commit c051763d52066d8421a41015a8d49b5db8d3fb36
author brettw <brettw@chromium.org> Wed Jul 13 14:29:23 2016 -0700
committer Commit bot <commit-bot@chromium.org> Wed Jul 13 21:32:31 2016 +0000
tree 08c125e262536a7d19a479635cabb15a30c5a428
parent 9238fa1cf7ed2bd8f1a2c16c1241f906a149458b

Mark build arguments implicitly used in GN.

This regressed in https://codereview.chromium.org/2092623002 which caused a revert of the GN roll. The particular issue is that a build argument in a BUILD.gn file was used in only one of the toolchains, so the other toolchains were giving unused variable errors on it.

Build variables kept at their default values already are marked implicitly used, and anything in a .gni file is the same. The remaining cases are pretty confusing so it seems better to not warn in this case instead of requiring the author to wrap the build variable in a condition based on the usage.

TBR=dpranke

Review-Url: https://codereview.chromium.org/2151633002
Cr-Original-Commit-Position: refs/heads/master@{#405291}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 8b05f575431f4854163470695cf1a6f6495263ce

tools/gn/args.cc

diff --git a/tools/gn/args.cc b/tools/gn/args.cc
index accdf7e..823a8cc 100644
--- a/tools/gn/args.cc
+++ b/tools/gn/args.cc
@@ -184,6 +184,12 @@
       declared_arguments.insert(arg);
     }
 
+    // In all the cases below, mark the variable used. If a variable is set
+    // that's only used in one toolchain, we don't want to report unused
+    // variable errors in other toolchains. Also, in some cases it's reasonable
+    // for the build file to overwrite the value with a different value based
+    // on some other condition without dereferencing the value first.
+
     // Check whether this argument has been overridden on the toolchain level
     // and use the override instead.
     Scope::KeyValueMap::const_iterator toolchain_override =
@@ -192,6 +198,7 @@
       scope_to_set->SetValue(toolchain_override->first,
                              toolchain_override->second,
                              toolchain_override->second.origin());
+      scope_to_set->MarkUsed(arg.first);
       continue;
     }
 
@@ -201,11 +208,10 @@
     if (override != overrides_.end()) {
       scope_to_set->SetValue(override->first, override->second,
                              override->second.origin());
+      scope_to_set->MarkUsed(override->first);
       continue;
     }
 
-    // Mark the variable used so the build script can override it in
-    // certain cases without getting unused value errors.
     scope_to_set->SetValue(arg.first, arg.second, arg.second.origin());
     scope_to_set->MarkUsed(arg.first);
   }