[clangd] Suppress clang-tidy warnings for code spelled in system macros

[sammccall]

Summary

This aligns with the default behavior of clang-tidy (which we offer no
way to override).

Fixes https://github.com/clangd/clangd/issues/1448

[kadircet]

thanks, lgtm!

[nridge]

clang-tools-extra/clangd/ParsedAST.cpp

545

Why not check CTContext->getOptions().SystemHeaders, since we have ready access to it?

[sammccall]

clang-tools-extra/clangd/ParsedAST.cpp

545

Ah, my mistake, I thought this was some global flag rather than part of tidy options (not sure why I thought that), will fix

clang-tools-extra/clangd/ParsedAST.cpp

 //===--- ParsedAST.cpp -------------------------------------------*- C++-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "ParsedAST.h"
 #include "../clang-tidy/ClangTidyCheck.h"
 #include "../clang-tidy/ClangTidyDiagnosticConsumer.h"
 #include "../clang-tidy/ClangTidyModuleRegistry.h"
 #include "AST.h"
-#include "ASTSignals.h"
 #include "Compiler.h"
 #include "Config.h"
 #include "Diagnostics.h"
 #include "Feature.h"
 #include "FeatureModule.h"
 #include "Headers.h"
 #include "HeuristicResolver.h"
 #include "IncludeCleaner.h"
ASTDiags.setLevelAdjuster([&](DiagnosticsEngine::Level DiagLevel,
           if (IsInsideMainFile && CTContext->shouldSuppressDiagnostic(
                                       DiagLevel, Info, TidySuppressedErrors,
                                       /*AllowIO=*/false,
                                       /*EnableNolintBlocks=*/true)) {
             // FIXME: should we expose the suppression error (invalid use of
             // NOLINT comments)?
             return DiagnosticsEngine::Ignored;
           }
+          // Match behavior for clang-tidy --system-headers=0 (the default).
+          if (Info.hasSourceManager() &&
+              Info.getSourceManager().isInSystemMacro(Info.getLocation()))
+            return DiagnosticsEngine::Ignored;
 
           // Check for warning-as-error.
           if (DiagLevel == DiagnosticsEngine::Warning &&
               CTContext->treatAsError(CheckName)) {
             return DiagnosticsEngine::Error;
           }
         }
       }

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

EXPECT_THAT(
       *TU.build().getDiagnostics(),
       ifTidyChecks(UnorderedElementsAre(::testing::AllOf(
           Diag(Main.range(), "result of integer division used in a floating "
                              "point context; possible loss of precision"),
           diagSource(Diag::ClangTidy),
           diagName("bugprone-integer-division")))));
 }
 
+TEST(DiagnosticTest, ClangTidySystemMacro) {
+  Annotations Main(R"cpp(
+    #include "user.h"
+    #include "system.h"
+    int i = 3;
+    double x = $inline[[8]] / i;
+    double y = $user[[DIVIDE_USER]](i);
+    double z = DIVIDE_SYS(i);
+  )cpp");
+
+  auto TU = TestTU::withCode(Main.code());
+  TU.AdditionalFiles["user.h"] = R"cpp(
+    #define DIVIDE_USER(Y) 8/Y
+  )cpp";
+  TU.AdditionalFiles["system.h"] = R"cpp(
+    #pragma clang system_header
+    #define DIVIDE_SYS(Y) 8/Y
+  )cpp";
+
+  TU.ClangTidyProvider = addTidyChecks("bugprone-integer-division");
+  std::string BadDivision = "result of integer division used in a floating "
+                            "point context; possible loss of precision";
+
+  // Expect to see warning from user macros, but not system macros.
+  // This matches clang-tidy --system-headers=0 (the default).
+  EXPECT_THAT(*TU.build().getDiagnostics(),
+              ifTidyChecks(
+                  UnorderedElementsAre(Diag(Main.range("inline"), BadDivision),
+                                       Diag(Main.range("user"), BadDivision))));
+}
+
 TEST(DiagnosticTest, ClangTidyWarningAsError) {
   Annotations Main(R"cpp(
     int main() {
       int i = 3;
       double f = [[8]] / i; // error-ok
     }
   )cpp");
   TestTU TU = TestTU::withCode(Main.code());