[PATCH] D90303: [ASTMatchers] Made isExpandedFromMacro Polymorphic

[Nathan James via Phabricator via cfe-commits]

njames93 added inline comments.


================
Comment at: clang/include/clang/ASTMatchers/ASTMatchers.h:313
+                          AST_POLYMORPHIC_SUPPORTED_TYPES(Decl, Stmt, TypeLoc),
+                          std::string, MacroName) {
   // Verifies that the statement' beginning and ending are both expanded from
----------------
aaron.ballman wrote:
> You mentioned that the change from `StringRef` to `std::string` was to avoid lifetime issues while matching, but I'm wondering if you can expound on that situation a bit more. I would have assumed that any memoization that involves `StringRef` would be responsible for the lifetime issues rather than the matchers themselves, but maybe I'm thinking about a different way you can hit lifetime issues than you are.
Take this as contrived, however using ASAN reports a heap-use-after-free for this code when isExpandedFromMacro takes a `StringRef` but works fine when using `std::string`.
```lang=c++
TEST(IsExpandedFromMacro, IsExpandedFromMacro_MatchesDecls) {
  auto Matcher = isExpandedFromMacro(std::string("MY_MACRO_OVERFLOW_SMALL_STRING_SIZE"));// <-Temporary string created and destroyed here.
  StringRef input = R"cc(
#define MY_MACRO_OVERFLOW_SMALL_STRING_SIZE(a) int i = a;
    void Test() { MY_MACRO_OVERFLOW_SMALL_STRING_SIZE(4); }
  )cc";
  EXPECT_TRUE(matches(input, varDecl(Matcher))); // <- heap-use-after-free detected down the callstack from here.
}
```
Obviously this is very contrived to ensure asan detects the use-after-free and to ensure the temporary string is destroyed before the matcher. For these tests it doesn't look like a problem, but in other instances these matchers will outlive a string being passed to them
```lang=c++
void addVarFromMacro(ASTMatchFinder* Finder, std::string MacroName) {
  Finder->addMatcher(varDecl(isExpandedFromMacro(MacroName)), this);
}
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D90303/new/

https://reviews.llvm.org/D90303