[Diagnostic] Fix diagnostic when checking conformance for IUO of gene… (swiftlang#32987)

* [Diagnostic] Fix diagnostic when checking conformance for IUO of generic parameter

Prints TypeRepr in diagnostic if possible to throw
accurate diagnostic for IUO conformance checking
Fixes [rdar://problem/64953106]. Fixes SR-13119

* Nested name lookup tests update

Name lookup will see the innermost name anyway and
preferred over fully qualified name. Hence the test
cases are also updated.

* Replaced a letter in test case that inadvertently got added

* Code format, corrections and better comments

This commit includes better comments for easy
understanding, formatted the bug fix code with
clang-format and fixes wrong variables inadvertently
introduced.

* [Test] Update type in struct codable test

This commit changes diagnostic type from error type
to Int. Although this diagnostic updated is incorrect, this will
be resolved when 32371 gets pulled.

Author: srinikhil-07

include/swift/AST/DiagnosticsSema.def

@@ -2795,7 +2795,7 @@ WARNING(differentiable_let_property_implicit_noderivative_fixit,none,
 NOTE(codable_extraneous_codingkey_case_here,none,
      "CodingKey case %0 does not match any stored properties", (Identifier))
 NOTE(codable_non_conforming_property_here,none,
-     "cannot automatically synthesize %0 because %1 does not conform to %0", (Type, Type))
+     "cannot automatically synthesize %0 because %1 does not conform to %0", (Type, TypeLoc))
 NOTE(codable_non_decoded_property_here,none,
      "cannot automatically synthesize %0 because %1 does not have a matching CodingKey and does not have a default value", (Type, Identifier))
 NOTE(codable_codingkeys_type_is_not_an_enum_here,none,

lib/Sema/DerivedConformanceCodable.cpp

@@ -172,10 +172,20 @@ static bool validateCodingKeysEnum(DerivedConformance &derived,
         properties.erase(it);
         break;
 
-      case DoesNotConform:
+      case DoesNotConform: {
+        // We use a TypeLoc here so diagnostics can show the type
+        // as written by the user in source if possible. This is useful
+        // when the user has written an IUO type for example, since
+        // diagnostics would show the type as 'T?' instead of 'T!' if
+        // we use a Type instead.
+        TypeLoc typeLoc = {
+            it->second->getTypeReprOrParentPatternTypeRepr(),
+            it->second->getType(),
+        };
         it->second->diagnose(diag::codable_non_conforming_property_here,
-                             derived.getProtocolType(), it->second->getType());
+                             derived.getProtocolType(), typeLoc);
         LLVM_FALLTHROUGH;
+      }
 
       case TypeNotValidated:
         // We don't produce a diagnostic for a type which failed to validate.
@@ -352,10 +362,20 @@ static EnumDecl *synthesizeCodingKeysEnum(DerivedConformance &derived) {
         break;
       }
 
-      case DoesNotConform:
+      case DoesNotConform: {
+        // We use a TypeLoc here so diagnostics can show the type
+        // as written by the user in source if possible. This is useful
+        // when the user has written an IUO type for example, since
+        // diagnostics would show the type as 'T?' instead of 'T!' if
+        // we use a Type instead.
+        TypeLoc typeLoc = {
+            varDecl->getTypeReprOrParentPatternTypeRepr(),
+            varDecl->getType(),
+        };
         varDecl->diagnose(diag::codable_non_conforming_property_here,
-                          derived.getProtocolType(), varDecl->getType());
+                          derived.getProtocolType(), typeLoc);
         LLVM_FALLTHROUGH;
+      }
 
       case TypeNotValidated:
         // We don't produce a diagnostic for a type which failed to validate.

test/decl/protocol/special/coding/class_codable_excluded_optional_properties.swift

@@ -45,8 +45,8 @@ class ClassWithNonExcludedVarMembers : Codable { // expected-error {{type 'Class
     // AnyHashable does not conform to Codable.
     var p3: AnyHashable? // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
     // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
-    var p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
-    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
+    var p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable!' does not conform to 'Decodable'}}
+    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable!' does not conform to 'Encodable'}}
 }
 
 class ClassWithExcludedVarMembers : Codable {

test/decl/protocol/special/coding/class_codable_failure_diagnostics.swift

@@ -9,8 +9,8 @@ class C1 : Codable {
   var a: String = ""
   var b: Int = 0
   var c: Nested = Nested()
-  // expected-note@-1 {{cannot automatically synthesize 'Decodable' because 'C1.Nested' does not conform to 'Decodable'}}
-  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because 'C1.Nested' does not conform to 'Encodable'}}
+  // expected-note@-1 {{cannot automatically synthesize 'Decodable' because 'Nested' does not conform to 'Decodable'}}
+  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because 'Nested' does not conform to 'Encodable'}}
 }
 
 // Codable class with non-enum CodingKeys.

test/decl/protocol/special/coding/struct_codable_excluded_optional_properties.swift

@@ -12,8 +12,8 @@ struct StructWithNonExcludedLetMembers : Codable { // expected-error {{type 'Str
     // AnyHashable does not conform to Codable.
     let p3: AnyHashable? // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
     // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
-    let p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
-    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
+    let p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable!' does not conform to 'Decodable'}}
+    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable!' does not conform to 'Encodable'}}
 }
 
 struct StructWithExcludedLetMembers : Codable { // expected-error {{type 'StructWithExcludedLetMembers' does not conform to protocol 'Decodable'}}
@@ -46,8 +46,8 @@ struct StructWithNonExcludedVarMembers : Codable { // expected-error {{type 'Str
     // AnyHashable does not conform to Codable.
     var p3: AnyHashable? // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
     // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
-    var p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable?' does not conform to 'Decodable'}}
-    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable?' does not conform to 'Encodable'}}
+    var p4: AnyHashable! // expected-note {{cannot automatically synthesize 'Decodable' because 'AnyHashable!' does not conform to 'Decodable'}}
+    // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'AnyHashable!' does not conform to 'Encodable'}}
 }
 
 struct StructWithExcludedVarMembers : Codable {

test/decl/protocol/special/coding/struct_codable_failure_diagnostics.swift

@@ -9,8 +9,8 @@ struct S1 : Codable {
   var a: String = ""
   var b: Int = 0
   var c: Nested = Nested()
-  // expected-note@-1 {{cannot automatically synthesize 'Decodable' because 'S1.Nested' does not conform to 'Decodable'}}
-  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because 'S1.Nested' does not conform to 'Encodable'}}
+  // expected-note@-1 {{cannot automatically synthesize 'Decodable' because 'Nested' does not conform to 'Decodable'}}
+  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because 'Nested' does not conform to 'Encodable'}}
 }
 
 // Codable struct with non-enum CodingKeys.

test/decl/protocol/special/coding/struct_codable_simple.swift

@@ -34,8 +34,8 @@ let _ = SimpleStruct.CodingKeys.self // expected-error {{'CodingKeys' is inacces
 struct SR_12248_1: Codable { // expected-error {{type 'SR_12248_1' does not conform to protocol 'Encodable'}}
   var x: Int // expected-note {{'x' previously declared here}}
   var x: Int // expected-error {{invalid redeclaration of 'x'}}
-  // expected-note@-1 {{cannot automatically synthesize 'Encodable' because '<<error type>>' does not conform to 'Encodable'}}
-  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because '<<error type>>' does not conform to 'Encodable'}}
+  // expected-note@-1 {{cannot automatically synthesize 'Encodable' because 'Int' does not conform to 'Encodable'}}
+  // expected-note@-2 {{cannot automatically synthesize 'Encodable' because 'Int' does not conform to 'Encodable'}}
 }
 
 struct SR_12248_2: Decodable {