[clang-tools-extra] [clang-tidy] Fix crash in C language in readability-non-const-parameter (PR #100461)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL created https://github.com/llvm/llvm-project/pull/100461

Fix crash that happen when redeclaration got
different number of parameters than definition.

No release notes, as this will be backported.

Fixes #100340



>From 253e132b022a4f2b454869eed416fd6966f35dd3 Mon Sep 17 00:00:00 2001
From: Piotr Zegar <me at piotrzegar.pl>
Date: Wed, 24 Jul 2024 20:20:37 +0000
Subject: [PATCH] [clang-tidy] Fix crash in C language in
 readability-non-const-parameter

Fix crash that happen when redeclaration got
diffrent number of parameters than definition.

Fixes #100340
---
 .../clang-tidy/readability/NonConstParameterCheck.cpp |  5 ++++-
 .../checkers/readability/non-const-parameter.c        | 11 +++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 clang-tools-extra/test/clang-tidy/checkers/readability/non-const-parameter.c

diff --git a/clang-tools-extra/clang-tidy/readability/NonConstParameterCheck.cpp b/clang-tools-extra/clang-tidy/readability/NonConstParameterCheck.cpp
index 95a3a5165e2e8..43b69a24bdb16 100644
--- a/clang-tools-extra/clang-tidy/readability/NonConstParameterCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/NonConstParameterCheck.cpp
@@ -157,9 +157,12 @@ void NonConstParameterCheck::diagnoseNonConstParameters() {
     if (!Function)
       continue;
     unsigned Index = Par->getFunctionScopeIndex();
-    for (FunctionDecl *FnDecl : Function->redecls())
+    for (FunctionDecl *FnDecl : Function->redecls()) {
+      if (FnDecl->getNumParams() <= Index)
+        continue;
       Fixes.push_back(FixItHint::CreateInsertion(
           FnDecl->getParamDecl(Index)->getBeginLoc(), "const "));
+    }
 
     diag(Par->getLocation(), "pointer parameter '%0' can be pointer to const")
         << Par->getName() << Fixes;
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/non-const-parameter.c b/clang-tools-extra/test/clang-tidy/checkers/readability/non-const-parameter.c
new file mode 100644
index 0000000000000..db50467f3dd94
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/non-const-parameter.c
@@ -0,0 +1,11 @@
+// RUN: %check_clang_tidy %s readability-non-const-parameter %t
+
+static int f();
+
+int f(p)
+  int *p;
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: pointer parameter 'p' can be pointer to const [readability-non-const-parameter]
+// CHECK-FIXES: {{^}}  const int *p;{{$}}
+{
+    return *p;
+}