Fixing /IDE/crashers/016-swift-mangle-mangler-mangleidentifier.swift (#6079)

Author: nkcsgexi

lib/AST/Mangle.cpp

@@ -1592,7 +1592,7 @@ void Mangler::mangleEntity(const ValueDecl *decl,
                            unsigned uncurryLevel) {
   assert(!isa<ConstructorDecl>(decl));
   assert(!isa<DestructorDecl>(decl));
-  
+
   // entity ::= static? entity-kind context entity-name
   if (decl->isStatic())
     Buffer << 'Z';
@@ -1605,7 +1605,12 @@ void Mangler::mangleEntity(const ValueDecl *decl,
       return mangleAccessorEntity(accessorKind, func->getAddressorKind(),
                                   func->getAccessorStorageDecl());
   }
-  
+
+  // Avoid mangling nameless entity. This may happen in erroneous code as code
+  // completion.
+  if (!decl->hasName())
+    return;
+
   if (isa<VarDecl>(decl)) {
     Buffer << 'v';
   } else if (isa<SubscriptDecl>(decl)) {

validation-test/IDE/crashers/016-swift-mangle-mangler-mangleidentifier.swift

@@ -0,0 +1,3 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+// REQUIRES: asserts
+var d{let:{func a#^A^#

validation-test/IDE/crashers/100-swift-mangle-mangler-mangledeclname.swift

@@ -0,0 +1,2 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+{let:{class S(}#^A^#