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

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

Fixes llvm#100340

(cherry picked from commit a27f816)

Author: PiotrZSL

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;

clang-tools-extra/docs/ReleaseNotes.rst

@@ -496,6 +496,10 @@ Changes in existing checks
   ``static_cast``. Fixed false positives in C++20 spaceship operator by ignoring
   casts in implicit and defaulted functions.
 
+- Improved :doc:`readability-non-const-parameter
+  <clang-tidy/checks/readability/non-const-parameter>` check to not crash when
+  redeclaration have fewer parameters than expected.
+
 - Improved :doc:`readability-redundant-inline-specifier
   <clang-tidy/checks/readability/redundant-inline-specifier>` check to properly
   emit warnings for static data member with an in-class initializer.

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;
+}