parser: try to avoid some strings being copied

src/parse_execution.cpp

@@ -734,8 +734,6 @@ parse_execution_result_t parse_execution_context_t::expand_command(
 
     // Get the unexpanded command string. We expect to always get it here.
     wcstring unexp_cmd = *command_for_plain_statement(statement, pstree->src);
-    wcstring cmd;
-    wcstring_list_t args;
 
     // Expand the string to produce completions, and report errors.
     expand_error_t expand_err =
@@ -879,7 +877,7 @@ parse_execution_result_t parse_execution_context_t::populate_plain_process(
     proc->type = process_type;
     proc->set_argv(cmd_args);
     proc->set_io_chain(process_io_chain);
-    proc->actual_cmd = path_to_external_command;
+    proc->actual_cmd = std::move(path_to_external_command);
     return parse_execution_success;
 }
 

src/parse_tree.cpp

@@ -1135,7 +1135,7 @@ const parse_node_t *parse_node_tree_t::get_child(const parse_node_t &parent, nod
     return result;
 }
 
-parsed_source_ref_t parse_source(wcstring src, parse_tree_flags_t flags, parse_error_list_t *errors,
+parsed_source_ref_t parse_source(const wcstring &src, parse_tree_flags_t flags, parse_error_list_t *errors,
                                  parse_token_type_t goal) {
     parse_node_tree_t tree;
     if (!parse_tree_from_string(src, flags, &tree, errors, goal)) return {};

src/parse_tree.h

@@ -233,7 +233,7 @@ struct parsed_source_t {
 };
 /// Return a shared pointer to parsed_source_t, or null on failure.
 using parsed_source_ref_t = std::shared_ptr<const parsed_source_t>;
-parsed_source_ref_t parse_source(wcstring src, parse_tree_flags_t flags, parse_error_list_t *errors,
+parsed_source_ref_t parse_source(const wcstring &src, parse_tree_flags_t flags, parse_error_list_t *errors,
                                  parse_token_type_t goal = symbol_job_list);
 
 #endif

src/parser.cpp

@@ -629,7 +629,7 @@ profile_item_t *parser_t::create_profile_item() {
     return result;
 }
 
-int parser_t::eval(wcstring cmd, const io_chain_t &io, enum block_type_t block_type) {
+int parser_t::eval(const wcstring &cmd, const io_chain_t &io, enum block_type_t block_type) {
     // Parse the source into a tree, if we can.
     parse_error_list_t error_list;
     parsed_source_ref_t ps = parse_source(cmd, parse_flag_none, &error_list);

src/parser.h

@@ -222,7 +222,7 @@ class parser_t : public std::enable_shared_from_this<parser_t> {
     /// \param block_type The type of block to push on the block stack
     ///
     /// \return 0 on success, 1 on a parse error.
-    int eval(wcstring cmd, const io_chain_t &io, enum block_type_t block_type);
+    int eval(const 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);