[Clang] Fix a crash when parsing an invalid decltype

[cor3ntin]

We would try to exact an annotated token before checking if it was valid, leading to a crash when decltype was the only token that was parsed (which can happen in the absense of opening paren)

Fixes #114815

[llvmbot]

@llvm/pr-subscribers-clang

Author: Corentin Jabot (cor3ntin)

Changes

We would try to exact an annotated token before checking if it was valid, leading to a crash when decltype was the only token that was parsed (which can happen in the absense of opening paren)

Fixes #114815

---

Full diff: https://github.com/llvm/llvm-project/pull/148798.diff

2 Files Affected:

• (modified) clang/lib/Parse/ParseDeclCXX.cpp (+3-3)
• (added) clang/test/Parser/gh114815.cpp (+6)

diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 59e6e0af4b5b0..5bdc13d75a9e1 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -1132,14 +1132,14 @@ void Parser::AnnotateExistingDecltypeSpecifier(const DeclSpec &DS,
                                                SourceLocation EndLoc) {
   // make sure we have a token we can turn into an annotation token
   if (PP.isBacktrackEnabled()) {
-    PP.RevertCachedTokens(1);
-    if (DS.getTypeSpecType() == TST_error) {
+    if (DS.getTypeSpecType() == TST_error)
       // We encountered an error in parsing 'decltype(...)' so lets annotate all
       // the tokens in the backtracking cache - that we likely had to skip over
       // to get to a token that allows us to resume parsing, such as a
       // semi-colon.
       EndLoc = PP.getLastCachedTokenLocation();
-    }
+    else
+      PP.RevertCachedTokens(1);
   } else
     PP.EnterToken(Tok, /*IsReinject*/ true);
 
diff --git a/clang/test/Parser/gh114815.cpp b/clang/test/Parser/gh114815.cpp
new file mode 100644
index 0000000000000..6a89384e9e66d
--- /dev/null
+++ b/clang/test/Parser/gh114815.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -verify %s -std=c++11 -fsyntax-only
+
+#define ID(X) X
+extern int ID(decltype);
+// expected-error@-1 {{expected '(' after 'decltype'}} \
+// expected-error@-1 {{expected unqualified-id}}

[shafik]

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