[clang-tidy] fix a crash with -fdelayed-template-parsing in UnnecessaryValueParamCheck.

Summary:
This is the same kind of bug than [[ http://reviews.llvm.org/D18238 | D18238 ]].

Fix crashes caused by deferencing null pointer when declarations parsing may be delayed.
The body of the declarations may be null.

The crashes were observed with a Windows build of clang-tidy and the following command-line.
```
command-line switches: -fms-compatibility-version=19 -fms-compatibility
```

Reviewers: alexfh

Subscribers: kimgr, LegalizeAdulthood, cfe-commits

Differential Revision: http://reviews.llvm.org/D18852

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@265681 91177308-0d34-0410-b5e6-96231b3b80d8

clang-tidy/performance/UnnecessaryValueParamCheck.cpp

@@ -51,6 +51,10 @@ void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
   bool IsConstQualified =
       Param->getType().getCanonicalType().isConstQualified();
 
+  // Skip declarations delayed by late template parsing without a body.
+  if (!Function->getBody())
+    return;
+
   // Do not trigger on non-const value parameters when:
   // 1. they are in a constructor definition since they can likely trigger
   //    misc-move-constructor-init which will suggest to move the argument.

test/clang-tidy/performance-unnecessary-value-param-delayed.cpp

@@ -0,0 +1,171 @@
+// RUN: %check_clang_tidy %s performance-unnecessary-value-param %t -- -- -fdelayed-template-parsing
+
+struct ExpensiveToCopyType {
+  const ExpensiveToCopyType & constReference() const {
+    return *this;
+  }
+  void nonConstMethod();
+  virtual ~ExpensiveToCopyType();
+};
+
+void mutate(ExpensiveToCopyType &);
+void mutate(ExpensiveToCopyType *);
+void useAsConstReference(const ExpensiveToCopyType &);
+void useByValue(ExpensiveToCopyType);
+
+// This class simulates std::pair<>. It is trivially copy constructible
+// and trivially destructible, but not trivially copy assignable.
+class SomewhatTrivial {
+ public:
+  SomewhatTrivial();
+  SomewhatTrivial(const SomewhatTrivial&) = default;
+  ~SomewhatTrivial() = default;
+  SomewhatTrivial& operator=(const SomewhatTrivial&);
+};
+
+void positiveExpensiveConstValue(const ExpensiveToCopyType Obj);
+// CHECK-FIXES: void positiveExpensiveConstValue(const ExpensiveToCopyType& Obj);
+void positiveExpensiveConstValue(const ExpensiveToCopyType Obj) {
+  // CHECK-MESSAGES: [[@LINE-1]]:60: warning: the const qualified parameter 'Obj' is copied for each invocation; consider making it a reference [performance-unnecessary-value-param]
+  // CHECK-FIXES: void positiveExpensiveConstValue(const ExpensiveToCopyType& Obj) {
+}
+
+void positiveExpensiveValue(ExpensiveToCopyType Obj);
+// CHECK-FIXES: void positiveExpensiveValue(const ExpensiveToCopyType& Obj);
+void positiveExpensiveValue(ExpensiveToCopyType Obj) {
+  // CHECK-MESSAGES: [[@LINE-1]]:49: warning: the parameter 'Obj' is copied for each invocation but only used as a const reference; consider making it a const reference [performance-unnecessary-value-param]
+  // CHECK-FIXES: void positiveExpensiveValue(const ExpensiveToCopyType& Obj) {
+  Obj.constReference();
+  useAsConstReference(Obj);
+  auto Copy = Obj;
+  useByValue(Obj);
+}
+
+void positiveWithComment(const ExpensiveToCopyType /* important */ S);
+// CHECK-FIXES: void positiveWithComment(const ExpensiveToCopyType& /* important */ S);
+void positiveWithComment(const ExpensiveToCopyType /* important */ S) {
+  // CHECK-MESSAGES: [[@LINE-1]]:68: warning: the const qualified
+  // CHECK-FIXES: void positiveWithComment(const ExpensiveToCopyType& /* important */ S) {
+}
+
+void positiveUnnamedParam(const ExpensiveToCopyType) {
+  // CHECK-MESSAGES: [[@LINE-1]]:52: warning: the const qualified parameter #1
+  // CHECK-FIXES: void positiveUnnamedParam(const ExpensiveToCopyType&) {
+}
+
+void positiveAndNegative(const ExpensiveToCopyType ConstCopy, const ExpensiveToCopyType& ConstRef, ExpensiveToCopyType Copy);
+// CHECK-FIXES: void positiveAndNegative(const ExpensiveToCopyType& ConstCopy, const ExpensiveToCopyType& ConstRef, const ExpensiveToCopyType& Copy);
+void positiveAndNegative(const ExpensiveToCopyType ConstCopy, const ExpensiveToCopyType& ConstRef, ExpensiveToCopyType Copy) {
+  // CHECK-MESSAGES: [[@LINE-1]]:52: warning: the const qualified parameter 'ConstCopy'
+  // CHECK-MESSAGES: [[@LINE-2]]:120: warning: the parameter 'Copy'
+  // CHECK-FIXES: void positiveAndNegative(const ExpensiveToCopyType& ConstCopy, const ExpensiveToCopyType& ConstRef, const ExpensiveToCopyType& Copy) {
+}
+
+struct PositiveConstValueConstructor {
+  PositiveConstValueConstructor(const ExpensiveToCopyType ConstCopy) {}
+  // CHECK-MESSAGES: [[@LINE-1]]:59: warning: the const qualified parameter 'ConstCopy'
+};
+
+template <typename T> void templateWithNonTemplatizedParameter(const ExpensiveToCopyType S, T V) {
+  // CHECK-MESSAGES: [[@LINE-1]]:90: warning: the const qualified parameter 'S'
+  // CHECK-FIXES: template <typename T> void templateWithNonTemplatizedParameter(const ExpensiveToCopyType& S, T V) {
+}
+
+void instantiated() {
+  templateWithNonTemplatizedParameter(ExpensiveToCopyType(), ExpensiveToCopyType());
+  templateWithNonTemplatizedParameter(ExpensiveToCopyType(), 5);
+}
+
+template <typename T> void negativeTemplateType(const T V) {
+}
+
+void negativeArray(const ExpensiveToCopyType[]) {
+}
+
+void negativePointer(ExpensiveToCopyType* Obj) {
+}
+
+void negativeConstPointer(const ExpensiveToCopyType* Obj) {
+}
+
+void negativeConstReference(const ExpensiveToCopyType& Obj) {
+}
+
+void negativeReference(ExpensiveToCopyType& Obj) {
+}
+
+void negativeUniversalReference(ExpensiveToCopyType&& Obj) {
+}
+
+void negativeSomewhatTrivialConstValue(const SomewhatTrivial Somewhat) {
+}
+
+void negativeSomewhatTrivialValue(SomewhatTrivial Somewhat) {
+}
+
+void negativeConstBuiltIn(const int I) {
+}
+
+void negativeValueBuiltIn(int I) {
+}
+
+void negativeValueIsMutatedByReference(ExpensiveToCopyType Obj) {
+  mutate(Obj);
+}
+
+void negativeValueIsMutatatedByPointer(ExpensiveToCopyType Obj) {
+  mutate(&Obj);
+}
+
+void negativeValueIsReassigned(ExpensiveToCopyType Obj) {
+  Obj = ExpensiveToCopyType();
+}
+
+void negativeValueNonConstMethodIsCalled(ExpensiveToCopyType Obj) {
+  Obj.nonConstMethod();
+}
+
+struct NegativeValueCopyConstructor {
+  NegativeValueCopyConstructor(ExpensiveToCopyType Copy) {}
+};
+
+template <typename T>
+struct Container {
+  typedef const T & const_reference;
+};
+
+void NegativeTypedefParam(const Container<ExpensiveToCopyType>::const_reference Param) {
+}
+
+#define UNNECESSARY_VALUE_PARAM_IN_MACRO_BODY()         \
+  void inMacro(const ExpensiveToCopyType T) {           \
+  }                                                     \
+// Ensure fix is not applied.
+// CHECK-FIXES: void inMacro(const ExpensiveToCopyType T) {
+
+UNNECESSARY_VALUE_PARAM_IN_MACRO_BODY()
+// CHECK-MESSAGES: [[@LINE-1]]:1: warning: the const qualified parameter 'T'
+
+#define UNNECESSARY_VALUE_PARAM_IN_MACRO_ARGUMENT(ARGUMENT)     \
+  ARGUMENT
+
+UNNECESSARY_VALUE_PARAM_IN_MACRO_ARGUMENT(void inMacroArgument(const ExpensiveToCopyType InMacroArg) {})
+// CHECK-MESSAGES: [[@LINE-1]]:90: warning: the const qualified parameter 'InMacroArg'
+// CHECK-FIXES: void inMacroArgument(const ExpensiveToCopyType InMacroArg) {}
+
+struct VirtualMethod {
+  virtual ~VirtualMethod() {}
+  virtual void handle(ExpensiveToCopyType T) const = 0;
+};
+
+struct NegativeOverriddenMethod : public VirtualMethod {
+  void handle(ExpensiveToCopyType Overridden) const {
+    // CHECK-FIXES: handle(ExpensiveToCopyType Overridden) const {
+  }
+};
+
+struct NegativeDeletedMethod {
+  ~NegativeDeletedMethod() {}
+  NegativeDeletedMethod& operator=(NegativeDeletedMethod N) = delete;
+  // CHECK-FIXES: NegativeDeletedMethod& operator=(NegativeDeletedMethod N) = delete;
+};