Merge pull request #38662 from RAJAGOPALAN-GANGADHARAN/sr_14951

Fixes SR-14951 : Print message of @available attribute within Protocol

Author: ahoppen

include/swift/AST/DiagnosticsSema.def

@@ -2317,8 +2317,8 @@ NOTE(declared_protocol_conformance_here,none,
      (Type, unsigned, Identifier, Identifier))
 
 ERROR(witness_unavailable,none,
-        "unavailable %0 %1 was used to satisfy a requirement of protocol %2",
-        (DescriptiveDeclKind, DeclName, Identifier))
+        "unavailable %0 %1 was used to satisfy a requirement of protocol %2%select{|: %3}3",
+        (DescriptiveDeclKind, DeclName, Identifier, StringRef))
 
 ERROR(redundant_conformance,none,
       "redundant conformance of %0 to protocol %1", (Type, Identifier))

lib/Sema/TypeCheckProtocol.cpp

@@ -4198,11 +4198,12 @@ ConformanceChecker::resolveWitnessViaLookup(ValueDecl *requirement) {
                                     NormalProtocolConformance *conformance) {
           auto &diags = witness->getASTContext().Diags;
           SourceLoc diagLoc = getLocForDiagnosingWitness(conformance, witness);
-          diags.diagnose(diagLoc,
-                         diag::witness_unavailable,
-                         witness->getDescriptiveKind(),
-                         witness->getName(),
-                         conformance->getProtocol()->getName());
+          auto *attr = AvailableAttr::isUnavailable(witness);
+          EncodedDiagnosticMessage EncodedMessage(attr->Message);
+          diags.diagnose(diagLoc, diag::witness_unavailable,
+                         witness->getDescriptiveKind(), witness->getName(),
+                         conformance->getProtocol()->getName(),
+                         EncodedMessage.Message);
           emitDeclaredHereIfNeeded(diags, diagLoc, witness);
           diags.diagnose(requirement, diag::kind_declname_declared_here,
                          DescriptiveDeclKind::Requirement,

test/decl/protocol/req/unavailable.swift

@@ -40,3 +40,24 @@ struct ConformsToP2 {
 }
 extension ConformsToP2: P {} // expected-error{{type 'ConformsToP2' does not conform to protocol 'P'}}
 // expected-error@-1 {{unavailable instance method 'foo(bar:)' was used to satisfy a requirement of protocol 'P'}}
+
+
+// Include message string from @available attribute if provided
+protocol Unavail {
+  associatedtype T
+  func req() // expected-note {{requirement 'req()' declared here}}
+}
+extension Unavail {
+  func req() {}
+}
+extension Unavail where T == Self {
+  @available(*, unavailable, message: "write it yourself") func req() {} // expected-note {{'req()' declared here}}
+}
+
+struct NonSelfT: Unavail {
+  typealias T = Int
+}
+struct SelfT: Unavail { // expected-error {{type 'SelfT' does not conform to protocol 'Unavail'}}
+  // expected-error@-1 {{unavailable instance method 'req()' was used to satisfy a requirement of protocol 'Unavail': write it yourself}}
+  typealias T = SelfT
+}