[clang][deps] During scanning don't emit warnings-as-errors that are ignored with diagnostic pragmas.

[vsapsai]

Summary

Before the fix the scanning would fail with
-Werror,-Wnon-modular-include-in-module despite the warning being
suppressed in the source code.

Existing approach with -Wno-error is not sufficient because it negates
only general -Werror but not specific -Werror=... and some warnings
can still emitted as errors. Make the approach stricter by using -w
flag and ignore all warnings, including those upgraded to errors. This
approach is still valid as it doesn't affect the dependencies.

rdar://101588531

[vsapsai]

Should admit that approach with DiagOpts.IgnoreWarnings is pretty blunt but I'm not aware of any reasons to use something more elaborate, like stripping away all -Werror=... flags. So going with a simple change.

[vsapsai]

Ping.

[jansvoboda11]

LGTM, thanks!

[vsapsai]

Thanks for the reviews!

[dyung]

@vsapsai I reverted your change because it was causing the test ClangScanDeps/no-werror.cpp to fail on the PS4/PS5 linux/Windows bots:

• https://lab.llvm.org/buildbot/#/builders/139/builds/31784
• https://lab.llvm.org/buildbot/#/builders/216/builds/13476

[vsapsai]

Ok, I was able to reproduce the error on macOS by adding -target x86_64-sie-ps5 to one of commands in "clang/test/ClangScanDeps/Inputs/no-werror.json" (wouldn't mind receiving PS5 DevKit, by the way). The problem is that Driver::BuildCompilation overwrites DiagnosticsEngine::IgnoreAllWarnings ignoring everything specified in DiagnosticOptions::IgnoreWarnings. Thus we still emit the warning despite asking in DiagnosticOptions not to. D138970 fixes this situation and relies on DiagnosticOptions to set diagnostic options.

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

 }
 
 /// Sanitize diagnostic options for dependency scan.
 static void sanitizeDiagOpts(DiagnosticOptions &DiagOpts) {
   // Don't print 'X warnings and Y errors generated'.
   DiagOpts.ShowCarets = false;
   // Don't write out diagnostic file.
   DiagOpts.DiagnosticSerializationFile.clear();
-  // Don't treat warnings as errors.
-  DiagOpts.Warnings.push_back("no-error");
+  // Don't emit warnings as errors (and all other warnings too).
+  DiagOpts.IgnoreWarnings = true;
 }
 
 /// A clang tool that runs the preprocessor in a mode that's optimized for
 /// dependency scanning for the given compiler invocation.
 class DependencyScanningAction : public tooling::ToolAction {
 public:
   DependencyScanningAction(
       StringRef WorkingDirectory, DependencyConsumer &Consumer,

clang/test/ClangScanDeps/diagnostic-pragmas.c

+// Test scanning deps does not have more errors than the regular compilation.
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+
+// Check the regular compilation does not fail.
+// RUN: %clang -fsyntax-only %t/test.c -I %t/include -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -Wnon-modular-include-in-module -Werror=non-modular-include-in-module
+
+// And now scanning deps should succeed too.
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -j 1
+
+//--- cdb.json.template
+[
+  {
+    "directory": "DIR",
+    "command": "clang -fsyntax-only DIR/test.c -I DIR/include -fmodules -fimplicit-module-maps -fmodules-cache-path=DIR/cache -Wnon-modular-include-in-module -Werror=non-modular-include-in-module",
+    "file": "DIR/test.c"
+  },
+]
+
+//--- include/nonmodular.h
+// empty
+
+//--- include/modular-includer.h
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnon-modular-include-in-module"
+#include <nonmodular.h>
+#pragma clang diagnostic pop
+
+//--- include/module.modulemap
+module ModularIncluder { header "modular-includer.h" }
+
+//--- test.c
+#include <modular-includer.h>