[Parse] [SR-5674] Add fix-it for computed 'let' declaration

include/swift/Parse/Parser.h

@@ -836,7 +836,8 @@ class Parser {
                        SourceLoc staticLoc, ParsedAccessors &accessors);
   void parseAccessorBodyDelayed(AbstractFunctionDecl *AFD);
   VarDecl *parseDeclVarGetSet(Pattern *pattern, ParseDeclOptions Flags,
-                              SourceLoc StaticLoc, bool hasInitializer,
+                              SourceLoc StaticLoc, SourceLoc VarLoc,
+                              bool hasInitializer,
                               const DeclAttributes &Attributes,
                               SmallVectorImpl<Decl *> &Decls);
 

lib/Parse/ParseDecl.cpp

@@ -4035,7 +4035,8 @@ void Parser::parseAccessorBodyDelayed(AbstractFunctionDecl *AFD) {
 /// \brief Parse the brace-enclosed getter and setter for a variable.
 VarDecl *Parser::parseDeclVarGetSet(Pattern *pattern,
                                     ParseDeclOptions Flags,
-                                    SourceLoc StaticLoc, bool hasInitializer,
+                                    SourceLoc StaticLoc, SourceLoc VarLoc,
+                                    bool hasInitializer,
                                     const DeclAttributes &Attributes,
                                     SmallVectorImpl<Decl *> &Decls) {
   bool Invalid = false;
@@ -4090,12 +4091,15 @@ VarDecl *Parser::parseDeclVarGetSet(Pattern *pattern,
 
   // Reject accessors on 'let's after parsing them (for better recovery).
   if (PrimaryVar->isLet() && !Attributes.hasAttribute<SILStoredAttr>()) {
+    Diag<> DiagID;
     if (accessors.WillSet || accessors.DidSet)
-      diagnose(accessors.LBLoc, diag::let_cannot_be_observing_property);
+      DiagID = diag::let_cannot_be_observing_property;
     else if (accessors.Addressor || accessors.MutableAddressor)
-      diagnose(accessors.LBLoc, diag::let_cannot_be_addressed_property);
+      DiagID = diag::let_cannot_be_addressed_property;
     else
-      diagnose(accessors.LBLoc, diag::let_cannot_be_computed_property);
+      DiagID = diag::let_cannot_be_computed_property;
+
+    diagnose(accessors.LBLoc, DiagID).fixItReplace(VarLoc, "var");
     PrimaryVar->setSpecifier(VarDecl::Specifier::Var);
     Invalid = true;
   }
@@ -4598,7 +4602,8 @@ Parser::parseDeclVar(ParseDeclOptions Flags,
     } else if (Tok.is(tok::l_brace)) {
       HasAccessors = true;
 
-      if (auto *boundVar = parseDeclVarGetSet(pattern, Flags, StaticLoc,
+      if (auto *boundVar = parseDeclVarGetSet(pattern, Flags,
+                                              StaticLoc, VarLoc,
                                               PatternInit != nullptr,
                                               Attributes, Decls)) {
         if (PatternInit && !boundVar->hasStorage()) {

test/Sema/immutability.swift

@@ -2,12 +2,12 @@
 
 func markUsed<T>(_ t: T) {}
 
-let bad_property_1: Int {    // expected-error {{'let' declarations cannot be computed properties}}
+let bad_property_1: Int {    // expected-error {{'let' declarations cannot be computed properties}} {{1-4=var}}
   get {
     return 42
   }
 }
-let bad_property_2: Int = 0 { // expected-error {{'let' declarations cannot be computed properties}} expected-error {{variable with getter/setter cannot have an initial value}}
+let bad_property_2: Int = 0 { // expected-error {{'let' declarations cannot be computed properties}} {{1-4=var}} expected-error {{variable with getter/setter cannot have an initial value}}
   get {
     return 42
   }

test/decl/protocol/protocols.swift

@@ -448,7 +448,7 @@ struct X4 : P1 { // expected-error{{type 'X4' does not conform to protocol 'P1'}
 
 protocol ShouldntCrash {
   // rdar://16109996
-  let fullName: String { get }  // expected-error {{'let' declarations cannot be computed properties}}
+  let fullName: String { get }  // expected-error {{'let' declarations cannot be computed properties}} {{3-6=var}}
 
   // <rdar://problem/17200672> Let in protocol causes unclear errors and crashes
   let fullName2: String  // expected-error {{immutable property requirement must be declared as 'var' with a '{ get }' specifier}}

test/decl/var/properties.swift

@@ -1027,7 +1027,7 @@ struct PropertiesWithOwnershipTypes {
 
 // <rdar://problem/16608609> Assert (and incorrect error message) when defining a constant stored property with observers
 class Test16608609 {
-   let constantStored: Int = 0 {  // expected-error {{'let' declarations cannot be observing properties}}
+   let constantStored: Int = 0 {  // expected-error {{'let' declarations cannot be observing properties}} {{4-7=var}}
       willSet {
       }
       didSet {

test/decl/var/static_var.swift

@@ -259,7 +259,7 @@ extension ProtoAdopter : ProtosEvilTwin {}
 public struct Foo { // expected-note {{to match this opening '{'}}}
   public static let S { a // expected-error{{computed property must have an explicit type}} {{22-22=: <# Type #>}}
     // expected-error@-1{{type annotation missing in pattern}}
-    // expected-error@-2{{'let' declarations cannot be computed properties}}
+    // expected-error@-2{{'let' declarations cannot be computed properties}} {{17-20=var}}
     // expected-error@-3{{use of unresolved identifier 'a'}}
 }