From 75db3b4ff488fb14c4fbd5bfccddfd328cd192f1 Mon Sep 17 00:00:00 2001
From: Aaron Gyes <me@aaron.gy>
Date: Thu, 11 Apr 2019 14:28:27 -0700
Subject: [PATCH] fix incorrectly aligned carat in command expansion errors and
 more

- fix the carat position expanding e.g. `command $,`
- improve the error reporting for not-allowed command subtitutions
  by figuring out where the expansion failed instead of using
  SOURCE_LOCATION_UNKNOWN
- allow nullptr for parse_util_licate_brackets_range() out_string
  argument if we don't need it to do any work.

Fixes #5812
---
 src/expand.cpp     | 17 ++++++++++-------
 src/parse_util.cpp |  7 +++++--
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/expand.cpp b/src/expand.cpp
index 7d73ff3ca..079f0199f 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -879,13 +879,16 @@ static expand_error_t expand_stage_cmdsubst(wcstring input, std::vector<completi
                                             parse_error_list_t *errors) {
     UNUSED(vars);
     if (EXPAND_SKIP_CMDSUBST & flags) {
-        wchar_t *begin, *end;
-        if (parse_util_locate_cmdsubst(input.c_str(), &begin, &end, true) == 0) {
-            append_completion(out, std::move(input));
-        } else {
-            append_cmdsub_error(errors, SOURCE_LOCATION_UNKNOWN,
-                                L"Command substitutions not allowed");
-            return EXPAND_ERROR;
+        size_t cur = 0, start = 0, end;
+        switch (parse_util_locate_cmdsubst_range(input, &cur, nullptr, &start, &end, true)) {
+            case 0:
+                append_completion(out, std::move(input));
+                break;
+            case 1: /* fallthroughs intentional */
+               append_cmdsub_error(errors, start, L"Command substitutions not allowed");
+            case -1:
+            default:
+                return EXPAND_ERROR;
         }
     } else {
         bool cmdsubst_ok = expand_cmdsubst(std::move(input), out, errors);
diff --git a/src/parse_util.cpp b/src/parse_util.cpp
index 5d8fe3cc8..2a0054513 100644
--- a/src/parse_util.cpp
+++ b/src/parse_util.cpp
@@ -185,7 +185,7 @@ static int parse_util_locate_brackets_range(const wcstring &str, size_t *inout_c
                                             size_t *out_end, bool accept_incomplete,
                                             wchar_t open_type, wchar_t close_type) {
     // Clear the return values.
-    out_contents->clear();
+    if (out_contents != nullptr) out_contents->clear();
     *out_start = 0;
     *out_end = str.size();
 
@@ -213,7 +213,9 @@ static int parse_util_locate_brackets_range(const wcstring &str, size_t *inout_c
 
     // Assign the substring to the out_contents.
     const wchar_t *interior_begin = bracket_range_begin + 1;
-    out_contents->assign(interior_begin, bracket_range_end - interior_begin);
+    if (out_contents != nullptr) {
+        out_contents->assign(interior_begin, bracket_range_end - interior_begin);
+    }
 
     // Return the start and end.
     *out_start = bracket_range_begin - buff;
@@ -1134,6 +1136,7 @@ static bool detect_errors_in_plain_statement(const wcstring &buff_src,
         if (expand_to_command_and_args(*unexp_command, null_environment_t{}, &command, nullptr,
                                        parse_errors) == EXPAND_ERROR) {
             errored = true;
+            parse_error_offset_source_start(parse_errors, source_start);
         }
 
         // Check that pipes are sound.