[PATCH] D135972: [clang-format] Don't crash on malformed preprocessor conditions

[sstwcw via Phabricator via cfe-commits]

sstwcw created this revision.
sstwcw added reviewers: HazardyKnusperkeks, MyDeveloperDay, curdeius, owenpan.
sstwcw added a project: clang-format.
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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 <https://reviews.llvm.org/D135740>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135972

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


Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -5193,6 +5193,17 @@
   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)}");
+  std::function<void(std::string, unsigned)> FormatBadBranches =
+      [&](std::string Prefix, unsigned Lines) {
+        const std::string Directives[] = {"", "#if X\n", "#else X\n",
+                                          "#endif\n"};
+        if (Lines == 0)
+          verifyNoCrash(Prefix);
+        else
+          for (const auto &Part : Directives)
+            FormatBadBranches(Prefix + Part, Lines - 1);
+      };
+  FormatBadBranches("", 6);
 }
 
 TEST_F(FormatTest, MacrosWithoutTrailingSemicolon) {
Index: clang/lib/Format/UnwrappedLineParser.cpp
===================================================================
--- clang/lib/Format/UnwrappedLineParser.cpp
+++ clang/lib/Format/UnwrappedLineParser.cpp
@@ -1212,9 +1212,13 @@
   // 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 and #if.
+  if (PPBranchLevel <= -1) {
+    conditionalCompilationStart(/*Unreachable=*/true);
+    assert(PPBranchLevel == 0);
+  }
   conditionalCompilationAlternative();
-  if (PPBranchLevel > -1)
-    --PPBranchLevel;
+  --PPBranchLevel;
   parsePPUnknown();
   ++PPBranchLevel;
 }


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