[clang-tidy] Fix crash in bugprone-not-null-terminated-result check (#160727)

The check was crashing when trying to evaluate value-dependent
expressions using EvaluateAsInt() in cases where the src parameter of
memcpy is value-dependent, but the length is not. Added
isValueDependent() check before EvaluateAsInt() call to prevent the
crash.

Author: gamesh411

clang-tools-extra/clang-tidy/bugprone/NotNullTerminatedResultCheck.cpp

@@ -64,15 +64,17 @@ static unsigned getLength(const Expr *E,
   if (!E)
     return 0;
 
-  Expr::EvalResult Length;
   E = E->IgnoreImpCasts();
 
   if (const auto *LengthDRE = dyn_cast<DeclRefExpr>(E))
     if (const auto *LengthVD = dyn_cast<VarDecl>(LengthDRE->getDecl()))
       if (!isa<ParmVarDecl>(LengthVD))
-        if (const Expr *LengthInit = LengthVD->getInit())
+        if (const Expr *LengthInit = LengthVD->getInit();
+            LengthInit && !LengthInit->isValueDependent()) {
+          Expr::EvalResult Length;
           if (LengthInit->EvaluateAsInt(Length, *Result.Context))
             return Length.Val.getInt().getZExtValue();
+        }
 
   if (const auto *LengthIL = dyn_cast<IntegerLiteral>(E))
     return LengthIL->getValue().getZExtValue();

clang-tools-extra/docs/ReleaseNotes.rst

@@ -274,6 +274,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/narrowing-conversions>` check by fixing
   false positive from analysis of a conditional expression in C.
 
+- Improved :doc:`bugprone-not-null-terminated-result
+  <clang-tidy/checks/bugprone/not-null-terminated-result>` check by fixing
+  a crash caused by certain value-dependent expressions.
+
 - Improved :doc:`bugprone-reserved-identifier
   <clang-tidy/checks/bugprone/reserved-identifier>` check by ignoring
   declarations and macros in system headers.

clang-tools-extra/test/clang-tidy/checkers/bugprone/not-null-terminated-result-value-dependent-crash.cpp

@@ -0,0 +1,23 @@
+// RUN: %check_clang_tidy %s bugprone-not-null-terminated-result %t -- \
+// RUN: -- -std=c++17 -I %S/Inputs/not-null-terminated-result
+
+// This test case reproduces the crash when the check tries to evaluate
+// a value-dependent expression using EvaluateAsInt() in
+// bugprone-not-null-terminated-result, where the src parameter of memcpy is
+// value-dependent, but the length is not.
+
+// expected-no-diagnostics
+
+#include "not-null-terminated-result-cxx.h"
+
+template<size_t N>
+class ValueDependentClass {
+public:
+  void copyData(char* Dst) {
+    const char* Src = reinterpret_cast<const char*>(this);
+    // The length parameter is arbitrary, but the crash is not reproduced if it is N.
+    memcpy(Dst, Src, 32);
+  }
+};
+
+template class ValueDependentClass<42>; // The template parameter value is arbitrary.