[clang-tidy] Initialize boolean variables with 'false' in cppcoreguidelines-init-variables' fix-it

[SimplyDanny]

Summary

In case of a variable with a built-in boolean type, false is a better fit to default-initialize it.

[SimplyDanny]

This is a potential fix for this issue.

[njames93]

Can you add a line to release notes about this fix then LGTM

[SimplyDanny]

In D129420#3640482, @njames93 wrote:

Can you add a line to release notes about this fix then LGTM

Sure. Thank you for the fast review!

[njames93]

clang-tools-extra/docs/ReleaseNotes.rst

188

It should live here instead.

250–253

Sorry I should've mentioned, we keep this list in alphabetical order(for the names of the checks).
Can you push a patch to move this into its correct place(no need for a review and commit as NFC)

[SimplyDanny]

clang-tools-extra/docs/ReleaseNotes.rst

250–253

Ah sorry. I could have noticed that. Fixed in this commit.

clang-tools-extra/clang-tidy/cppcoreguidelines/InitVariablesCheck.cpp

if (MatchedDecl->getEndLoc().isMacroID())
     return;
 
   QualType TypePtr = MatchedDecl->getType();
   llvm::Optional<const char *> InitializationString = llvm::None;
   bool AddMathInclude = false;
 
   if (TypePtr->isEnumeralType())
     InitializationString = nullptr;
+  else if (TypePtr->isBooleanType())
+    InitializationString = " = false";
   else if (TypePtr->isIntegerType())
     InitializationString = " = 0";
   else if (TypePtr->isFloatingType()) {
     InitializationString = " = NAN";
     AddMathInclude = true;
   } else if (TypePtr->isAnyPointerType()) {
     if (getLangOpts().CPlusPlus11)
       InitializationString = " = nullptr";

clang-tools-extra/docs/ReleaseNotes.rst

- Fixed bugs in :doc:`bugprone-use-after-move
   - Treat a move in a lambda capture as happening in the function that defines
     the lambda, not within the body of the lambda (as we were previously doing
     erroneously).
 
   - Don't emit an erroneous warning on self-moves.
 
 - Made :doc:`cert-oop57-cpp <clang-tidy/checks/cert/oop57-cpp>` more sensitive
   by checking for an arbitrary expression in the second argument of ``memset``.
 
 - Improved :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>` check.
 
   Fixed an issue when there was already an initializer in the constructor and
   the check would try to create another initializer for the same member.
 
 - Fixed a false positive in :doc:`cppcoreguidelines-virtual-class-destructor
   <clang-tidy/checks/cppcoreguidelines/virtual-class-destructor>` involving

 - Fixed a false positive in :doc:`readability-non-const-parameter
   <clang-tidy/checks/readability/non-const-parameter>` when the parameter is
   referenced by an lvalue.
 
 - Expanded :doc:`readability-simplify-boolean-expr
   <clang-tidy/checks/readability/simplify-boolean-expr>` to simplify expressions
   using DeMorgan's Theorem.
 
+- Made the fix-it of :doc:`cppcoreguidelines-init-variables
+  <clang-tidy/checks/cppcoreguidelines/init-variables>` use ``false`` to initialize
+  boolean variables.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
 Improvements to include-fixer
 -----------------------------
 
 The improvements are...
 

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/init-variables.cpp

void init_unit_tests() {
   float fval = 85.0;
   double d;
   // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: variable 'd' is not initialized [cppcoreguidelines-init-variables]
   // CHECK-FIXES: {{^}}  double d = NAN;{{$}}
   double dval = 99.0;
 
   bool b;
   // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: variable 'b' is not initialized [cppcoreguidelines-init-variables]
-  // CHECK-FIXES: {{^}}  bool b = 0;{{$}}
+  // CHECK-FIXES: {{^}}  bool b = false;{{$}}
   bool bval = true;
 
   const char *ptr;
   // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: variable 'ptr' is not initialized [cppcoreguidelines-init-variables]
   // CHECK-FIXES: {{^}}  const char *ptr = nullptr;{{$}}
   const char *ptrval = "a string";
 
   UnusedStruct u;