[clang-tidy] Don't warn implicit variables in peformance-unnecessary-copy-initialization.

[hokein]

Summary

[clang-tidy] Don't warn implicit variables in peformance-unnecessary-copy-initialization.

This will prevent the check warning the variables which have been
implicitly added by compiler, like the following case (in for-range loop):

the variable '__end' is copy-constructed from a const reference...

[hokein]

Don't mess up with other patches.

[hokein]

friendly ping.

[alexfh]

LG. Sorry for the delay.

clang-tidy/performance/UnnecessaryCopyInitialization.cpp

auto ConstRefReturningFunctionCall =
                unless(callee(cxxMethodDecl())));
 
   auto localVarCopiedFrom = [](const internal::Matcher<Expr> &CopyCtorArg) {
     return compoundStmt(
                forEachDescendant(
                    declStmt(
                        has(varDecl(hasLocalStorage(),
                                    hasType(matchers::isExpensiveToCopy()),
+                                   unless(isImplicit()),
                                    hasInitializer(
                                        cxxConstructExpr(
                                            hasDeclaration(cxxConstructorDecl(
                                                isCopyConstructor())),
                                            hasArgument(0, CopyCtorArg))
                                            .bind("ctorCall")))
                                .bind("newVarDecl"))).bind("declStmt")))
         .bind("blockStmt");

test/clang-tidy/performance-unnecessary-copy-initialization.cpp

void NegativeLocalCopyWeirdNonCopy() {
   WeirdCopyCtorType neg_weird_2(orig, true);
 }
 void WarningOnlyMultiDeclStmt() {
   ExpensiveToCopyType orig;
   ExpensiveToCopyType copy = orig, copy2;
   // CHECK-MESSAGES: [[@LINE-1]]:23: warning: local copy 'copy' of the variable 'orig' is never modified; consider avoiding the copy [performance-unnecessary-copy-initialization]
   // CHECK-FIXES: ExpensiveToCopyType copy = orig, copy2;
 }
+
+class Element {};
+class Container {
+public:
+  class Iterator {
+  public:
+    void operator++();
+    Element operator*();
+    bool operator!=(const Iterator &);
+    WeirdCopyCtorType c;
+  };
+  const Iterator &begin() const;
+  const Iterator &end() const;
+};
+
+void implicitVarFalsePositive() {
+  for (const Element &E : Container()) {
+  }
+}