fish-shell/parser.cpp

/** \file parser.c

The fish parser. Contains functions for parsing and evaluating code.

*/

#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <termios.h>
#include <pwd.h>
#include <dirent.h>
#include <signal.h>
#include <algorithm>

#include "fallback.h"
#include "util.h"

#include "common.h"
#include "wutil.h"
#include "proc.h"
#include "parser.h"
#include "parser_keywords.h"
#include "tokenizer.h"
#include "exec.h"
#include "wildcard.h"
#include "function.h"
#include "builtin.h"
#include "env.h"
#include "expand.h"
#include "reader.h"
#include "sanity.h"
#include "env_universal.h"
#include "event.h"
#include "intern.h"
#include "parse_util.h"
#include "path.h"
#include "signal.h"
#include "complete.h"
#include "parse_tree.h"
#include "parse_execution.h"

/**
   Error message for tokenizer error. The tokenizer message is
   appended to this message.
*/
#define TOK_ERR_MSG _( L"Tokenizer error: '%ls'")

/**
   Error for evaluating in illegal scope
*/
#define INVALID_SCOPE_ERR_MSG _( L"Tried to evaluate commands using invalid block type '%ls'" )

/**
   Error for wrong token type
*/
#define UNEXPECTED_TOKEN_ERR_MSG _( L"Unexpected token of type '%ls'")

/**
   While block description
*/
#define WHILE_BLOCK N_( L"'while' block" )

/**
   For block description
*/
#define FOR_BLOCK N_( L"'for' block" )

/**
   Breakpoint block
*/
#define BREAKPOINT_BLOCK N_( L"Block created by breakpoint" )

/**
   If block description
*/
#define IF_BLOCK N_( L"'if' conditional block" )

/**
   Function definition block description
*/
#define FUNCTION_DEF_BLOCK N_( L"function definition block" )

/**
   Function invocation block description
*/
#define FUNCTION_CALL_BLOCK N_( L"function invocation block" )

/**
   Function invocation block description
*/
#define FUNCTION_CALL_NO_SHADOW_BLOCK N_( L"function invocation block with no variable shadowing" )

/**
   Switch block description
*/
#define SWITCH_BLOCK N_( L"'switch' block" )

/**
   Fake block description
*/
#define FAKE_BLOCK N_( L"unexecutable block" )

/**
   Top block description
*/
#define TOP_BLOCK N_( L"global root block" )

/**
   Command substitution block description
*/
#define SUBST_BLOCK N_( L"command substitution block" )

/**
   Begin block description
*/
#define BEGIN_BLOCK N_( L"'begin' unconditional block" )

/**
   Source block description
*/
#define SOURCE_BLOCK N_( L"Block created by the . builtin" )

/**
   Source block description
*/
#define EVENT_BLOCK N_( L"event handler block" )

/**
   Unknown block description
*/
#define UNKNOWN_BLOCK N_( L"unknown/invalid block" )


/**
   Datastructure to describe a block type, like while blocks, command substitution blocks, etc.
*/
struct block_lookup_entry
{

    /**
       The block type id. The legal values are defined in parser.h.
    */
    block_type_t type;

    /**
       The name of the builtin that creates this type of block, if any.
    */
    const wchar_t *name;

    /**
       A description of this block type
    */
    const wchar_t *desc;
}
;

/**
   List of all legal block types
*/
static const struct block_lookup_entry block_lookup[]=
{
    { WHILE, L"while", WHILE_BLOCK },
    { FOR, L"for", FOR_BLOCK },
    { IF, L"if", IF_BLOCK },
    { FUNCTION_DEF, L"function", FUNCTION_DEF_BLOCK },
    { FUNCTION_CALL, 0, FUNCTION_CALL_BLOCK },
    { FUNCTION_CALL_NO_SHADOW, 0, FUNCTION_CALL_NO_SHADOW_BLOCK },
    { SWITCH, L"switch", SWITCH_BLOCK },
    { FAKE, 0, FAKE_BLOCK },
    { TOP, 0, TOP_BLOCK },
    { SUBST, 0, SUBST_BLOCK },
    { BEGIN, L"begin", BEGIN_BLOCK },
    { SOURCE, L".", SOURCE_BLOCK },
    { EVENT, 0, EVENT_BLOCK },
    { BREAKPOINT, L"breakpoint", BREAKPOINT_BLOCK },
    { (block_type_t)0, 0, 0 }
};

// Given a file path, return something nicer. Currently we just "unexpand" tildes.
static wcstring user_presentable_path(const wcstring &path)
{
    return replace_home_directory_with_tilde(path);
}


parser_t::parser_t(enum parser_type_t type, bool errors) :
    parser_type(type),
    show_errors(errors),
    error_code(0),
    err_pos(0),
    cancellation_requested(false),
    is_within_fish_initialization(false),
    current_tokenizer(NULL),
    current_tokenizer_pos(0)
{
}

/* A pointer to the principal parser (which is a static local) */
static parser_t *s_principal_parser = NULL;

parser_t &parser_t::principal_parser(void)
{
    ASSERT_IS_NOT_FORKED_CHILD();
    ASSERT_IS_MAIN_THREAD();
    static parser_t parser(PARSER_TYPE_GENERAL, true);
    if (! s_principal_parser)
    {
        s_principal_parser = &parser;
    }
    return parser;
}

void parser_t::set_is_within_fish_initialization(bool flag)
{
    is_within_fish_initialization = flag;
}

void parser_t::skip_all_blocks(void)
{
    /* Tell all blocks to skip */
    if (s_principal_parser)
    {
        s_principal_parser->cancellation_requested = true;

        //write(2, "Cancelling blocks\n", strlen("Cancelling blocks\n"));
        for (size_t i=0; i < s_principal_parser->block_count(); i++)
        {
            s_principal_parser->block_at_index(i)->skip = true;
        }
    }
}

void parser_t::push_block(block_t *new_current)
{
    const enum block_type_t type = new_current->type();
    new_current->src_lineno = parser_t::get_lineno();
    new_current->src_filename = parser_t::current_filename()?intern(parser_t::current_filename()):0;

    const block_t *old_current = this->current_block();
    if (old_current && old_current->skip)
    {
        new_current->skip = true;
    }

    /*
      New blocks should be skipped if the outer block is skipped,
      except TOP ans SUBST block, which open up new environments. Fake
      blocks should always be skipped. Rather complicated... :-(
    */
    new_current->skip = old_current ? old_current->skip : 0;

    /*
      Type TOP and SUBST are never skipped
    */
    if (type == TOP || type == SUBST)
    {
        new_current->skip = 0;
    }

    /*
      Fake blocks and function definition blocks are never executed
    */
    if (type == FAKE || type == FUNCTION_DEF)
    {
        new_current->skip = 1;
    }

    new_current->job = 0;
    new_current->loop_status=LOOP_NORMAL;

    this->block_stack.push_back(new_current);

    if ((new_current->type() != FUNCTION_DEF) &&
            (new_current->type() != FAKE) &&
            (new_current->type() != TOP))
    {
        env_push(type == FUNCTION_CALL);
        new_current->wants_pop_env = true;
    }
}

void parser_t::pop_block()
{
    if (block_stack.empty())
    {
        debug(1,
              L"function %s called on empty block stack.",
              __func__);
        bugreport();
        return;
    }

    block_t *old = block_stack.back();
    block_stack.pop_back();

    if (old->wants_pop_env)
        env_pop();

    delete old;
}

void parser_t::pop_block(const block_t *expected)
{
    assert(expected == this->current_block());
    this->pop_block();
}

const wchar_t *parser_t::get_block_desc(int block) const
{
    for (size_t i=0; block_lookup[i].desc; i++)
    {
        if (block_lookup[i].type == block)
        {
            return _(block_lookup[i].desc);
        }
    }
    return _(UNKNOWN_BLOCK);
}

const block_t *parser_t::block_at_index(size_t idx) const
{
    /* 0 corresponds to the last element in our vector */
    size_t count = block_stack.size();
    return idx < count ? block_stack.at(count - idx - 1) : NULL;
}

block_t *parser_t::block_at_index(size_t idx)
{
    size_t count = block_stack.size();
    return idx < count ? block_stack.at(count - idx - 1) : NULL;
}

const block_t *parser_t::current_block() const
{
    return block_stack.empty() ? NULL : block_stack.back();
}

block_t *parser_t::current_block()
{
    return block_stack.empty() ? NULL : block_stack.back();
}

void parser_t::forbid_function(const wcstring &function)
{
    forbidden_function.push_back(function);
}

void parser_t::allow_function()
{
    /*
      if( al_peek( &forbidden_function) )
      debug( 2, L"Allow %ls\n", al_peek( &forbidden_function)  );
    */
    forbidden_function.pop_back();
}

void parser_t::error(int ec, size_t p, const wchar_t *str, ...)
{
    va_list va;

    CHECK(str,);

    error_code = ec;

    // note : p may be -1
    err_pos = static_cast<int>(p);

    va_start(va, str);
    err_buff = vformat_string(str, va);
    va_end(va);
}

/**
   Print profiling information to the specified stream
*/
static void print_profile(const std::vector<profile_item_t*> &items,
                          FILE *out)
{
    for (size_t pos = 0; pos < items.size(); pos++)
    {
        const profile_item_t *me, *prev;
        size_t i;
        int my_time;

        me = items.at(pos);
        if (!me->skipped)
        {
            my_time=me->parse+me->exec;

            for (i=pos+1; i<items.size(); i++)
            {
                prev = items.at(i);
                if (prev->skipped)
                {
                    continue;
                }

                if (prev->level <= me->level)
                {
                    break;
                }

                if (prev->level > me->level+1)
                {
                    continue;
                }

                my_time -= prev->parse;
                my_time -= prev->exec;
            }

            if (me->cmd.size() > 0)
            {
                if (fwprintf(out, L"%d\t%d\t", my_time, me->parse+me->exec) < 0)
                {
                    wperror(L"fwprintf");
                    return;
                }

                for (i=0; i<me->level; i++)
                {
                    if (fwprintf(out, L"-") < 0)
                    {
                        wperror(L"fwprintf");
                        return;
                    }

                }
                if (fwprintf(out, L"> %ls\n", me->cmd.c_str()) < 0)
                {
                    wperror(L"fwprintf");
                    return;
                }

            }
        }
    }
}

void parser_t::emit_profiling(const char *path) const
{
    /* Save profiling information. OK to not use CLO_EXEC here because this is called while fish is dying (and hence will not fork) */
    FILE *f = fopen(path, "w");
    if (!f)
    {
        debug(1,
              _(L"Could not write profiling information to file '%s'"),
              path);
    }
    else
    {
        if (fwprintf(f,
                     _(L"Time\tSum\tCommand\n"),
                     profile_items.size()) < 0)
        {
            wperror(L"fwprintf");
        }
        else
        {
            print_profile(profile_items, f);
        }

        if (fclose(f))
        {
            wperror(L"fclose");
        }
    }
}

/**
   Print error message to string if an error has occured while parsing

   \param target the buffer to write to
   \param prefix: The string token to prefix the each line with. Usually the name of the command trying to parse something.
*/
void parser_t::print_errors(wcstring &target, const wchar_t *prefix)
{
    CHECK(prefix,);

    if (error_code && ! err_buff.empty())
    {
        int tmp;

        append_format(target, L"%ls: %ls\n", prefix, err_buff.c_str());

        tmp = current_tokenizer_pos;
        current_tokenizer_pos = err_pos;

        target.append(this->current_line());

        current_tokenizer_pos=tmp;
    }
}

/**
   Print error message to stderr if an error has occured while parsing
*/
void parser_t::print_errors_stderr()
{
    if (error_code && ! err_buff.empty())
    {
        debug(0, L"%ls", err_buff.c_str());
        int tmp;

        tmp = current_tokenizer_pos;
        current_tokenizer_pos = err_pos;

        wcstring current_line = this->current_line();
        fwprintf(stderr, L"%ls", current_line.c_str());

        current_tokenizer_pos=tmp;
    }
}

void parser_t::eval_args(const wchar_t *line, std::vector<completion_t> &args)
{
    expand_flags_t eflags = 0;
    if (! show_errors)
        eflags |= EXPAND_NO_DESCRIPTIONS;
    if (this->parser_type != PARSER_TYPE_GENERAL)
        eflags |= EXPAND_SKIP_CMDSUBST;

    bool do_loop=1;

    if (! line) return;

    // PCA we need to suppress calling proc_push_interactive off of the main thread.
    if (this->parser_type == PARSER_TYPE_GENERAL)
        proc_push_interactive(0);

    tokenizer_t tok(line, (show_errors ? 0 : TOK_SQUASH_ERRORS));

    /*
      eval_args may be called while evaulating another command, so we
      save the previous tokenizer and restore it on exit
    */
    scoped_push<tokenizer_t*> tokenizer_push(&current_tokenizer, &tok);
    scoped_push<int> tokenizer_pos_push(&current_tokenizer_pos, 0);

    error_code=0;

    for (; do_loop && tok_has_next(&tok) ; tok_next(&tok))
    {
        current_tokenizer_pos = tok_get_pos(&tok);
        switch (tok_last_type(&tok))
        {
            case TOK_STRING:
            {
                const wcstring tmp = tok_last(&tok);
                if (expand_string(tmp, args, eflags) == EXPAND_ERROR)
                {
                    err_pos=tok_get_pos(&tok);
                    do_loop=0;
                }
                break;
            }

            case TOK_END:
            {
                break;
            }

            case TOK_ERROR:
            {
                if (show_errors)
                    error(SYNTAX_ERROR,
                          tok_get_pos(&tok),
                          TOK_ERR_MSG,
                          tok_last(&tok));

                do_loop=0;
                break;
            }

            default:
            {
                if (show_errors)
                    error(SYNTAX_ERROR,
                          tok_get_pos(&tok),
                          UNEXPECTED_TOKEN_ERR_MSG,
                          tok_get_desc(tok_last_type(&tok)));

                do_loop=0;
                break;
            }
        }
    }

    if (show_errors)
        this->print_errors_stderr();

    if (this->parser_type == PARSER_TYPE_GENERAL)
        proc_pop_interactive();
}

void parser_t::stack_trace(size_t block_idx, wcstring &buff) const
{
    /*
      Check if we should end the recursion
    */
    if (block_idx >= this->block_count())
        return;

    const block_t *b = this->block_at_index(block_idx);

    if (b->type()==EVENT)
    {
        /*
          This is an event handler
        */
        const event_block_t *eb = static_cast<const event_block_t *>(b);
        wcstring description = event_get_desc(eb->event);
        append_format(buff, _(L"in event handler: %ls\n"), description.c_str());
        buff.append(L"\n");

        /*
          Stop recursing at event handler. No reason to believe that
          any other code is relevant.

          It might make sense in the future to continue printing the
          stack trace of the code that invoked the event, if this is a
          programmatic event, but we can't currently detect that.
        */
        return;
    }

    if (b->type() == FUNCTION_CALL || b->type() == FUNCTION_CALL_NO_SHADOW || b->type()==SOURCE || b->type()==SUBST)
    {
        /*
          These types of blocks should be printed
        */

        int i;

        switch (b->type())
        {
            case SOURCE:
            {
                const source_block_t *sb = static_cast<const source_block_t*>(b);
                const wchar_t *source_dest = sb->source_file;
                append_format(buff, _(L"from sourcing file %ls\n"), user_presentable_path(source_dest).c_str());
                break;
            }
            case FUNCTION_CALL:
            case FUNCTION_CALL_NO_SHADOW:
            {
                const function_block_t *fb = static_cast<const function_block_t*>(b);
                append_format(buff, _(L"in function '%ls'\n"), fb->name.c_str());
                break;
            }
            case SUBST:
            {
                append_format(buff, _(L"in command substitution\n"));
                break;
            }

            default: /* Can't get here */
                break;
        }

        const wchar_t *file = b->src_filename;

        if (file)
        {
            append_format(buff,
                          _(L"\tcalled on line %d of file %ls\n"),
                          b->src_lineno,
                          user_presentable_path(file).c_str());
        }
        else if (is_within_fish_initialization)
        {
            append_format(buff, _(L"\tcalled during startup\n"));
        }
        else
        {
            append_format(buff, _(L"\tcalled on standard input\n"));
        }

        if (b->type() == FUNCTION_CALL)
        {
            const function_block_t *fb = static_cast<const function_block_t *>(b);
            const process_t * const process = fb->process;
            if (process->argv(1))
            {
                wcstring tmp;

                for (i=1; process->argv(i); i++)
                {
                    if (i > 1)
                        tmp.push_back(L' ');
                    tmp.append(process->argv(i));
                }
                append_format(buff, _(L"\twith parameter list '%ls'\n"), tmp.c_str());
            }
        }

        append_format(buff, L"\n");
    }

    /*
      Recursively print the next block
    */
    parser_t::stack_trace(block_idx + 1, buff);
}

/**
   Returns the name of the currently evaluated function if we are
   currently evaluating a function, null otherwise. This is tested by
   moving down the block-scope-stack, checking every block if it is of
   type FUNCTION_CALL.
*/
const wchar_t *parser_t::is_function() const
{
    // PCA: Have to make this a string somehow
    ASSERT_IS_MAIN_THREAD();

    const wchar_t *result = NULL;
    for (size_t block_idx = 0; block_idx < this->block_count(); block_idx++)
    {
        const block_t *b = this->block_at_index(block_idx);
        if (b->type() == FUNCTION_CALL || b->type() == FUNCTION_CALL_NO_SHADOW)
        {
            const function_block_t *fb = static_cast<const function_block_t *>(b);
            result = fb->name.c_str();
            break;
        }
    }
    return result;
}


int parser_t::get_lineno() const
{
    int lineno = -1;
    if (! execution_contexts.empty())
    {
        lineno = execution_contexts.back()->get_current_line_number();
    }
    return lineno;
}

int parser_t::line_number_of_character_at_offset(size_t idx) const
{
    if (! current_tokenizer)
        return -1;

    int result = current_tokenizer->line_number_of_character_at_offset(idx);
    //assert(result == parse_util_lineno(tok_string( current_tokenizer ), idx));
    return result;
}

const wchar_t *parser_t::current_filename() const
{
    ASSERT_IS_MAIN_THREAD();

    for (size_t i=0; i < this->block_count(); i++)
    {
        const block_t *b = this->block_at_index(i);
        /* Note that we deliberately skip FUNCTION_CALL_NO_SHADOW here, because the only such functions in wide use are '.' and eval, and we don't want to report those */
        if (b->type() == FUNCTION_CALL)
        {
            const function_block_t *fb = static_cast<const function_block_t *>(b);
            return function_get_definition_file(fb->name);
        }
    }

    /* We query a global array for the current file name, but only do that if we are the principal parser */
    if (this == &principal_parser())
    {
        return reader_current_filename();
    }
    return NULL;
}

/**
   Calculates the on-screen width of the specified substring of the
   specified string. This function takes into account the width and
   alignment of the tab character, but other wise behaves like
   repeatedly calling wcwidth.
*/
static int printed_width(const wchar_t *str, int len)
{
    int res=0;
    int i;

    CHECK(str, 0);

    for (i=0; str[i] && i<len; i++)
    {
        if (str[i] == L'\t')
        {
            res=(res+8)&~7;
        }
        else
        {
            res += fish_wcwidth(str[i]);
        }
    }
    return res;
}


wcstring parser_t::current_line()
{
    wcstring lineinfo;

    int lineno=1;

    const wchar_t *file;
    const wchar_t *whole_str;
    const wchar_t *line;
    const wchar_t *line_end;
    int i;
    int offset;
    int current_line_width;
    const wchar_t *function_name=0;
    int current_line_start=0;

    if (!current_tokenizer)
    {
        return L"";
    }

    file = parser_t::current_filename();
    whole_str = tok_string(current_tokenizer);
    line = whole_str;

    if (!line)
        return L"";


    /*
      Calculate line number, line offset, etc.
    */
    for (i=0; i<current_tokenizer_pos && whole_str[i]; i++)
    {
        if (whole_str[i] == L'\n')
        {
            lineno++;
            current_line_start=i+1;
            line = &whole_str[i+1];
        }
    }

//  lineno = current_tokenizer_pos;


    current_line_width=printed_width(whole_str+current_line_start,
                                     current_tokenizer_pos-current_line_start);

    if ((function_name = is_function()))
    {
        lineno += function_get_definition_offset(function_name);
    }

    /*
      Copy current line from whole string
    */
    line_end = wcschr(line, L'\n');
    if (!line_end)
        line_end = line+wcslen(line);

    line = wcsndup(line, line_end-line);

    /**
       If we are not going to print a stack trace, at least print the line number and filename
    */
    if (!get_is_interactive() || is_function())
    {
        int prev_width = my_wcswidth(lineinfo.c_str());
        if (file)
        {
            append_format(lineinfo, _(L"%ls (line %d): "), file, lineno);
        }
        else if (is_within_fish_initialization)
        {
            append_format(lineinfo, L"%ls: ", _(L"Startup"), lineno);
        }
        else
        {
            append_format(lineinfo, L"%ls: ", _(L"Standard input"), lineno);
        }
        offset = my_wcswidth(lineinfo.c_str()) - prev_width;
    }
    else
    {
        offset=0;
    }

//  debug( 1, L"Current pos %d, line pos %d, file_length %d, is_interactive %d, offset %d\n", current_tokenizer_pos,  current_line_pos, wcslen(whole_str), is_interactive, offset);
    /*
      Skip printing character position if we are in interactive mode
      and the error was on the first character of the line.
    */
    if (!get_is_interactive() || is_function() || (current_line_width!=0))
    {
        // Workaround since it seems impossible to print 0 copies of a character using %*lc
        if (offset+current_line_width)
        {
            append_format(lineinfo,
                          L"%ls\n%*lc^\n",
                          line,
                          offset+current_line_width,
                          L' ');
        }
        else
        {
            append_format(lineinfo,
                          L"%ls\n^\n",
                          line);
        }
    }

    free((void *)line);
    parser_t::stack_trace(0, lineinfo);

    return lineinfo;
}


const wchar_t *parser_t::get_buffer() const
{
    return tok_string(current_tokenizer);
}


int parser_t::is_help(const wchar_t *s, int min_match)
{
    CHECK(s, 0);

    size_t len = wcslen(s);

    min_match = maxi(min_match, 3);

    return (wcscmp(L"-h", s) == 0) ||
           (len >= (size_t)min_match && (wcsncmp(L"--help", s, len) == 0));
}

void parser_t::job_add(job_t *job)
{
    assert(job != NULL);
    assert(job->first_process != NULL);
    this->my_job_list.push_front(job);
}

job_t *parser_t::job_create(const io_chain_t &io)
{
    job_t *res = new job_t(acquire_job_id(), io);
    this->my_job_list.push_front(res);

    job_set_flag(res,
                 JOB_CONTROL,
                 (job_control_mode==JOB_CONTROL_ALL) ||
                 ((job_control_mode == JOB_CONTROL_INTERACTIVE) && (get_is_interactive())));
    return res;
}

bool parser_t::job_remove(job_t *j)
{
    job_list_t::iterator iter = std::find(my_job_list.begin(), my_job_list.end(), j);
    if (iter != my_job_list.end())
    {
        my_job_list.erase(iter);
        return true;
    }
    else
    {
        debug(1, _(L"Job inconsistency"));
        sanity_lose();
        return false;
    }
}

void parser_t::job_promote(job_t *job)
{
    signal_block();

    job_list_t::iterator loc = std::find(my_job_list.begin(), my_job_list.end(), job);
    assert(loc != my_job_list.end());

    /* Move the job to the beginning */
    my_job_list.splice(my_job_list.begin(), my_job_list, loc);
    signal_unblock();
}

job_t *parser_t::job_get(job_id_t id)
{
    job_iterator_t jobs(my_job_list);
    job_t *job;
    while ((job = jobs.next()))
    {
        if (id <= 0 || job->job_id == id)
            return job;
    }
    return NULL;
}

job_t *parser_t::job_get_from_pid(int pid)
{
    job_iterator_t jobs;
    job_t *job;
    while ((job = jobs.next()))
    {
        if (job->pgid == pid)
            return job;
    }
    return 0;
}

profile_item_t *parser_t::create_profile_item()
{
    profile_item_t *result = NULL;
    if (g_profiling_active)
    {
        result = new profile_item_t();
        profile_items.push_back(result);
    }
    return result;
}


int parser_t::eval_new_parser(const wcstring &cmd, const io_chain_t &io, enum block_type_t block_type)
{
    CHECK_BLOCK(1);

    if (block_type != TOP && block_type != SUBST)
    {
        debug(1, INVALID_SCOPE_ERR_MSG, parser_t::get_block_desc(block_type));
        bugreport();
        return 1;
    }

    /* Parse the source into a tree, if we can */
    parse_node_tree_t tree;
    if (! parse_tree_from_string(cmd, parse_flag_none, &tree, NULL))
    {
        return 1;
    }


    /* Determine the initial eval level. If this is the first context, it's -1; otherwise it's the eval level of the top context. This is sort of wonky because we're stitching together a global notion of eval level from these separate objects. A better approach would be some profile object that all contexts share, and that tracks the eval levels on its own. */
    int exec_eval_level = (execution_contexts.empty() ? -1 : execution_contexts.back()->current_eval_level());

    /* Append to the execution context stack */
    parse_execution_context_t *ctx = new parse_execution_context_t(tree, cmd, this, exec_eval_level);
    execution_contexts.push_back(ctx);

    /* Execute the first node */
    int result = 1;
    if (! tree.empty())
    {
        result = this->eval_block_node(0, io, block_type);
    }

    /* Clean up the execution context stack */
    assert(! execution_contexts.empty() && execution_contexts.back() == ctx);
    execution_contexts.pop_back();
    delete ctx;

    return 0;
}

int parser_t::eval_block_node(node_offset_t node_idx, const io_chain_t &io, enum block_type_t block_type)
{
    /* Paranoia. It's a little frightening that we're given only a node_idx and we interpret this in the topmost execution context's tree. What happens if two trees were to be interleaved? Fortunately that cannot happen (yet); in the future we probably want some sort of reference counted trees.
    */
    parse_execution_context_t *ctx = execution_contexts.back();
    assert(ctx != NULL);

    CHECK_BLOCK(1);

    /* Handle cancellation requests. If our block stack is currently empty, then we already did successfully cancel (or there was nothing to cancel); clear the flag. If our block stack is not empty, we are still in the process of cancelling; refuse to evaluate anything */
    if (this->cancellation_requested)
    {
        if (! block_stack.empty())
        {
            return 1;
        }
        else
        {
            this->cancellation_requested = false;
        }
    }

    /* Only certain blocks are allowed */
    if ((block_type != TOP) &&
            (block_type != SUBST))
    {
        debug(1,
              INVALID_SCOPE_ERR_MSG,
              parser_t::get_block_desc(block_type));
        bugreport();
        return 1;
    }

    /* Not sure why we reap jobs here */
    job_reap(0);

    /* Start it up */
    const block_t * const start_current_block = current_block();
    block_t *scope_block = new scope_block_t(block_type);
    this->push_block(scope_block);
    int result = ctx->eval_node_at_offset(node_idx, scope_block, io);

    /* Clean up the block stack */
    this->pop_block();
    while (start_current_block != current_block())
    {
        if (current_block() == NULL)
        {
            debug(0,
                  _(L"End of block mismatch. Program terminating."));
            bugreport();
            FATAL_EXIT();
            break;
        }
        this->pop_block();
    }

    /* Reap again */
    job_reap(0);

    return result;

}

int parser_t::eval(const wcstring &cmd_str, const io_chain_t &io, enum block_type_t block_type)
{
    return this->eval_new_parser(cmd_str, io, block_type);
}


/**
   \return the block type created by the specified builtin, or -1 on error.
*/
block_type_t parser_get_block_type(const wcstring &cmd)
{
    for (size_t i=0; block_lookup[i].desc; i++)
    {
        if (block_lookup[i].name && cmd == block_lookup[i].name)
        {
            return block_lookup[i].type;
        }
    }
    return (block_type_t)-1;
}

/**
   \return the block command that createa the specified block type, or null on error.
*/
const wchar_t *parser_get_block_command(int type)
{
    for (size_t i=0; block_lookup[i].desc; i++)
    {
        if (block_lookup[i].type == type)
        {
            return block_lookup[i].name;
        }
    }
    return NULL;
}

/**
   Test if this argument contains any errors. Detected errors include
   syntax errors in command substitutions, improperly escaped
   characters and improper use of the variable expansion operator.
*/
int parser_t::parser_test_argument(const wchar_t *arg, wcstring *out, const wchar_t *prefix, int offset)
{
    int err=0;

    wchar_t *paran_begin, *paran_end;
    wchar_t *arg_cpy;
    int do_loop = 1;

    CHECK(arg, 1);

    arg_cpy = wcsdup(arg);

    while (do_loop)
    {
        switch (parse_util_locate_cmdsubst(arg_cpy,
                                           &paran_begin,
                                           &paran_end,
                                           false))
        {
            case -1:
                err=1;
                if (out)
                {
                    error(SYNTAX_ERROR,
                          offset,
                          L"Mismatched parenthesis");
                    this->print_errors(*out, prefix);
                }
                free(arg_cpy);
                return err;

            case 0:
                do_loop = 0;
                break;

            case 1:
            {

                const wcstring subst(paran_begin + 1, paran_end);
                wcstring tmp;

                tmp.append(arg_cpy, paran_begin - arg_cpy);
                tmp.push_back(INTERNAL_SEPARATOR);
                tmp.append(paran_end+1);

//        debug( 1, L"%ls -> %ls %ls", arg_cpy, subst, tmp.buff );

                parse_error_list_t errors;
                err |= parse_util_detect_errors(subst, &errors);
                if (out && ! errors.empty())
                {
                    out->append(parse_errors_description(errors, subst, prefix));
                }

                free(arg_cpy);
                arg_cpy = wcsdup(tmp.c_str());

                break;
            }
        }
    }

    wcstring unesc;
    if (! unescape_string(arg_cpy, &unesc, UNESCAPE_SPECIAL))
    {
        if (out)
        {
            error(SYNTAX_ERROR,
                  offset,
                  L"Invalid token '%ls'", arg_cpy);
            print_errors(*out, prefix);
        }
        return 1;
    }
    else
    {
        /* Check for invalid variable expansions */
        const size_t unesc_size = unesc.size();
        for (size_t idx = 0; idx < unesc_size; idx++)
        {
            switch (unesc.at(idx))
            {
                case VARIABLE_EXPAND:
                case VARIABLE_EXPAND_SINGLE:
                {
                    wchar_t next_char = (idx + 1 < unesc_size ? unesc.at(idx + 1) : L'\0');

                    if (next_char != VARIABLE_EXPAND &&
                            next_char != VARIABLE_EXPAND_SINGLE &&
                            ! wcsvarchr(next_char))
                    {
                        err=1;
                        if (out)
                        {
                            expand_variable_error(*this, unesc, idx, offset);
                            print_errors(*out, prefix);
                        }
                    }

                    break;
                }
            }
        }
    }

    free(arg_cpy);

    return err;

}

int parser_t::test_args(const  wchar_t * buff, wcstring *out, const wchar_t *prefix)
{
    int do_loop = 1;
    int err = 0;

    CHECK(buff, 1);

    tokenizer_t tok(buff, 0);
    scoped_push<tokenizer_t*> tokenizer_push(&current_tokenizer, &tok);
    scoped_push<int> tokenizer_pos_push(&current_tokenizer_pos);

    for (; do_loop && tok_has_next(&tok); tok_next(&tok))
    {
        current_tokenizer_pos = tok_get_pos(&tok);
        switch (tok_last_type(&tok))
        {

            case TOK_STRING:
            {
                err |= parser_test_argument(tok_last(&tok), out, prefix, tok_get_pos(&tok));
                break;
            }

            case TOK_END:
            {
                break;
            }

            case TOK_ERROR:
            {
                if (out)
                {
                    error(SYNTAX_ERROR,
                          tok_get_pos(&tok),
                          TOK_ERR_MSG,
                          tok_last(&tok));
                    print_errors(*out, prefix);
                }
                err=1;
                do_loop=0;
                break;
            }

            default:
            {
                if (out)
                {
                    error(SYNTAX_ERROR,
                          tok_get_pos(&tok),
                          UNEXPECTED_TOKEN_ERR_MSG,
                          tok_get_desc(tok_last_type(&tok)));
                    print_errors(*out, prefix);
                }
                err=1;
                do_loop=0;
                break;
            }
        }
    }

    error_code=0;

    return err;
}

// helper type used in parser::test below
struct block_info_t
{
    int position; //tokenizer position
    block_type_t type; //type of the block
};

void parser_t::get_backtrace(const wcstring &src, const parse_error_list_t &errors, wcstring *output) const
{
    assert(output != NULL);
    if (! errors.empty())
    {
        const parse_error_t &err = errors.at(0);

        // Determine which line we're on
        assert(err.source_start <= src.size());
        size_t which_line = 1 + std::count(src.begin(), src.begin() + err.source_start, L'\n');

        // Don't include the caret if we're interactive, this is the first line of text, and our source is at its beginning, because then it's obvious
        bool skip_caret = (get_is_interactive() && which_line == 1 && err.source_start == 0);
        
        wcstring prefix;
        
        const wchar_t *filename = this->current_filename();
        if (filename)
        {
            prefix = format_string(_(L"%ls (line %lu): "), user_presentable_path(filename).c_str(), which_line);
        }
        else
        {
            prefix = L"fish: ";
        }

        const wcstring description = err.describe_with_prefix(src, prefix, skip_caret);
        if (! description.empty())
        {
            output->append(description);
            output->push_back(L'\n');
        }
        this->stack_trace(0, *output);
    }
}

block_t::block_t(block_type_t t) :
    block_type(t),
    skip(),
    had_command(),
    tok_pos(),
    node_offset(NODE_OFFSET_INVALID),
    loop_status(),
    job(),
    src_filename(),
    src_lineno(),
    wants_pop_env(false),
    event_blocks()
{
}

block_t::~block_t()
{
}

/* Various block constructors */

if_block_t::if_block_t() : block_t(IF)
{
}

event_block_t::event_block_t(const event_t &evt) :
    block_t(EVENT),
    event(evt)
{
}

function_block_t::function_block_t(const process_t *p, const wcstring &n, bool shadows) :
    block_t(shadows ? FUNCTION_CALL : FUNCTION_CALL_NO_SHADOW),
    process(p),
    name(n)
{
}

source_block_t::source_block_t(const wchar_t *src) :
    block_t(SOURCE),
    source_file(src)
{
}

for_block_t::for_block_t() : block_t(FOR)
{
}

while_block_t::while_block_t() : block_t(WHILE)
{
}

switch_block_t::switch_block_t() : block_t(SWITCH)
{
}

fake_block_t::fake_block_t() : block_t(FAKE)
{
}

scope_block_t::scope_block_t(block_type_t type) : block_t(type)
{
    assert(type == BEGIN || type == TOP || type == SUBST);
}

breakpoint_block_t::breakpoint_block_t() : block_t(BREAKPOINT)
{
}

bool parser_use_ast(void)
{
    env_var_t var = env_get_string(L"fish_new_parser");
    if (var.missing_or_empty())
    {
        return 1;
    }
    else
    {
        return from_string<bool>(var);
    }
}