From 0bda853dc73c937d0731180df747d3721da48b79 Mon Sep 17 00:00:00 2001
From: Mahmoud Al-Qudsi <mqudsi@neosmart.net>
Date: Thu, 28 Mar 2019 19:55:23 -0500
Subject: [PATCH] Add detection of `eval` to the parser

While `eval` is still a function, this paves the way for changing that
in the future, and lets the proc/exec functions detect when an eval is
used to allow/disallow certain behaviors and optimizations.
---
 src/complete.cpp          | 8 ++++++++
 src/exec.cpp              | 1 +
 src/parse_constants.h     | 9 ++++++---
 src/parse_grammar.h       | 2 ++
 src/parse_productions.cpp | 4 ++++
 src/proc.h                | 2 ++
 6 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/complete.cpp b/src/complete.cpp
index d4091855d..c892f4482 100644
--- a/src/complete.cpp
+++ b/src/complete.cpp
@@ -1465,6 +1465,14 @@ void completer_t::perform() {
                 use_abbr = false;
                 break;
             }
+            case parse_statement_decoration_eval: {
+                use_command = true;
+                use_function = true;
+                use_builtin = true;
+                use_implicit_cd = false;
+                use_abbr = false;
+                break;
+            }
         }
 
         if (cmd_node.location_in_or_at_end_of_source_range(pos)) {
diff --git a/src/exec.cpp b/src/exec.cpp
index be1eec6b6..a6441798e 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -944,6 +944,7 @@ static bool exec_process_in_job(parser_t &parser, process_t *p, std::shared_ptr<
     // Execute the process.
     p->check_generations_before_launch();
     switch (p->type) {
+        case process_type_t::eval: /* so long as `eval` is a function */
         case process_type_t::function:
         case process_type_t::block_node: {
             // Allow buffering unless this is a deferred run. If deferred, then processes after us
diff --git a/src/parse_constants.h b/src/parse_constants.h
index 53eda65c4..2f86f05fd 100644
--- a/src/parse_constants.h
+++ b/src/parse_constants.h
@@ -97,7 +97,6 @@ const enum_map<parse_token_type_t> token_enum_map[] = {
 //
 // IMPORTANT: These enums must start at zero.
 enum parse_keyword_t {
-    parse_keyword_none = 0,
     parse_keyword_and,
     parse_keyword_begin,
     parse_keyword_builtin,
@@ -105,13 +104,15 @@ enum parse_keyword_t {
     parse_keyword_command,
     parse_keyword_else,
     parse_keyword_end,
+    parse_keyword_eval,
+    parse_keyword_exclam,
     parse_keyword_exec,
     parse_keyword_for,
     parse_keyword_function,
     parse_keyword_if,
     parse_keyword_in,
+    parse_keyword_none,
     parse_keyword_not,
-    parse_keyword_exclam,
     parse_keyword_or,
     parse_keyword_switch,
     parse_keyword_while,
@@ -125,6 +126,7 @@ const enum_map<parse_keyword_t> keyword_enum_map[] = {{parse_keyword_exclam, L"!
                                                       {parse_keyword_command, L"command"},
                                                       {parse_keyword_else, L"else"},
                                                       {parse_keyword_end, L"end"},
+                                                      {parse_keyword_eval, L"eval"},
                                                       {parse_keyword_exec, L"exec"},
                                                       {parse_keyword_for, L"for"},
                                                       {parse_keyword_function, L"function"},
@@ -144,7 +146,8 @@ enum parse_statement_decoration_t {
     parse_statement_decoration_none,
     parse_statement_decoration_command,
     parse_statement_decoration_builtin,
-    parse_statement_decoration_exec
+    parse_statement_decoration_exec,
+    parse_statement_decoration_eval,
 };
 
 // Boolean statement types, stored in node tag.
diff --git a/src/parse_grammar.h b/src/parse_grammar.h
index b6b1cb2ee..03e163ae1 100644
--- a/src/parse_grammar.h
+++ b/src/parse_grammar.h
@@ -334,6 +334,8 @@ DEF_ALT(decorated_statement) {
     using cmds = seq<keyword<parse_keyword_command>, plain_statement>;
     using builtins = seq<keyword<parse_keyword_builtin>, plain_statement>;
     using execs = seq<keyword<parse_keyword_exec>, plain_statement>;
+    // using evals = seq<keyword<parse_keyword_eval>, plain_statement>;
+    using evals = single<plain_statement>; /* so long as `eval` is a function */
     ALT_BODY(decorated_statement, plains, cmds, builtins, execs);
 };
 
diff --git a/src/parse_productions.cpp b/src/parse_productions.cpp
index 4718d826a..2e60f3b46 100644
--- a/src/parse_productions.cpp
+++ b/src/parse_productions.cpp
@@ -314,6 +314,10 @@ RESOLVE(decorated_statement) {
             *out_tag = parse_statement_decoration_exec;
             return production_for<execs>();
         }
+        case parse_keyword_eval: {
+            *out_tag = parse_statement_decoration_eval;
+            return production_for<evals>();
+        }
         default: {
             *out_tag = parse_statement_decoration_none;
             return production_for<plains>();
diff --git a/src/proc.h b/src/proc.h
index c39e1a123..abca58465 100644
--- a/src/proc.h
+++ b/src/proc.h
@@ -36,6 +36,8 @@ enum class process_type_t {
     block_node,
     /// The exec builtin.
     exec,
+    /// A literal evaluation
+    eval,
 };
 
 enum class job_control_t {