[clang] [clang] Add LangOpts.ScanDeps to fix #88896 (PR #158420)

[Yifan Fang via cfe-commits]

https://github.com/tsfn created https://github.com/llvm/llvm-project/pull/158420

None

>From fa5a534fb56d6ca9fe92e9df7cc86cd76ef5c58d Mon Sep 17 00:00:00 2001
From: Yifan Fang <gat...@gmail.com>
Date: Sat, 13 Sep 2025 18:20:17 +0800
Subject: [PATCH] [clang] Add LangOpts.ScanDeps to fix #88896

---
 clang/include/clang/Basic/LangOptions.def        |  2 ++
 clang/lib/Lex/DependencyDirectivesScanner.cpp    |  1 +
 clang/lib/Lex/Lexer.cpp                          |  2 +-
 .../Lex/DependencyDirectivesScannerTest.cpp      | 16 ++++++++++++++++
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/clang/include/clang/Basic/LangOptions.def 
b/clang/include/clang/Basic/LangOptions.def
index 84f5ab3443a59..7418181472977 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -438,6 +438,8 @@ LANGOPT(CXXAssumptions, 1, 1, NotCompatible, "Enable or 
disable codegen and comp
 
 LANGOPT(RawStringLiterals, 1, 1, NotCompatible, "Enable or disable raw string 
literals")
 
+LANGOPT(ScanDeps, 1, 0, NotCompatible, "True if we are scanning by 
DependencyDirectivesScanner")
+
 ENUM_LANGOPT(StrictFlexArraysLevel, StrictFlexArraysLevelKind, 2,
              StrictFlexArraysLevelKind::Default, NotCompatible,
              "Rely on strict definition of flexible arrays")
diff --git a/clang/lib/Lex/DependencyDirectivesScanner.cpp 
b/clang/lib/Lex/DependencyDirectivesScanner.cpp
index eee57c786442a..81f7c2edb66cc 100644
--- a/clang/lib/Lex/DependencyDirectivesScanner.cpp
+++ b/clang/lib/Lex/DependencyDirectivesScanner.cpp
@@ -74,6 +74,7 @@ struct Scanner {
     LangOpts.ObjC = true;
     LangOpts.LineComment = true;
     LangOpts.RawStringLiterals = true;
+    LangOpts.ScanDeps = true;
     // FIXME: we do not enable C11 or C++11, so we are missing u/u8/U"".
     return LangOpts;
   }
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index b282a600c0e56..e7bf8afb1f835 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -2087,7 +2087,7 @@ bool Lexer::LexNumericConstant(Token &Result, const char 
*CurPtr) {
   }
 
   // If we have a digit separator, continue.
-  if (C == '\'' && (LangOpts.CPlusPlus14 || LangOpts.C23)) {
+  if (C == '\'' && (LangOpts.CPlusPlus14 || LangOpts.C23 || 
LangOpts.ScanDeps)) {
     auto [Next, NextSize] = getCharAndSizeNoWarn(CurPtr + Size, LangOpts);
     if (isAsciiIdentifierContinue(Next)) {
       if (!isLexingRawMode())
diff --git a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp 
b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
index ddc87921ea084..dd8ef8daef816 100644
--- a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
+++ b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
@@ -7,6 +7,7 @@
 
//===----------------------------------------------------------------------===//
 
 #include "clang/Lex/DependencyDirectivesScanner.h"
+#include "clang/Basic/TokenKinds.h"
 #include "llvm/ADT/SmallString.h"
 #include "gtest/gtest.h"
 
@@ -1000,6 +1001,21 @@ int z = 128'78;
   EXPECT_STREQ("#include <test.h>\n", Out.data());
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest, CharacterLiteralInPreprocessor) 
{
+  SmallVector<char, 128> Out;
+  SmallVector<dependency_directives_scan::Token, 8> Tokens;
+  SmallVector<Directive, 4> Directives;
+
+  StringRef Source = R"(
+    #if 1'2 == 12
+    #endif
+    )";
+  ASSERT_FALSE(minimizeSourceToDependencyDirectives(Source, Out, Tokens, 
Directives));
+  ASSERT_GE(Tokens.size(), 4u);
+  EXPECT_EQ(Tokens[2].Kind, tok::numeric_constant);
+  EXPECT_EQ(Tokens[3].Kind, tok::equalequal);
+}
+
 TEST(MinimizeSourceToDependencyDirectivesTest, PragmaOnce) {
   SmallVector<char, 128> Out;
   SmallVector<dependency_directives_scan::Token, 4> Tokens;

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