[clang-tidy] Fix a crash in bugprone-not-null-terminated-result check when `__STDC_WANT_LIB_EXT1__` was undefined after definition.

[ArcsinX]

Summary

PP->getMacroInfo() returns nullptr for undefined macro, so we need to check this return value before dereference.
Stack dump:

#0 0x0000000002185e6a llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/llvm-project/build/bin/clang-tidy+0x2185e6a)
#1 0x0000000002183e8c llvm::sys::RunSignalHandlers() (/llvm-project/build/bin/clang-tidy+0x2183e8c)
#2 0x0000000002183ff3 SignalHandler(int) (/llvm-project/build/bin/clang-tidy+0x2183ff3)
#3 0x00007f37df9b1390 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x11390)
#4 0x000000000052054e clang::tidy::bugprone::NotNullTerminatedResultCheck::check(clang::ast_matchers::MatchFinder::MatchResult const&) (/llvm-project/build/bin/clang-tidy+0x52054e)

[hokein]

clang-tools-extra/test/clang-tidy/checkers/bugprone-not-null-terminated-result-undef-stdc-want-lib-ext1.c

4

The same here.

[Eugene.Zelenko]

clang-tools-extra/test/clang-tidy/checkers/bugprone-not-null-terminated-result-undef-stdc-want-lib-ext1.c

18

Please add newline.

[ArcsinX]

newline

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

void NotNullTerminatedResultCheck::check(
 
   if (WantToUseSafeFunctions && PP->isMacroDefined("__STDC_LIB_EXT1__")) {
     Optional<bool> AreSafeFunctionsWanted;
 
     Preprocessor::macro_iterator It = PP->macro_begin();
     while (It != PP->macro_end() && !AreSafeFunctionsWanted.hasValue()) {
       if (It->first->getName() == "__STDC_WANT_LIB_EXT1__") {
         const auto *MI = PP->getMacroInfo(It->first);
+        // PP->getMacroInfo() returns nullptr if macro has no definition.
+        if (MI) {
           const auto &T = MI->tokens().back();
           StringRef ValueStr = StringRef(T.getLiteralData(), T.getLength());
           llvm::APInt IntValue;
           ValueStr.getAsInteger(10, IntValue);
           AreSafeFunctionsWanted = IntValue.getZExtValue();
         }
+      }
 
       ++It;
     }
 
     if (AreSafeFunctionsWanted.hasValue())
       UseSafeFunctions = AreSafeFunctionsWanted.getValue();
   }
 

clang-tools-extra/test/clang-tidy/checkers/bugprone-not-null-terminated-result-undef-stdc-want-lib-ext1.c

+// RUN: %check_clang_tidy %s bugprone-not-null-terminated-result %t -- \
+// RUN: -- -std=c11 -I %S/Inputs/bugprone-not-null-terminated-result
+
+#include "not-null-terminated-result-c.h"
+
+#define __STDC_LIB_EXT1__ 1
+#define __STDC_WANT_LIB_EXT1__ 1
+#undef __STDC_WANT_LIB_EXT1__
+
+void f(const char *src) {
+  char dest[13];
+  memcpy_s(dest, 13, src, strlen(src) - 1);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: the result from calling 'memcpy_s' is not null-terminated [bugprone-not-null-terminated-result]
+  // CHECK-FIXES: char dest[14];
+  // CHECK-FIXES-NEXT: strncpy_s(dest, 14, src, strlen(src) - 1);
+}
+