ASTScope: Don't silently drop duplicate AST nodes

Instead, let's rely on the existing source range assertions.
They will fire if we add two nodes with overlapping or
equal source ranges.

Author: slavapestov

include/swift/AST/ASTScope.h

@@ -224,7 +224,6 @@ class ASTScopeImpl {
   virtual NullablePtr<DeclAttribute> getDeclAttributeIfAny() const {
     return nullptr;
   }
-  virtual NullablePtr<const void> getReferrent() const { return nullptr; }
 
 #pragma mark - debugging and printing
 
@@ -470,9 +469,6 @@ class Portion {
   virtual NullablePtr<const ASTScopeImpl>
   getLookupLimitFor(const GenericTypeOrExtensionScope *) const;
 
-  virtual const Decl *
-  getReferrentOfScope(const GenericTypeOrExtensionScope *s) const;
-
   virtual NullablePtr<ASTScopeImpl>
   insertionPointForDeferredExpansion(IterableTypeScope *) const = 0;
   };
@@ -493,9 +489,6 @@ class Portion {
     NullablePtr<const ASTScopeImpl>
     getLookupLimitFor(const GenericTypeOrExtensionScope *) const override;
 
-    const Decl *
-    getReferrentOfScope(const GenericTypeOrExtensionScope *s) const override;
-
     NullablePtr<ASTScopeImpl>
     insertionPointForDeferredExpansion(IterableTypeScope *) const override;
   };
@@ -570,7 +563,6 @@ class GenericTypeOrExtensionScope : public ASTScopeImpl {
 
   virtual Decl *getDecl() const = 0;
   NullablePtr<Decl> getDeclIfAny() const override { return getDecl(); }
-  NullablePtr<const void> getReferrent() const override;
 
 private:
   AnnotatedInsertionPoint
@@ -745,7 +737,6 @@ class GenericParamScope final : public ASTScopeImpl {
 
   /// Actually holder is always a GenericContext, need to test if
   /// ProtocolDecl or SubscriptDecl but will refactor later.
-  NullablePtr<const void> getReferrent() const override;
   std::string getClassName() const override;
   SourceRange
   getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
@@ -788,8 +779,6 @@ class AbstractFunctionDeclScope final : public ASTScopeImpl {
   virtual NullablePtr<Decl> getDeclIfAny() const override { return decl; }
   Decl *getDecl() const { return decl; }
 
-  NullablePtr<const void> getReferrent() const override;
-
 protected:
   NullablePtr<const GenericParamList> genericParams() const override;
 };
@@ -902,7 +891,6 @@ class AttachedPropertyWrapperScope final : public ASTScopeImpl {
   NullablePtr<DeclAttribute> getDeclAttributeIfAny() const override {
     return attr;
   }
-  NullablePtr<const void> getReferrent() const override;
 
 private:
   void expandAScopeThatDoesNotCreateANewInsertionPoint(ScopeCreator &);
@@ -970,8 +958,6 @@ class PatternEntryDeclScope final : public AbstractPatternEntryScope {
   SourceRange
   getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
 
-  NullablePtr<const void> getReferrent() const override;
-
 protected:
   bool lookupLocalsOrMembers(DeclConsumer) const override;
   bool isLabeledStmtLookupTerminator() const override;
@@ -1072,7 +1058,6 @@ class CaptureListScope final : public ASTScopeImpl {
   getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
   NullablePtr<Expr> getExprIfAny() const override { return expr; }
   Expr *getExpr() const { return expr; }
-  NullablePtr<const void> getReferrent() const override;
   bool lookupLocalsOrMembers(DeclConsumer) const override;
 };
 
@@ -1094,7 +1079,6 @@ class ClosureParametersScope final : public ASTScopeImpl {
   }
   NullablePtr<Expr> getExprIfAny() const override { return closureExpr; }
   Expr *getExpr() const { return closureExpr; }
-  NullablePtr<const void> getReferrent() const override;
 
 protected:
   ASTScopeImpl *expandSpecifically(ScopeCreator &scopeCreator) override;
@@ -1128,7 +1112,6 @@ class TopLevelCodeScope final : public ASTScopeImpl {
   getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
   virtual NullablePtr<Decl> getDeclIfAny() const override { return decl; }
   Decl *getDecl() const { return decl; }
-  NullablePtr<const void> getReferrent() const override;
 };
 
 /// The \c _@specialize attribute.
@@ -1153,7 +1136,6 @@ class SpecializeAttributeScope final : public ASTScopeImpl {
   NullablePtr<DeclAttribute> getDeclAttributeIfAny() const override {
     return specializeAttr;
   }
-  NullablePtr<const void> getReferrent() const override;
 
 protected:
   ASTScopeImpl *expandSpecifically(ScopeCreator &) override;
@@ -1183,7 +1165,6 @@ class DifferentiableAttributeScope final : public ASTScopeImpl {
   NullablePtr<DeclAttribute> getDeclAttributeIfAny() const override {
     return differentiableAttr;
   }
-  NullablePtr<const void> getReferrent() const override;
 
 protected:
   ASTScopeImpl *expandSpecifically(ScopeCreator &) override;
@@ -1214,7 +1195,6 @@ class SubscriptDeclScope final : public ASTScopeImpl {
 public:
   virtual NullablePtr<Decl> getDeclIfAny() const override { return decl; }
   Decl *getDecl() const { return decl; }
-  NullablePtr<const void> getReferrent() const override;
 
 protected:
   NullablePtr<const GenericParamList> genericParams() const override;
@@ -1244,7 +1224,6 @@ class AbstractStmtScope : public ASTScopeImpl {
   getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
   virtual Stmt *getStmt() const = 0;
   NullablePtr<Stmt> getStmtIfAny() const override { return getStmt(); }
-  NullablePtr<const void> getReferrent() const override;
 
 protected:
   bool isLabeledStmtLookupTerminator() const override;