complete.h"
#include "wildcard.h"
#include "builtin.h"
#include "parser.h"
#include "expand.h"
#include "reader.h"
#include "wutil.h"
#include "exec.h"
#include "path.h"
#include <algorithm>

/* These are the specific statement types that support redirections */
static bool specific_statement_type_is_redirectable_block(const parse_node_t &node)
{
    return node.type == symbol_block_statement || node.type == symbol_if_statement || node.type == symbol_switch_statement;

}

parse_execution_context_t::parse_execution_context_t(const parse_node_tree_t &t, const wcstring &s, parser_t *p) : tree(t), src(s), parser(p), eval_level(0)
{
}

/* Utilities */

wcstring parse_execution_context_t::get_source(const parse_node_t &node) const
{
    return node.get_source(this->src);
}

const parse_node_t *parse_execution_context_t::get_child(const parse_node_t &parent, node_offset_t which, parse_token_type_t expected_type) const
{
    return this->tree.get_child(parent, which, expected_type);
}

node_offset_t parse_execution_context_t::get_offset(const parse_node_t &node) const
{
    /* Get the offset of a node via pointer arithmetic, very hackish */
    const parse_node_t *addr = &node;
    const parse_node_t *base = &this->tree.at(0);
    assert(addr >= base);
    node_offset_t offset = addr - base;
    assert(offset < this->tree.size());
    assert(&tree.at(offset) == &node);
    return offset;
}

const parse_node_t *parse_execution_context_t::infinite_recursive_statement_in_job_list(const parse_node_t &job_list, wcstring *out_func_name) const
{
    assert(job_list.type == symbol_job_list);
    /*
      This is a bit fragile. It is a test to see if we are
      inside of function call, but not inside a block in that
      function call. If, in the future, the rules for what
      block scopes are pushed on function invocation changes,
      then this check will break.
    */
    const block_t *current = parser->block_at_index(0), *parent = parser->block_at_index(1);
    bool is_within_function_call = (current && parent && current->type() == TOP && parent->type() == FUNCTION_CALL);
    if (! is_within_function_call)
    {
        return NULL;
    }

    /* Check to see which function call is forbidden */
    if (parser->forbidden_function.empty())
    {
        return NULL;
    }
    const wcstring &forbidden_function_name = parser->forbidden_function.back();

    /* Get the first job in the job list. */
    const parse_node_t *first_job = tree.next_node_in_node_list(job_list, symbol_job, NULL);
    if (first_job == NULL)
    {
        return NULL;
    }

    /* Here's the statement node we find that's infinite recursive */
    const parse_node_t *infinite_recursive_statement = NULL;

    /* Get the list of statements */
    const parse_node_tree_t::parse_node_list_t statements = tree.specific_statements_for_job(*first_job);

    /* Find all the decorated statements. We are interested in statements with no decoration (i.e. not command, not builtin) whose command expands to the forbidden function */
    for (size_t i=0; i < statements.size(); i++)
    {
        /* We only care about decorated statements, not while statements, etc. */
        const parse_node_t &statement = *statements.at(i);
        if (statement.type != symbol_decorated_statement)
        {
            continue;
        }

        const parse_node_t &plain_statement = tree.find_child(statement, symbol_plain_statement);
        if (tree.decoration_for_plain_statement(plain_statement) != parse_statement_decoration_none)
        {
            /* This statement has a decoration like 'builtin' or 'command', and therefore is not infinite recursion. In particular this is what enables 'wrapper functions' */
            continue;
        }

        /* Ok, this is an undecorated plain statement. Get and expand its command */
        wcstring cmd;
        tree.command_for_plain_statement(plain_statement, src, &cmd);
        expand_one(cmd, EXPAND_SKIP_CMDSUBST | EXPAND_SKIP_VARIABLES);

        if (cmd == forbidden_function_name)
        {
            /* This is it */
            infinite_recursive_statement = &statement;
            if (out_func_name != NULL)
            {
                *out_func_name = forbidden_function_name;
            }
            break;
        }
    }

    assert(infinite_recursive_statement == NULL || infinite_recursive_statement->type == symbol_decorated_statement);
    return infinite_recursive_statement;
}

enum process_type_t parse_execution_context_t::process_type_for_command(const parse_node_t &plain_statement, const wcstring &cmd) const
{
    assert(plain_statement.type == symbol_plain_statement);
    enum process_type_t process_type = EXTERNAL;

    /* Determine the process type, which depends on the statement decoration (command, builtin, etc) */
    enum parse_statement_decoration_t decoration = tree.decoration_for_plain_statement(plain_statement);

    /* Do the "exec hack" */
    if (decoration != parse_statement_decoration_command && cmd == L"exec")
    {
        /* Either 'builtin exec' or just plain 'exec', and definitely not 'command exec'. Note we don't allow overriding exec with a function. */
        process_type = INTERNAL_EXEC;
    }
    else if (decoration == parse_statement_decoration_command)
    {
        /* Always a command */
        process_type = EXTERNAL;
    }
    else if (decoration == parse_statement_decoration_builtin)
    {
        /* What happens if this builtin is not valid? */
        process_type = INTERNAL_BUILTIN;
    }
    else if (function_exists(cmd))
    {
        process_type = INTERNAL_FUNCTION;
    }
    else if (builtin_exists(cmd))
    {
        process_type = INTERNAL_BUILTIN;
    }
    else
    {
        process_type = EXTERNAL;
    }
    return process_type;
}

bool parse_execution_context_t::should_cancel_execution(const block_t *block) const
{
    return cancellation_reason(block) != execution_cancellation_none;
}

parse_execution_context_t::execution_cancellation_reason_t parse_execution_context_t::cancellation_reason(const block_t *block) const
{
    if (shell_is_exiting())
    {
        return execution_cancellation_exit;
    }
    else if (parser && parser->cancellation_requested)
    {
        return execution_cancellation_skip;
    }
    else if (block && block->loop_status != LOOP_NORMAL)
    {
        /* Nasty hack - break and continue set the 'skip' flag as well as the loop status flag. */
        return execution_cancellation_loop_control;
    }
    else if (block && block->skip)
    {
        return execution_cancellation_skip;
    }
    else
    {
        return execution_cancellation_none;
    }
}

/* Return whether the job contains a single statement, of block type, with no redirections */
bool parse_execution_context_t::job_is_simple_block(const parse_node_t &job_node) const
{
    assert(job_node.type == symbol_job);

    /* Must have one statement */
    const parse_node_t &statement = *get_child(job_node, 0, symbol_statement);
    const parse_node_t &specific_statement = *get_child(statement, 0);
    if (! specific_statement_type_is_redirectable_block(specific_statement))
    {
        /* Not an appropriate block type */
        return false;
    }


    /* Must be no pipes */
    const parse_node_t &continuation = *get_child(job_node, 1, symbol_job_continuation);
    if (continuation.child_count > 0)
    {
        /* Multiple statements in this job, so there's pipes involved */
        return false;
    }

    /* Check for arguments and redirections. All of the above types have an arguments / redirections list. It must be empty. */
    const parse_node_t &args_and_redirections = tree.find_child(specific_statement, symbol_arguments_or_redirections_list);
    if (args_and_redirections.child_count > 0)
    {
        /* Non-empty, we have an argument or redirection */
        return false;
    }

    /* Ok, we are a simple block! */
    return true;
}

parse_execution_result_t parse_execution_context_t::run_if_statement(const parse_node_t &statement)
{
    assert(statement.type == symbol_if_statement);

    /* Push an if block */
    if_block_t *ib = new if_block_t();
    ib->node_offset = this->get_offset(statement);
    parser->push_block(ib);

    parse_execution_result_t result = parse_execution_success;

    /* We have a sequence of if clauses, with a final else, resulting in a single job list that we execute */
    const parse_node_t *job_list_to_execute = NULL;
    const parse_node_t *if_clause = get_child(statement, 0, symbol_if_clause);
    const parse_node_t *else_clause = get_child(statement, 1, symbol_else_clause);
    for (;;)
    {
        if (should_cancel_execution(ib))
        {
            result = parse_execution_cancelled;
            break;
        }

        assert(if_clause != NULL && else_clause != NULL);
        const parse_node_t &condition = *get_child(*if_clause, 1, symbol_job);

        /* Check the condition. We treat parse_execution_errored here as failure, in accordance with historic behavior */
        parse_execution_result_t cond_ret = run_1_job(condition, ib);
        bool take_branch = (cond_ret == parse_execution_success) && proc_get_last_status() == EXIT_SUCCESS;

        if (take_branch)
        {
            /* condition succeeded */
            job_list_to_execute = get_child(*if_clause, 3, symbol_job_list);
            break;
        }
        else if (else_clause->child_count == 0)
        {
            /* 'if' condition failed, no else clause, we're done */
            job_list_to_execute = NULL;
            break;
        }
        else
        {
            /* We have an 'else continuation' (either else-if or else) */
            const parse_node_t &else_cont = *get_child(*else_clause, 1, symbol_else_continuation);
            assert(else_cont.production_idx < 2);
            if (else_cont.production_idx == 0)
            {
                /* it's an 'else if', go to the next one */
                if_clause = get_child(else_cont, 0, symbol_if_clause);
                else_clause = get_child(else_cont, 1, symbol_else_clause);
            }
            else
            {
                /* it's the final 'else', we're done */
                assert(else_cont.production_idx == 1);
                job_list_to_execute = get_child(else_cont, 1, symbol_job_list);
                break;
            }
        }
    }

    /* Execute any job list we got */
    if (job_list_to_execute != NULL)
    {
        run_job_list(*job_list_to_execute, ib);
    }

    /* Done */
    parser->pop_block(ib);

    return result;
}

parse_execution_result_t parse_execution_context_t::run_begin_statement(const parse_node_t &header, const parse_node_t &contents)
{
    assert(header.type == symbol_begin_header);
    assert(contents.type == symbol_job_list);

    /* Basic begin/end block. Push a scope block. */
    scope_block_t *sb = new scope_block_t(BEGIN);
    parser->push_block(sb);

    /* Run the job list */
    parse_execution_result_t ret = run_job_list(contents, sb);

    /* Pop the block */
    parser->pop_block(sb);

    return ret;
}

/* Define a function */
parse_execution_result_t parse_execution_context_t::run_function_statement(const parse_node_t &header, const parse_node_t &contents)
{
    assert(header.type == symbol_function_header);
    assert(contents.type == symbol_job_list);
    parse_execution_result_t result = parse_execution_success;

    /* Get arguments */
    const parse_node_t *unmatched_wildcard = NULL;
    wcstring_list_t argument_list = this->determine_arguments(header, &unmatched_wildcard);

    if (unmatched_wildcard != NULL)
    {
        report_unmatched_wildcard_error(*unmatched_wildcard);
        result = parse_execution_errored;
    }

    if (result == parse_execution_success)
    {
        const wcstring contents_str = get_source(contents);
        wcstring error_str;
        int err = define_function(*parser, argument_list, contents_str, &error_str);
        proc_set_last_status(err);

        if (! error_str.empty())
        {
            this->report_error(header, L"%ls", error_str.c_str());
            result = parse_execution_errored;
        }
    }
    return result;

}

parse_execution_result_t parse_execution_context_t::run_block_statement(const parse_node_t &statement)
{
    assert(statement.type == symbol_block_statement);

    const parse_node_t &block_header = *get_child(statement, 0, symbol_block_header); //block header
    const parse_node_t &header = *get_child(block_header, 0); //specific header type (e.g. for loop)
    const parse_node_t &contents = *get_child(statement, 2, symbol_job_list); //block contents

    parse_execution_result_t ret = parse_execution_success;
    switch (header.type)
    {
        case symbol_for_header:
            ret = run_for_statement(header, contents);
            break;

        case symbol_while_header:
            ret = run_while_statement(header, contents);
            break;

        case symbol_function_header:
            ret = run_function_statement(header, contents);
            break;

        case symbol_begin_header:
            ret = run_begin_statement(header, contents);
            break;

        default:
            fprintf(stderr, "Unexpected block header: %ls\n", header.describe().c_str());
            PARSER_DIE();
            break;
    }

    return ret;
}

parse_execution_result_t parse_execution_context_t::run_for_statement(const parse_node_t &header, const parse_node_t &block_contents)
{
    assert(header.type == symbol_for_header);
    assert(block_contents.type == symbol_job_list);

    /* Get the variable name: `for var_name in ...` */
    const parse_node_t &var_name_node = *get_child(header, 1, parse_token_type_string);
    const wcstring for_var_name = get_source(var_name_node);

    /* Get the contents to iterate over. */
    const parse_node_t *unmatched_wildcard = NULL;
    wcstring_list_t argument_list = this->determine_arguments(header, &unmatched_wildcard);
    if (unmatched_wildcard != NULL)
    {
        return report_unmatched_wildcard_error(*unmatched_wildcard);
    }

    parse_execution_result_t ret = parse_execution_success;

    for_block_t *fb = new for_block_t(for_var_name);
    parser->push_block(fb);

    /* Note that we store the sequence of values in opposite order */
    std::reverse(argument_list.begin(), argument_list.end());
    fb->sequence = argument_list;

    /* Now drive the for loop. */
    while (! fb->sequence.empty())
    {
        if (should_cancel_execution(fb))
        {
            ret = parse_execution_cancelled;
            break;
        }

        const wcstring &for_variable = fb->variable;
        const wcstring &val = fb->sequence.back();
        env_set(for_variable, val.c_str(),  ENV_LOCAL);
        fb->sequence.pop_back();
        fb->loop_status = LOOP_NORMAL;
        fb->skip = 0;

        this->run_job_list(block_contents, fb);

        if (this->cancellation_reason(fb) == execution_cancellation_loop_control)
        {
            /* Handle break or continue */
            if (fb->loop_status == LOOP_CONTINUE)
            {
                /* Reset the loop state */
                fb->loop_status = LOOP_NORMAL;
                fb->skip = false;
                continue;
            }
            else if (fb->loop_status == LOOP_BREAK)
            {
                break;
            }
        }
    }

    parser->pop_block(fb);

    return ret;
}


parse_execution_result_t parse_execution_context_t::run_switch_statement(const parse_node_t &statement)
{
    assert(statement.type == symbol_switch_statement);
    parse_execution_result_t ret = parse_execution_success;
    const parse_node_t *matching_case_item = NULL;

    parse_execution_result_t result = parse_execution_success;

    /* Get the switch variable */
    const parse_node_t &switch_value_node = *get_child(statement, 1, parse_token_type_string);
    const wcstring switch_value = get_source(switch_value_node);

    /* Expand it */
    std::vector<completion_t> switch_values_expanded;
    int expand_ret = expand_string(switch_value, switch_values_expanded, EXPAND_NO_DESCRIPTIONS);
    switch (expand_ret)
    {
        case EXPAND_ERROR:
        {
            result = report_error(switch_value_node,
                                  _(L"Could not expand string '%ls'"),
                                  switch_value.c_str());
            break;
        }

        case EXPAND_WILDCARD_NO_MATCH:
        {
            /* Store the node that failed to expand */
            report_error(switch_value_node, WILDCARD_ERR_MSG, switch_value.c_str());
            ret = parse_execution_errored;
            break;
        }

        case EXPAND_WILDCARD_MATCH:
        case EXPAND_OK:
        {
            break;
        }
    }

    if (result == parse_execution_success && switch_values_expanded.size() != 1)
    {
        result = report_error(switch_value_node,
                              _(L"switch: Expected exactly one argument, got %lu\n"),
                              switch_values_expanded.size());
    }
    const wcstring &switch_value_expanded = switch_values_expanded.at(0).completion;

    switch_block_t *sb = new switch_block_t(switch_value_expanded);
    parser->push_block(sb);

    if (result == parse_execution_success)
    {
        /* Expand case statements */
        const parse_node_t *case_item_list = get_child(statement, 3, symbol_case_item_list);

        /* Loop while we don't have a match but do have more of the list */
        while (matching_case_item == NULL && case_item_list != NULL)
        {
            if (should_cancel_execution(sb))
            {
                result = parse_execution_cancelled;
                break;
            }

            /* Get the next item and the remainder of the list */
            const parse_node_t *case_item = tree.next_node_in_node_list(*case_item_list, symbol_case_item, &case_item_list);
            if (case_item == NULL)
            {
                /* No more items */
                break;
            }

            /* Pull out the argument list */
            const parse_node_t &arg_list = *get_child(*case_item, 1, symbol_argument_list);

            /* Expand arguments. We explicitly ignore unmatched_wildcard. That is, a case item list may have a wildcard that fails to expand to anything. */
            const wcstring_list_t case_args = this->determine_arguments(arg_list, NULL);

            for (size_t i=0; i < case_args.size(); i++)
            {
                const wcstring &arg = case_args.at(i);

                /* Unescape wildcards so they can be expanded again */
                wchar_t *unescaped_arg = parse_util_unescape_wildcards(arg.c_str());
                bool match = wildcard_match(switch_value_expanded, unescaped_arg);
                free(unescaped_arg);

                /* If this matched, we're done */
                if (match)
                {
                    matching_case_item = case_item;
                    break;
                }
            }
        }
    }

    if (result == parse_execution_success && matching_case_item != NULL)
    {
        /* Success, evaluate the job list */
        const parse_node_t *job_list = get_child(*matching_case_item, 3, symbol_job_list);
        result = this->run_job_list(*job_list, sb);
    }

    parser->pop_block(sb);

    return result;
}

parse_execution_result_t parse_execution_context_t::run_while_statement(const parse_node_t &header, const parse_node_t &block_contents)
{
    assert(header.type == symbol_while_header);
    assert(block_contents.type == symbol_job_list);

    /* Push a while block */
    while_block_t *wb = new while_block_t();
    wb->status = WHILE_TEST_FIRST;
    wb->node_offset = this->get_offset(header);
    parser->push_block(wb);

    parse_execution_result_t ret = parse_execution_success;

    /* The condition and contents of the while loop, as a job and job list respectively */
    const parse_node_t &while_condition = *get_child(header, 1, symbol_job);

    /* Run while the condition is true */
    for (;;)
    {
        /* Check the condition */
        parse_execution_result_t cond_result = this->run_1_job(while_condition, wb);

        /* We only continue on successful execution and EXIT_SUCCESS */
        if (cond_result != parse_execution_success || proc_get_last_status() != EXIT_SUCCESS)
        {
            break;
        }

        /* Check cancellation */
        if (this->should_cancel_execution(wb))
        {
            ret = parse_execution_cancelled;
            break;
        }


        /* The block ought to go inside the loop (see #1212) */
        this->run_job_list(block_contents, wb);

        if (this->cancellation_reason(wb) == execution_cancellation_loop_control)
        {
            /* Handle break or continue */
            if (wb->loop_status == LOOP_CONTINUE)
            {
                /* Reset the loop state */
                wb->loop_status = LOOP_NORMAL;
                wb->skip = false;
                continue;
            }
            else if (wb->loop_status == LOOP_BREAK)
            {
                break;
            }
        }
    }

    /* Done */
    parser->pop_block(wb);

    return ret;
}

/* Reports an error. Always returns parse_execution_errored, so you can assign the result to an 'errored' variable */
parse_execution_result_t parse_execution_context_t::report_error(const parse_node_t &node, const wchar_t *fmt, ...)
{
    if (parser->show_errors)
    {
        /* Create an error */
        parse_error_t error;
        error.source_start = node.source_start;
        error.source_length = node.source_length;
        error.code = parse_error_syntax; //hackish

        va_list va;
        va_start(va, fmt);
        error.text = vformat_string(fmt, va);
        va_end(va);

        /* Get a backtrace */
        wcstring backtrace_and_desc;
        const parse_error_list_t error_list = parse_error_list_t(1, error);
        parser->get_backtrace(src, error_list, &backtrace_and_desc);

        fprintf(stderr, "%ls", backtrace_and_desc.c_str());
    }

    return parse_execution_errored;
}

/* Reoports an unmatched wildcard error and returns parse_execution_errored */
parse_execution_result_t parse_execution_context_t::report_unmatched_wildcard_error(const parse_node_t &unmatched_wildcard)
{
    proc_set_last_status(STATUS_UNMATCHED_WILDCARD);
    /* For reasons I cannot explain, unmatched wildcards are only reported in interactive use. */
    if (get_is_interactive())
    {
        return report_error(unmatched_wildcard, WILDCARD_ERR_MSG, get_source(unmatched_wildcard).c_str());
    }
    else
    {
        return parse_execution_errored;
    }
}

/* Handle the case of command not found */
void parse_execution_context_t::handle_command_not_found(const wcstring &cmd_str, const parse_node_t &statement_node, int err_code)
{
    assert(statement_node.type == symbol_plain_statement);

    /* We couldn't find the specified command. This is a non-fatal error. We want to set the exit status to 127, which is the standard number used by other shells like bash and zsh. */

    const wchar_t * const cmd = cmd_str.c_str();
    const wchar_t * const equals_ptr = wcschr(cmd, L'=');
    if (equals_ptr != NULL)
    {
        /* Try to figure out if this is a pure variable assignment (foo=bar), or if this appears to be running a command (foo=bar ruby...) */

        const wcstring name_str = wcstring(cmd, equals_ptr - cmd); //variable name, up to the =
        const wcstring val_str = wcstring(equals_ptr + 1); //variable value, past the =


        const parse_node_tree_t::parse_node_list_t args = tree.find_nodes(statement_node, symbol_argument, 1);

        if (! args.empty())
        {
            const wcstring argument = get_source(*args.at(0));

            wcstring ellipsis_str = wcstring(1, ellipsis_char);
            if (ellipsis_str == L"$")
                ellipsis_str = L"...";

            /* Looks like a command */
            this->report_error(statement_node,
                               _(L"Unknown command '%ls'. Did you mean to run %ls with a modified environment? Try 'env %ls=%ls %ls%ls'. See the help section on the set command by typing 'help set'."),
                               cmd,
                               argument.c_str(),
                               name_str.c_str(),
                               val_str.c_str(),
                               argument.c_str(),
                               ellipsis_str.c_str());
        }
        else
        {
            this->report_error(statement_node,
                               COMMAND_ASSIGN_ERR_MSG,
                               cmd,
                               name_str.c_str(),
                               val_str.c_str());
        }
    }
    else if (cmd[0]==L'$' || cmd[0] == VARIABLE_EXPAND || cmd[0] == VARIABLE_EXPAND_SINGLE)
    {

        const env_var_t val_wstr = env_get_string(cmd+1);
        const wchar_t *val = val_wstr.missing() ? NULL : val_wstr.c_str();
        if (val)
        {
            this->report_error(statement_node,
                               _(L"Variables may not be used as commands. Instead, define a function like 'function %ls; %ls $argv; end' or use the eval builtin instead, like 'eval %ls'. See the help section for the function command by typing 'help function'."),
                               cmd+1,
                               val,
                               cmd,
                               cmd);
        }
        else
        {
            this->report_error(statement_node,
                               _(L"Variables may not be used as commands. Instead, define a function or use the eval builtin instead, like 'eval %ls'. See the help section for the function command by typing 'help function'."),
                               cmd,
                               cmd);
        }
    }
    else if (wcschr(cmd, L'$'))
    {
        this->report_error(statement_node,
                           _(L"Commands may not contain variables. Use the eval builtin instead, like 'eval %ls'. See the help section for the eval command by typing 'help eval'."),
                           cmd,
                           cmd);
    }
    else if (err_code!=ENOENT)
    {
        this->report_error(statement_node,
                           _(L"The file '%ls' is not executable by this user"),
                           cmd?cmd:L"UNKNOWN");
    }
    else
    {
        /*
         Handle unrecognized commands with standard
         command not found handler that can make better
         error messages
         */

        wcstring_list_t event_args;
        event_args.push_back(cmd_str);
        event_fire_generic(L"fish_command_not_found", &event_args);

        /* Here we want to report an error (so it shows a backtrace), but with no text */
        this->report_error(statement_node, L"");
    }

    /* Set the last proc status appropriately */
    proc_set_last_status(err_code==ENOENT?STATUS_UNKNOWN_COMMAND:STATUS_NOT_EXECUTABLE);
}

/* Creates a 'normal' (non-block) process */
parse_execution_result_t parse_execution_context_t::populate_plain_process(job_t *job, process_t *proc, const parse_node_t &statement)
{
    assert(job != NULL);
    assert(proc != NULL);
    assert(statement.type == symbol_plain_statement);

    /* We may decide that a command should be an implicit cd */
    bool use_implicit_cd = false;

    /* Get the command. We expect to always get it here. */
    wcstring cmd;
    bool got_cmd = tree.command_for_plain_statement(statement, src, &cmd);
    assert(got_cmd);

    /* Expand it as a command. Return an error on failure. */
    bool expanded = expand_one(cmd, EXPAND_SKIP_CMDSUBST | EXPAND_SKIP_VARIABLES);
    if (! expanded)
    {
        report_error(statement, ILLEGAL_CMD_ERR_MSG, cmd.c_str());
        return parse_execution_errored;
    }

    /* Determine the process type */
    enum process_type_t process_type = process_type_for_command(statement, cmd);

    /* Check for stack overflow */
    if (process_type == INTERNAL_FUNCTION && parser->forbidden_function.size() > FISH_MAX_STACK_DEPTH)
    {
        this->report_error(statement, CALL_STACK_LIMIT_EXCEEDED_ERR_MSG);
        return parse_execution_errored;
    }

    wcstring path_to_external_command;
    if (process_type == EXTERNAL)
    {
        /* Determine the actual command. This may be an implicit cd. */
        bool has_command = path_get_path(cmd, &path_to_external_command);

        /* If there was no command, then we care about the value of errno after checking for it, to distinguish between e.g. no file vs permissions problem */
        const int no_cmd_err_code = errno;

        /* If the specified command does not exist, and is undecorated, try using an implicit cd. */
        if (! has_command && tree.decoration_for_plain_statement(statement) == parse_statement_decoration_none)
        {
            /* Implicit cd requires an empty argument and redirection list */
            const parse_node_t *args = get_child(statement, 1, symbol_arguments_or_redirections_list);
            if (args->child_count == 0)
            {
                /* Ok, no arguments or redirections; check to see if the first argument is a directory */
                wcstring implicit_cd_path;
                use_implicit_cd = path_can_be_implicit_cd(cmd, &implicit_cd_path);
            }
        }

        if (! has_command && ! use_implicit_cd)
        {
            /* No command */
            this->handle_command_not_found(cmd, statement, no_cmd_err_code);
            return parse_execution_errored;
        }
    }

    /* The argument list and set of IO redirections that we will construct for the process */
    wcstring_list_t argument_list;
    io_chain_t process_io_chain;
    if (use_implicit_cd)
    {
        /* Implicit cd is simple */
        argument_list.push_back(L"cd");
        argument_list.push_back(cmd);
        path_to_external_command.clear();

        /* If we have defined a wrapper around cd, use it, otherwise use the cd builtin */
        process_type = function_exists(L"cd") ? INTERNAL_FUNCTION : INTERNAL_BUILTIN;
    }
    else
    {
        /* Form the list of arguments. The command is the first argument. TODO: count hack, where we treat 'count --help' as different from 'count $foo' that expands to 'count --help'. fish 1.x never successfully did this, but it tried to! */
        const parse_node_t *unmatched_wildcard = NULL;
        argument_list = this->determine_arguments(statement, &unmatched_wildcard);
        argument_list.insert(argument_list.begin(), cmd);

        /* If we were not able to expand any wildcards, here is the first one that failed */
        if (unmatched_wildcard != NULL)
        {
            job_set_flag(job, JOB_WILDCARD_ERROR, 1);
            report_unmatched_wildcard_error(*unmatched_wildcard);
            return parse_execution_errored;
        }

        /* The set of IO redirections that we construct for the process */
        if (! this->determine_io_chain(statement, &process_io_chain))
        {
            return parse_execution_errored;
        }

        /* Determine the process type */
        process_type = process_type_for_command(statement, cmd);
    }


    /* Populate the process */
    proc->type = process_type;
    proc->set_argv(argument_list);
    proc->set_io_chain(process_io_chain);
    proc->actual_cmd = path_to_external_command;
    return parse_execution_success;
}

/* Determine the list of arguments, expanding stuff. If we have a wildcard and none could be expanded, return the unexpandable wildcard node by reference. */
wcstring_list_t parse_execution_context_t::determine_arguments(const parse_node_t &parent, const parse_node_t **out_unmatched_wildcard_node)
{
    wcstring_list_t argument_list;

    /* Whether we failed to match any wildcards, and succeeded in matching any wildcards */
    bool unmatched_wildcard = false, matched_wildcard = false;

    /* First node that failed to expand as a wildcard (if any) */
    const parse_node_t *unmatched_wildcard_node = NULL;

    /* Get all argument nodes underneath the statement */
    const parse_node_tree_t::parse_node_list_t argument_nodes = tree.find_nodes(parent, symbol_argument);
    argument_list.reserve(argument_nodes.size());
    for (size_t i=0; i < argument_nodes.size(); i++)
    {
        const parse_node_t &arg_node = *argument_nodes.at(i);

        /* Expect all arguments to have source */
        assert(arg_node.has_source());
        const wcstring arg_str = arg_node.get_source(src);

        /* Expand this string */
        std::vector<completion_t> arg_expanded;
        int expand_ret = expand_string(arg_str, arg_expanded, EXPAND_NO_DESCRIPTIONS);
        switch (expand_ret)
        {
            case EXPAND_ERROR:
            {
                this->report_error(arg_node,
                                   _(L"Could not expand string '%ls'"),
                                   arg_str.c_str());
                break;
            }

            case EXPAND_WILDCARD_NO_MATCH:
            {
                /* Store the node that failed to expand */
                unmatched_wildcard = true;
                if (! unmatched_wildcard_node)
                {
                    unmatched_wildcard_node = &arg_node;
                }
                break;
            }

            case EXPAND_WILDCARD_MATCH:
            {
                matched_wildcard = true;
                break;
            }

            case EXPAND_OK:
            {
                break;
            }
        }

        /* Now copy over any expanded arguments */
        for (size_t i=0; i < arg_expanded.size(); i++)
        {
            argument_list.push_back(arg_expanded.at(i).completion);
        }
    }

    /* Return if we had a wildcard problem */
    if (out_unmatched_wildcard_node != NULL && unmatched_wildcard && ! matched_wildcard)
    {
        *out_unmatched_wildcard_node = unmatched_wildcard_node;
    }

    return argument_list;
}

bool parse_execution_context_t::determine_io_chain(const parse_node_t &statement_node, io_chain_t *out_chain)
{
    io_chain_t result;
    bool errored = false;

    /* We are called with a statement of varying types. We require that the statement have an arguments_or_redirections_list child. */
    const parse_node_t &args_and_redirections_list = tree.find_child(statement_node, symbol_arguments_or_redirections_list);

    /* Get all redirection nodes underneath the statement */
    const parse_node_tree_t::parse_node_list_t redirect_nodes = tree.find_nodes(args_and_redirections_list, symbol_redirection);
    for (size_t i=0; i < redirect_nodes.size(); i++)
    {
        const parse_node_t &redirect_node = *redirect_nodes.at(i);

        int source_fd = -1; /* source fd */
        wcstring target; /* file path or target fd */
        enum token_type redirect_type = tree.type_for_redirection(redirect_node, src, &source_fd, &target);

        /* PCA: I can't justify this EXPAND_SKIP_VARIABLES flag. It was like this when I got here. */
        bool target_expanded = expand_one(target, no_exec ? EXPAND_SKIP_VARIABLES : 0);
        if (! target_expanded || target.empty())
        {
            /* Should improve this error message */
            errored = report_error(redirect_node,
                                   _(L"Invalid redirection target: %ls"),
                                   target.c_str());
        }


        /* Generate the actual IO redirection */
        shared_ptr<io_data_t> new_io;
        assert(redirect_type != TOK_NONE);
        switch (redirect_type)
        {
            case TOK_REDIRECT_FD:
            {
                if (target == L"-")
                {
                    new_io.reset(new io_close_t(source_fd));
                }
                else
                {
                    wchar_t *end = NULL;
                    errno = 0;
                    int old_fd = fish_wcstoi(target.c_str(), &end, 10);
                    if (old_fd < 0 || errno || *end)
                    {
                        errored = report_error(redirect_node,
                                               _(L"Requested redirection to '%ls', which is not a valid file descriptor"),
                                               target.c_str());
                    }
                    else
                    {
                        new_io.reset(new io_fd_t(source_fd, old_fd));
                    }
                }
                break;
            }

            case TOK_REDIRECT_OUT:
            case TOK_REDIRECT_APPEND:
            case TOK_REDIRECT_IN:
            case TOK_REDIRECT_NOCLOB:
            {
                int oflags = oflags_for_redirection_type(redirect_type);
                io_file_t *new_io_file = new io_file_t(source_fd, target, oflags);
                new_io.reset(new_io_file);
                break;
            }

            default:
            {
                // Should be unreachable
                fprintf(stderr, "Unexpected redirection type %ld. aborting.\n", (long)redirect_type);
                PARSER_DIE();
                break;
            }
        }

        /* Append the new_io if we got one */
        if (new_io.get() != NULL)
        {
            result.push_back(new_io);
        }
    }

    if (out_chain && ! errored)
    {
        std::swap(*out_chain, result);
    }
    return ! errored;
}

parse_execution_result_t parse_execution_context_t::populate_boolean_process(job_t *job, process_t *proc, const parse_node_t &bool_statement)
{
    // Handle a boolean statement
    bool skip_job = false;
    assert(bool_statement.type == symbol_boolean_statement);
    switch (bool_statement.production_idx)
    {
            // These magic numbers correspond to productions for boolean_statement
        case 0:
            // AND. Skip if the last job failed.
            skip_job = (proc_get_last_status() != 0);
            break;

        case 1:
            // OR. Skip if the last job succeeded.
            skip_job = (proc_get_last_status() == 0);
            break;

        case 2:
            // NOT. Negate it.
            job_set_flag(job, JOB_NEGATE, !job_get_flag(job, JOB_NEGATE));
            break;

        default:
        {
            fprintf(stderr, "Unexpected production in boolean statement\n");
            PARSER_DIE();
            break;
        }
    }

    if (skip_job)
    {
        return parse_execution_skipped;
    }
    else
    {
        const parse_node_t &subject = *tree.get_child(bool_statement, 1, symbol_statement);
        return this->populate_job_process(job, proc, subject);
    }
}

parse_execution_result_t parse_execution_context_t::populate_block_process(job_t *job, process_t *proc, const parse_node_t &statement_node)
{
    /* We handle block statements by creating INTERNAL_BLOCK_NODE, that will bounce back to us when it's time to execute them */
    assert(statement_node.type == symbol_block_statement || statement_node.type == symbol_if_statement || statement_node.type == symbol_switch_statement);

    /* The set of IO redirections that we construct for the process */
    io_chain_t process_io_chain;
    bool errored = ! this->determine_io_chain(statement_node, &process_io_chain);
    if (errored)
        return parse_execution_errored;

    proc->type = INTERNAL_BLOCK_NODE;
    proc->internal_block_node = this->get_offset(statement_node);
    proc->set_io_chain(process_io_chain);
    return parse_execution_success;
}


/* Returns a process_t allocated with new. It's the caller's responsibility to delete it (!) */
parse_execution_result_t parse_execution_context_t::populate_job_process(job_t *job, process_t *proc, const parse_node_t &statement_node)
{
    assert(statement_node.type == symbol_statement);
    assert(statement_node.child_count == 1);

    // Get the "specific statement" which is boolean / block / if / switch / decorated
    const parse_node_t &specific_statement = *get_child(statement_node, 0);

    parse_execution_result_t result = parse_execution_success;

    switch (specific_statement.type)
    {
        case symbol_boolean_statement:
        {
            result = this->populate_boolean_process(job, proc, specific_statement);
            break;
        }

        case symbol_block_statement:
        case symbol_if_statement:
        case symbol_switch_statement:
        {
            result = this->populate_block_process(job, proc, specific_statement);
            break;
        }

        case symbol_decorated_statement:
        {
            /* Get the plain statement. It will pull out the decoration itself */
            const parse_node_t &plain_statement = tree.find_child(specific_statement, symbol_plain_statement);
            result = this->populate_plain_process(job, proc, plain_statement);
            break;
        }

        default:
            fprintf(stderr, "'%ls' not handled by new parser yet\n", specific_statement.describe().c_str());
            PARSER_DIE();
            break;
    }

    return result;
}


parse_execution_result_t parse_execution_context_t::populate_job_from_job_node(job_t *j, const parse_node_t &job_node, const block_t *associated_block)
{
    assert(job_node.type == symbol_job);

    /* Tell the job what its command is */
    j->set_command(get_source(job_node));

    /* We are going to construct process_t structures for every statement in the job. Get the first statement. */
    const parse_node_t *statement_node = get_child(job_node, 0, symbol_statement);
    assert(statement_node != NULL);

    parse_execution_result_t result = parse_execution_success;

    /* Create processes. Each one may fail. */
    std::vector<process_t *> processes;
    processes.push_back(new process_t());
    result = this->populate_job_process(j, processes.back(), *statement_node);

    /* Construct process_ts for job continuations (pipelines), by walking the list until we hit the terminal (empty) job continuation */
    const parse_node_t *job_cont = get_child(job_node, 1, symbol_job_continuation);
    assert(job_cont != NULL);
    while (result == parse_execution_success && job_cont->child_count > 0)
    {
        assert(job_cont->type == symbol_job_continuation);

        /* Handle the pipe, whose fd may not be the obvious stdout */
        const parse_node_t &pipe_node = *get_child(*job_cont, 0, parse_token_type_pipe);
        int pipe_write_fd = fd_redirected_by_pipe(get_source(pipe_node));
        if (pipe_write_fd == -1)
        {
            result = report_error(pipe_node, ILLEGAL_FD_ERR_MSG, get_source(pipe_node).c_str());
            break;
        }
        processes.back()->pipe_write_fd = pipe_write_fd;

        /* Get the statement node and make a process from it */
        const parse_node_t *statement_node = get_child(*job_cont, 1, symbol_statement);
        assert(statement_node != NULL);

        /* Store the new process (and maybe with an error) */
        processes.push_back(new process_t());
        result = this->populate_job_process(j, processes.back(), *statement_node);

        /* Get the next continuation */
        job_cont = get_child(*job_cont, 2, symbol_job_continuation);
        assert(job_cont != NULL);
    }

    /* Return what happened */
    if (result == parse_execution_success)
    {
        /* Link up the processes */
        assert(! processes.empty());
        j->first_process = processes.at(0);
        for (size_t i=1 ; i < processes.size(); i++)
        {
            processes.at(i-1)->next = processes.at(i);
        }
    }
    else
    {
        /* Clean up processes */
        for (size_t i=0; i < processes.size(); i++)
        {
            const process_t *proc = processes.at(i);
            processes.at(i) = NULL;
            delete proc;
        }
    }
    return result;
}

parse_execution_result_t parse_execution_context_t::run_1_job(const parse_node_t &job_node, const block_t *associated_block)
{
    parse_execution_result_t result = parse_execution_success;

    bool log_it = false;
    if (log_it)
    {
        fprintf(stderr, "%s: %ls\n", __FUNCTION__, get_source(job_node).c_str());
    }


    if (should_cancel_execution(associated_block))
    {
        return parse_execution_cancelled;
    }

    // Get terminal modes
    struct termios tmodes = {};
    if (get_is_interactive())
    {
        if (tcgetattr(STDIN_FILENO, &tmodes))
        {
            // need real error handling here
            wperror(L"tcgetattr");
            return parse_execution_errored;
        }
    }

    /* Increment the eval_level for the duration of this command */
    scoped_push<int> saved_eval_level(&eval_level, eval_level + 1);

    /* When we encounter a block construct (e.g. while loop) in the general case, we create a "block process" that has a pointer to its source. This allows us to handle block-level redirections. However, if there are no redirections, then we can just jump into the block directly, which is significantly faster. */
    if (job_is_simple_block(job_node))
    {
        const parse_node_t &statement = *get_child(job_node, 0, symbol_statement);
        const parse_node_t &specific_statement = *get_child(statement, 0);
        assert(specific_statement_type_is_redirectable_block(specific_statement));
        switch (specific_statement.type)
        {
            case symbol_block_statement:
                return this->run_block_statement(specific_statement);

            case symbol_if_statement:
                return this->run_if_statement(specific_statement);

            case symbol_switch_statement:
                return this->run_switch_statement(specific_statement);

            default:
                /* Other types should be impossible due to the specific_statement_type_is_redirectable_block check */
                PARSER_DIE();
                break;
        }
    }

    /* Profiling support */
    long long start_time = 0, parse_time = 0, exec_time = 0;
    const bool do_profile = profile;
    profile_item_t *profile_item = NULL;
    if (do_profile)
    {
        profile_item = new profile_item_t();
        profile_item->skipped = 1;
        profile_items.push_back(profile_item);
        start_time = get_time();
    }

    job_t *j = new job_t(acquire_job_id(), block_io);
    j->tmodes = tmodes;
    job_set_flag(j, JOB_CONTROL,
                 (job_control_mode==JOB_CONTROL_ALL) ||
                 ((job_control_mode == JOB_CONTROL_INTERACTIVE) && (get_is_interactive())));

    job_set_flag(j, JOB_FOREGROUND, 1);

    job_set_flag(j, JOB_TERMINAL, job_get_flag(j, JOB_CONTROL) \
                 && (!is_subshell && !is_event));

    job_set_flag(j, JOB_SKIP_NOTIFICATION, is_subshell \
                 || is_block \
                 || is_event \
                 || (!get_is_interactive()));

    /* Populate the job. This may fail for reasons like command_not_found. If this fails, an error will have been printed */
    parse_execution_result_t pop_result = this->populate_job_from_job_node(j, job_node, associated_block);

    /* Clean up the job on failure or cancellation */
    bool populated_job = (pop_result == parse_execution_success);
    if (! populated_job || this->should_cancel_execution(associated_block))
    {
        delete j;
        j = NULL;
        populated_job = false;
    }


    /* Store time it took to 'parse' the command */
    if (do_profile)
    {
        parse_time = get_time();
        profile_item->cmd = j->command();
        profile_item->skipped=parser->current_block()->skip;
    }

    if (populated_job)
    {
        /* Success. Give the job to the parser - it will clean it up. */
        parser->job_add(j);
        parser->current_block()->job = j;

        /* Check to see if this contained any external commands */
        bool job_contained_external_command = false;
        for (const process_t *proc = j->first_process; proc != NULL; proc = proc->next)
        {
            if (proc->type == EXTERNAL)
            {
                job_contained_external_command = true;
                break;
            }
        }

        /* Actually execute the job */
        exec_job(*this->parser, j);

        /* Only external commands require a new fishd barrier */
        if (!job_contained_external_command)
        {
            set_proc_had_barrier(false);
        }
    }

    /* If the job was skipped, we pretend it ran anyways */
    if (result == parse_execution_skipped)
    {
        result = parse_execution_success;
    }

    if (do_profile)
    {
        exec_time = get_time();
        profile_item->level=eval_level;
        profile_item->parse = (int)(parse_time-start_time);
        profile_item->exec=(int)(exec_time-parse_time);
        profile_item->skipped = ! populated_job;
    }

    /* Clean up jobs. */
    job_reap(0);

    /* All done */
    return result;
}

parse_execution_result_t parse_execution_context_t::run_job_list(const parse_node_t &job_list_node, const block_t *associated_block)
{
    assert(job_list_node.type == symbol_job_list);

    parse_execution_result_t result = parse_execution_success;
    const parse_node_t *job_list = &job_list_node;
    while (job_list != NULL && ! should_cancel_execution(associated_block))
    {
        assert(job_list->type == symbol_job_list);

        // Try pulling out a job
        const parse_node_t *job = tree.next_node_in_node_list(*job_list, symbol_job, &job_list);

        if (job != NULL)
        {
            result = this->run_1_job(*job, associated_block);
        }
    }

    /* Returns the last job executed */
    return result;
}

parse_execution_result_t parse_execution_context_t::eval_node_at_offset(node_offset_t offset, const block_t *associated_block, const io_chain_t &io)
{
    bool log_it = false;

    /* Don't ever expect to have an empty tree if this is called */
    assert(! tree.empty());
    assert(offset < tree.size());

    /* Apply this block IO for the duration of this function */
    scoped_push<io_chain_t> block_io_push(&block_io, io);

    const parse_node_t &node = tree.at(offset);

    if (log_it)
    {
        fprintf(stderr, "eval node: %ls\n", get_source(node).c_str());
    }

    /* Currently, we only expect to execute the top level job list, or a block node. Assert that. */
    assert(node.type == symbol_job_list || specific_statement_type_is_redirectable_block(node));

    enum parse_execution_result_t status = parse_execution_success;
    switch (node.type)
    {
        case symbol_job_list:
        {
            /* We should only get a job list if it's the very first node. This is because this is the entry point for both top-level execution (the first node) and INTERNAL_BLOCK_NODE execution (which does block statements, but never job lists) */
            assert(offset == 0);
            wcstring func_name;
            const parse_node_t *infinite_recursive_node = this->infinite_recursive_statement_in_job_list(node, &func_name);
            if (infinite_recursive_node != NULL)
            {
                /* We have an infinite recursion */
                this->report_error(*infinite_recursive_node, INFINITE_FUNC_RECURSION_ERR_MSG, func_name.c_str());
                status = parse_execution_errored;
            }
            else
            {
                /* No infinite recursion */
                status = this->run_job_list(node, associated_block);
            }
            break;
        }

        case symbol_block_statement:
            status = this->run_block_statement(node);
            break;

        case symbol_if_statement:
            status = this->run_if_statement(node);
            break;

        case symbol_switch_statement:
            status = this->run_switch_statement(node);
            break;

        default:
            /* In principle, we could support other node types. However we never expect to be passed them - see above. */
            fprintf(stderr, "Unexpected node %ls found in %s\n", node.describe().c_str(), __FUNCTION__);
            PARSER_DIE();
            break;
    }

    return status;
}