[clang] d5be155 - [clang-format] Don't crash on malformed preprocessor conditions

[via cfe-commits]

Author: sstwcw
Date: 2022-10-30T02:18:58Z
New Revision: d5be1550f1406844501ab87a3e92622927a203e0

URL: https://github.com/llvm/llvm-project/commit/d5be1550f1406844501ab87a3e92622927a203e0
DIFF: https://github.com/llvm/llvm-project/commit/d5be1550f1406844501ab87a3e92622927a203e0.diff

LOG: [clang-format] Don't crash on malformed preprocessor conditions

Previously the program would crash on this input:

```
#else
#if X
```

The problem was that in `parsePPElse`, `PPBranchLevel` would be
incremented when the first `#else` gets parsed, but `PPLevelBranchCount`
and `PPLevelBranchIndex` would not be updated together.

I found the problem when working on D135740.

Differential Revision: https://reviews.llvm.org/D135972

Added: 
    

Modified: 
    clang/lib/Format/UnwrappedLineParser.cpp
    clang/unittests/Format/FormatTest.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 25d9018fa1093..0372b89397db9 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1215,9 +1215,12 @@ void UnwrappedLineParser::parsePPElse() {
   // If a potential include guard has an #else, it's not an include guard.
   if (IncludeGuard == IG_Defined && PPBranchLevel == 0)
     IncludeGuard = IG_Rejected;
+  // Don't crash when there is an #else without an #if.
+  assert(PPBranchLevel >= -1);
+  if (PPBranchLevel == -1)
+    conditionalCompilationStart(/*Unreachable=*/true);
   conditionalCompilationAlternative();
-  if (PPBranchLevel > -1)
-    --PPBranchLevel;
+  --PPBranchLevel;
   parsePPUnknown();
   ++PPBranchLevel;
 }

diff  --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 69bd39590589f..e2eced46c3b4b 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -5193,6 +5193,34 @@ TEST_F(FormatTest, MacroDefinitionsWithIncompleteCode) {
   verifyNoCrash("a={0,1\n#if a\n#else\n;\n#endif\n}");
   verifyNoCrash("#if a\na(\n#else\n#endif\n) a {a,b,c,d,f,g};");
   verifyNoCrash("#ifdef A\n a(\n #else\n #endif\n) = []() {      \n)}");
+  verifyNoCrash("#else\n"
+                "#else\n"
+                "#endif\n"
+                "#endif");
+  verifyNoCrash("#else\n"
+                "#if X\n"
+                "#endif\n"
+                "#endif");
+  verifyNoCrash("#else\n"
+                "#endif\n"
+                "#if X\n"
+                "#endif");
+  verifyNoCrash("#if X\n"
+                "#else\n"
+                "#else\n"
+                "#endif\n"
+                "#endif");
+  verifyNoCrash("#if X\n"
+                "#elif Y\n"
+                "#elif Y\n"
+                "#endif\n"
+                "#endif");
+  verifyNoCrash("#endif\n"
+                "#endif");
+  verifyNoCrash("#endif\n"
+                "#else");
+  verifyNoCrash("#endif\n"
+                "#elif Y");
 }
 
 TEST_F(FormatTest, MacrosWithoutTrailingSemicolon) {