[clang-scan-deps] Dependency directives source minimizer: handle #pragma once

[arphaman]

Summary

We should re-emit #pragma once to ensure the preprocessor will still honor when running on minimized sources.

[dexonsmith]

LGTM after you add the testcase I mention.

clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp

623

I wondered if it was wrong to ignore extra token on the line, but clang does as well (and emits -Wextra-tokens) so this is fine.

clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp

551–555

Can you also add a test with #pragma once extra tokens? It should get canonicalized to #pragma once.

clang/include/clang/Lex/DependencyDirectivesSourceMinimizer.h

 enum TokenKind {
   pp_none,
   pp_include,
   pp___include_macros,
   pp_define,
   pp_undef,
   pp_import,
   pp_pragma_import,
+  pp_pragma_once,
   pp_include_next,
   pp_if,
   pp_ifdef,
   pp_ifndef,
   pp_elif,
   pp_else,
   pp_endif,
   decl_at_import,

clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp

if (!isVerticalWhitespace(*Last))
     put(' ');
   printDirectiveBody(Last, End);
   First = Last;
   return false;
 }
 
 bool Minimizer::lexPragma(const char *&First, const char *const End) {
   // #pragma.
-  if (!isNextIdentifier("clang", First, End)) {
+  skipWhitespace(First, End);
+  if (First == End || !isIdentifierHead(*First))
+    return false;
+
+  IdInfo FoundId = lexIdentifier(First, End);
+  First = FoundId.Last;
+  if (FoundId.Name == "once") {
+    // #pragma once
+    skipLine(First, End);
+    makeToken(pp_pragma_once);
+    append("#pragma once\n");
+    return false;
+  }
+
+  if (FoundId.Name != "clang") {
     skipLine(First, End);
     return false;
   }
 
   // #pragma clang.
   if (!isNextIdentifier("module", First, End)) {
     skipLine(First, End);
     return false;

clang/unittests/Lex/DependencyDirectivesSourceMinimizerTest.cpp

 int z = 128'78;
 #include <test.h>
 // '
 )";
   ASSERT_FALSE(minimizeSourceToDependencyDirectives(Source, Out));
   EXPECT_STREQ("#include <test.h>\n", Out.data());
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest, PragmaOnce) {
+  SmallVector<char, 128> Out;
+  SmallVector<Token, 4> Tokens;
+
+  StringRef Source = R"(// comment
+#pragma once
+// another comment
+#include <test.h>
+)";
+  ASSERT_FALSE(minimizeSourceToDependencyDirectives(Source, Out, Tokens));
+  EXPECT_STREQ("#pragma once\n#include <test.h>\n", Out.data());
+  ASSERT_EQ(Tokens.size(), 3u);
+  EXPECT_EQ(Tokens[0].K,
+            minimize_source_to_dependency_directives::pp_pragma_once);
+}
+
 } // end anonymous namespace