Improve diagnosis of generic types in @abi

A same-type constraint in an enclosing `where` clause will eliminate a generic parameter’s ABI impact. Teach `ABIDeclChecker::checkType()` about this so it can handle a known-unsupported case for `Swift.Result.init(catching:)`.

Author: beccadax

lib/Sema/TypeCheckAttrABI.cpp

@@ -222,6 +222,13 @@ SourceLoc getTypeLoc(AbstractStorageDecl *storage, Decl *owner = nullptr) {
   return loc;
 }
 
+/// Get a decl's generic signature, if it has one.
+GenericSignature getGenericSignature(Decl *decl) {
+  if (auto genericCtx = decl->getAsGenericContext())
+    return genericCtx->getGenericSignature();
+  return GenericSignature();
+}
+
 class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
   ASTContext &ctx;
   Decl *diagnoseOnDecl;
@@ -371,6 +378,8 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
 
     didDiagnose |= checkType(apiNorm.getPlainType(), abiNorm.getPlainType(),
                              apiTypeLoc, abiTypeLoc,
+                             getGenericSignature(apiDecl),
+                             getGenericSignature(abiDecl),
                              TypeOrigin::forParameter(abi));
 
     didDiagnose |= checkParameterFlags(apiNorm.getParameterFlags(),
@@ -471,6 +480,8 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
 
       didDiagnose |= checkType(apiThrowType, abiThrowType,
                                api.throwsLoc, abi.throwsLoc,
+                               getGenericSignature(apiDecl),
+                               getGenericSignature(abiDecl),
                                TypeOrigin::forThrowsEffect());
     }
 
@@ -621,10 +632,9 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
   bool visitDecl(Decl *api, Decl *abi) {
     bool didDiagnose = checkAttrs(api->getAttrs(), abi->getAttrs(), api, abi);
 
-    if (auto apiGenericCtx = api->getAsGenericContext()) {
-      auto abiGenericCtx = abi->getAsGenericContext();
-      didDiagnose |= checkGenericSignature(apiGenericCtx->getGenericSignature(),
-                                           abiGenericCtx->getGenericSignature(),
+    if (api->getAsGenericContext()) {
+      didDiagnose |= checkGenericSignature(getGenericSignature(api),
+                                           getGenericSignature(abi),
                                            api, abi);
     }
 
@@ -706,6 +716,7 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
                      abi->getResultInterfaceType(),
                      api->getResultTypeSourceRange().Start,
                      abi->getResultTypeSourceRange().Start,
+                     getGenericSignature(api), getGenericSignature(abi),
                      TypeOrigin::forResult());
   }
 
@@ -723,6 +734,7 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
 
     if (checkType(api->getValueInterfaceType(), abi->getValueInterfaceType(),
                   getTypeLoc(api), getTypeLoc(abi),
+                  getGenericSignature(api), getGenericSignature(abi),
                   TypeOrigin::forUnspecified()))
       return true;
 
@@ -934,10 +946,11 @@ class ABIDeclChecker : public ASTComparisonVisitor<ABIDeclChecker> {
   // MARK: @abi checking - types
 
   bool checkType(Type api, Type abi, SourceLoc apiLoc, SourceLoc abiLoc,
+                 GenericSignature apiSig, GenericSignature abiSig,
                  TypeOrigin origin) {
     if (!api.isNull() && !abi.isNull()) {
-      Type apiNorm = normalizeType(api);
-      Type abiNorm = normalizeType(abi);
+      Type apiNorm = normalizeType(api->getReducedType(apiSig));
+      Type abiNorm = normalizeType(abi->getReducedType(abiSig));
       if (apiNorm->isEqual(abiNorm)) {
         return false;
       }

test/attr/attr_abi.swift

@@ -220,6 +220,40 @@ var throws00Var: Int { get { fatalError() } }
 @abi(var throws11Var: Int)
 var throws11Var: Int { get throws { fatalError() } }
 
+enum ErsatzResult<Success, Failure: Error> {}
+
+extension ErsatzResult where Failure == Swift.Error {
+  // The `where` clause makes `throws(Failure)` equivalent to `throws`.
+
+  // Similar to Swift.Result.init(__untyped_throws_catching:)
+  @abi(
+    init(
+      catching body: () throws -> Success
+    )
+  )
+  init(
+    __untyped_throws_catching body: () throws(Failure) -> Success
+  ) {}
+
+  @abi(func get() throws -> Success)
+  func __untyped_throws_get() throws(Failure) -> Success { fatalError() }
+}
+
+extension ErsatzResult {
+  // Should not be allowed, as `Failure` is still generic
+  @abi(
+    init(
+      unconstrainedCatching body: () throws -> Success // expected-error {{parameter 'body' type '() throws -> Success' in '@abi' should match '() throws(Failure) -> Success'}}
+    )
+  )
+  init(
+    __untyped_throws_catching_bad body: () throws(Failure) -> Success // expected-note {{should match type here}}
+  ) {}
+
+  @abi(func unconstrainedGet() throws -> Success) // expected-error @:32 {{thrown type 'any Error' in '@abi' should match 'Failure'}}
+  func __untyped_throws_get_bad() throws(Failure) -> Success { fatalError() } // expected-note {{should match type here}}
+}
+
 //
 // Async effect checking
 //
@@ -999,20 +1033,6 @@ func testNormalProtocolsGeneric<A: CustomStringConvertible, B>( // expected-note
   _: A, _: B
 ) {}
 
-enum ErsatzResult<Success, Failure: Error> {}
-extension ErsatzResult where Failure == Swift.Error {
-  // Similar to Swift.Result.init(__untyped_throws_catching:)
-  // FIXME: The where clause makes this ABI-compatible, but we can't tell that.
-  @abi(
-    init(
-      catching body: () throws -> Success // expected-error {{parameter 'body' type '() throws -> Success' in '@abi' should match '() throws(Failure) -> Success'}}
-    )
-  )
-  init(
-    __untyped_throws_catching body: () throws(Failure) -> Success // expected-note {{should match type here}}
-  ) {}
-}
-
 //
 // Static/Instance and interactions with `final`
 //