Fix error propagation in parser_t::eval

It was unconditionally returning `parse_execution_success`. This was
causing certain parser errors to incorrectly return after evaluation
with `$status` equal to `0`, as reported after `eval`, `source`, or
sub-`fish` execution.

src/parse_execution.cpp

@@ -1291,7 +1291,7 @@ parse_execution_result_t parse_execution_context_t::run_1_job(tnode_t<g::job> jo
     }
 
     job_reap(false);  // clean up jobs
-    return parse_execution_success;
+    return populated_job ? parse_execution_success : parse_execution_errored;
 }
 
 parse_execution_result_t parse_execution_context_t::run_job_conjunction(

src/parser.cpp

@@ -631,17 +631,17 @@ int parser_t::eval(wcstring cmd, const io_chain_t &io, enum block_type_t block_t
         std::fwprintf(stderr, L"%ls\n", backtrace_and_desc.c_str());
         return 1;
     }
-    this->eval(ps, io, block_type);
-    return 0;
+    return this->eval(ps, io, block_type);
 }
 
-void parser_t::eval(parsed_source_ref_t ps, const io_chain_t &io, enum block_type_t block_type) {
+int parser_t::eval(parsed_source_ref_t ps, const io_chain_t &io, enum block_type_t block_type) {
     assert(block_type == TOP || block_type == SUBST);
     if (!ps->tree.empty()) {
         // Execute the first node.
         tnode_t<grammar::job_list> start{&ps->tree, &ps->tree.front()};
-        this->eval_node(ps, start, io, block_type, nullptr /* parent */);
+        return this->eval_node(ps, start, io, block_type, nullptr /* parent */);
     }
+    return 0;
 }
 
 template <typename T>

src/parser.h

@@ -225,7 +225,8 @@ class parser_t : public std::enable_shared_from_this<parser_t> {
     int eval(wcstring cmd, const io_chain_t &io, enum block_type_t block_type);
 
     /// Evaluate the parsed source ps.
-    void eval(parsed_source_ref_t ps, const io_chain_t &io, enum block_type_t block_type);
+    /// \return 0 on success, 1 on a parse error.
+    int eval(parsed_source_ref_t ps, const io_chain_t &io, enum block_type_t block_type);
 
     /// Evaluates a node.
     /// The node type must be grammar::statement or grammar::job_list.