[clang] [clang-scan-deps] Fix "unterminated conditional directive" bug (PR #146645)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ziqing Luo (ziqingluo-90)

<details>
<summary>Changes</summary>

`clang-scan-deps` threw "unterminated conditional directive" error falsely on the following example:

```
#ifndef __TEST
#define __TEST

#if defined(__TEST_DUMMY)
 #if defined(__TEST_DUMMY2)
  #pragma GCC warning                                                          \
      "Hello!"
 #else
  #pragma GCC error                                                            \
      "World!"
 #endif // defined(__TEST_DUMMY2)
#endif  // defined(__TEST_DUMMY)

#endif // #ifndef __TEST
```

The issue comes from PR #<!-- -->143950, where the flag `LastNonWhitespace` does not correctly represent the state for the example above.  The PR aimed to support that a line-continuation can be followed by whitespaces.  This fix uses a more straightforward but less efficient way to do the same thing---it looks back for a line-continuation and skips any number of whitespaces before that.

rdar://153742186

---
Full diff: https://github.com/llvm/llvm-project/pull/146645.diff


2 Files Affected:

- (modified) clang/lib/Lex/DependencyDirectivesScanner.cpp (+21-8) 
- (modified) clang/unittests/Lex/DependencyDirectivesScannerTest.cpp (+31) 


``````````diff
diff --git a/clang/lib/Lex/DependencyDirectivesScanner.cpp b/clang/lib/Lex/DependencyDirectivesScanner.cpp
index 1b6b16c561141..b1f1285bd959d 100644
--- a/clang/lib/Lex/DependencyDirectivesScanner.cpp
+++ b/clang/lib/Lex/DependencyDirectivesScanner.cpp
@@ -393,7 +393,7 @@ static bool isQuoteCppDigitSeparator(const char *const Start,
 }
 
 void Scanner::skipLine(const char *&First, const char *const End) {
-  char LastNonWhitespace = ' ';
+  const char * const OldFirst = First;
   for (;;) {
     assert(First <= End);
     if (First == End)
@@ -419,8 +419,6 @@ void Scanner::skipLine(const char *&First, const char *const End) {
       // Iterate over comments correctly.
       if (*First != '/' || End - First < 2) {
         LastTokenPtr = First;
-        if (!isWhitespace(*First))
-          LastNonWhitespace = *First;
         ++First;
         continue;
       }
@@ -433,8 +431,6 @@ void Scanner::skipLine(const char *&First, const char *const End) {
 
       if (First[1] != '*') {
         LastTokenPtr = First;
-        if (!isWhitespace(*First))
-          LastNonWhitespace = *First;
         ++First;
         continue;
       }
@@ -446,9 +442,26 @@ void Scanner::skipLine(const char *&First, const char *const End) {
       return;
 
     // Skip over the newline.
-    skipNewline(First, End);
-
-    if (LastNonWhitespace != '\\')
+    auto Len = skipNewline(First, End);
+    // Since P2223R2 allows the line-continuation slash \ to be followed by
+    // additional whitespace, we need to check that here if `First`
+    // follows a `\\` and whitespaces.
+
+    // `LookBack` points to the character before the newline:
+    const char *LookBack = First - Len;
+    bool LineContinuationFound = false;
+
+    // Move `LookBack` backwards to find line-continuation and whitespaces:
+    while (LookBack >= OldFirst) { // bound `LookBack` by `OldFirst`:
+      if (isWhitespace(*LookBack)) {
+        --LookBack; // whitespace before '\\' is ok
+        continue;
+      }
+      if (*LookBack == '\\')
+        LineContinuationFound = true;
+      break; // not a whitespace, end loop
+    }
+    if (!LineContinuationFound)
       break;
   }
 }
diff --git a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
index 61f74929c1e98..4f64ed80cb7bf 100644
--- a/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
+++ b/clang/unittests/Lex/DependencyDirectivesScannerTest.cpp
@@ -880,6 +880,37 @@ TEST(MinimizeSourceToDependencyDirectivesTest,
   EXPECT_EQ(pp_eof, Directives[22].Kind);
 }
 
+TEST(MinimizeSourceToDependencyDirectivesTest,
+     TestFixedBugThatReportUnterminatedDirectiveFalsely) {
+  SmallVector<char, 512> Out;
+  SmallVector<dependency_directives_scan::Token, 16> Tokens;
+  SmallVector<Directive, 16> Directives;
+
+  StringRef Input = "#ifndef __TEST \n"
+                    "#define __TEST \n"
+                    "#if defined(__TEST_DUMMY) \n"
+                    "#if defined(__TEST_DUMMY2) \n"
+                    "#pragma GCC warning        \\ \n"
+                    "\"hello!\"\n"
+                    "#else\n"
+                    "#pragma GCC error          \\ \n"
+                    "\"world!\" \n"
+                    "#endif // defined(__TEST_DUMMY2) \n"
+                    "#endif  // defined(__TEST_DUMMY) \n"
+                    "#endif // #ifndef __TEST \n";
+  ASSERT_FALSE( // False on no error:
+      minimizeSourceToDependencyDirectives(Input, Out, Tokens, Directives));
+  ASSERT_TRUE(Directives.size() == 8);
+  EXPECT_EQ(pp_ifndef, Directives[0].Kind);
+  EXPECT_EQ(pp_define, Directives[1].Kind);
+  EXPECT_EQ(pp_if, Directives[2].Kind);
+  EXPECT_EQ(pp_if, Directives[3].Kind);
+  EXPECT_EQ(pp_endif, Directives[4].Kind);
+  EXPECT_EQ(pp_endif, Directives[5].Kind);
+  EXPECT_EQ(pp_endif, Directives[6].Kind);
+  EXPECT_EQ(pp_eof, Directives[7].Kind);
+}
+
 TEST(MinimizeSourceToDependencyDirectivesTest, PoundWarningAndError) {
   SmallVector<char, 128> Out;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/146645