commit 3d0d3445f67d91be25ffdc9ba9b352b9af9cf07e
author David 'Digit' Turner <digit@google.com> Mon Mar 03 14:00:03 2025 +0100
committer GN LUCI <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Mar 03 07:54:53 2025 -0800
tree 124a4d5a4c5d0a59995f011707287a82506ea331
parent 4a8016dc391553fa1644c0740cc04eaac844121e

Remove obsolete debug checks.

Now that stamp files are replaced by phony Ninja targets, it is
perfectly possible for a target to not generate any Ninja rule,
so remove a DCHECK() call that caused a debug version of GN to
assert at runtime when processing a Chromium build graph.

Also remove a NOTREACHED() statement when expanding C++ specific
substitution expressions (e.g. {{cflags}} or {{include_dirs}})
that are used in action() targets, such as those expanded by
the nocompile_source_set() Chromium template. This also caused
the debug version of GN to assert at runtime.

Comparison of the generated Ninja build plan after/before this
CL shows no difference for a regular Chromium Linux/x64
configuration.

Fixed: 388100196
Change-Id: Iebc465517ea866cb35b724080058f995f885597b
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/18280
Commit-Queue: David Turner <digit@google.com>
Reviewed-by: Takuto Ikuta <tikuta@google.com>

src/gn/command_gen.cc

diff --git a/src/gn/command_gen.cc b/src/gn/command_gen.cc
index ac94487..f997086 100644
--- a/src/gn/command_gen.cc
+++ b/src/gn/command_gen.cc
@@ -109,12 +109,12 @@
   std::string rule =
       NinjaTargetWriter::RunAndWriteFile(target, resolved, ninja_outputs);
 
-  DCHECK(!rule.empty());
-
   {
     std::lock_guard<std::mutex> lock(write_info->lock);
-    write_info->rules[target->toolchain()].emplace_back(target,
-                                                        std::move(rule));
+    if (!rule.empty()) {
+      write_info->rules[target->toolchain()].emplace_back(target,
+                                                          std::move(rule));
+    }
 
     if (write_info->want_ninja_outputs) {
       write_info->ninja_outputs_map.emplace(target,

src/gn/substitution_writer.cc

diff --git a/src/gn/substitution_writer.cc b/src/gn/substitution_writer.cc
index c9624d7..a1f0254 100644
--- a/src/gn/substitution_writer.cc
+++ b/src/gn/substitution_writer.cc
@@ -384,8 +384,10 @@
   } else if (IsValidRustSubstitution(type)) {
     to_rebase = source.value();
   } else {
-    NOTREACHED() << "Unsupported substitution for this function: "
-                 << type->name;
+    // Do not add NOTREACHED() statement here, as Chromium
+    // nobuild_source_set() templates rely on passing {{cflags}}
+    // substitution expressions (and other C++ specific ones)
+    // to action_foreach(). See https://gn.issues.chromium.org/388100196.
     return std::string();
   }