[clang-tools-extra] [clang-tidy] Add recursion protection in ExceptionSpecAnalyzer (PR #66810)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL created https://github.com/llvm/llvm-project/pull/66810

Normally endless recursion should not happen in ExceptionSpecAnalyzer, but if AST would be malformed (missing include), this could cause crash.

I run into this issue when due to missing include constructor argument were parsed as FieldDecl.
As checking for recursion cost nothing, why not to do this in check just in case.

>From 1c76d3c37e25048b5aaaeeca8bcb370c9e7c04b7 Mon Sep 17 00:00:00 2001
From: Piotr Zegar <me at piotrzegar.pl>
Date: Tue, 19 Sep 2023 19:05:00 +0000
Subject: [PATCH] [clang-tidy] Add recursion protection in
 ExceptionSpecAnalyzer

Normally endless recursion should not happen in ExceptionSpecAnalyzer,
but if AST would be malformed (missing include), this could cause crash.
---
 .../clang-tidy/utils/ExceptionSpecAnalyzer.cpp      | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/utils/ExceptionSpecAnalyzer.cpp b/clang-tools-extra/clang-tidy/utils/ExceptionSpecAnalyzer.cpp
index 4dd4a95f880aca0..5ffa4a92f574e0b 100644
--- a/clang-tools-extra/clang-tidy/utils/ExceptionSpecAnalyzer.cpp
+++ b/clang-tools-extra/clang-tidy/utils/ExceptionSpecAnalyzer.cpp
@@ -14,13 +14,14 @@ namespace clang::tidy::utils {
 
 ExceptionSpecAnalyzer::State
 ExceptionSpecAnalyzer::analyze(const FunctionDecl *FuncDecl) {
-  // Check if the function has already been analyzed and reuse that result.
-  const auto CacheEntry = FunctionCache.find(FuncDecl);
-  if (CacheEntry == FunctionCache.end()) {
+  // Check if function exist in cache or add temporary value to cache to protect
+  // against endless recursion.
+  const auto [CacheEntry, NotFound] =
+      FunctionCache.try_emplace(FuncDecl, State::NotThrowing);
+  if (NotFound) {
     ExceptionSpecAnalyzer::State State = analyzeImpl(FuncDecl);
-
-    // Cache the result of the analysis.
-    FunctionCache.try_emplace(FuncDecl, State);
+    // Update result with calculated value
+    FunctionCache[FuncDecl] = State;
     return State;
   }