[c++ interop] Swift should allow multiple SWIFT_CONFORMS_TO_PROTOCOL attributes on a C++ class.

include/swift/AST/DiagnosticsClangImporter.def

@@ -294,6 +294,9 @@ ERROR(both_returns_retained_returns_unretained, none,
       "SWIFT_RETURNS_UNRETAINED",
       (const clang::NamedDecl *))
 
+ERROR(redundant_conformance_protocol,none,
+     "redundant conformance of %0 to protocol '%1'", (Type, StringRef))
+
 ERROR(returns_retained_or_returns_unretained_for_non_cxx_frt_values, none,
       "%0 cannot be annotated with either SWIFT_RETURNS_RETAINED or "
       "SWIFT_RETURNS_UNRETAINED because it is not returning "

lib/ClangImporter/ImportDecl.cpp

@@ -69,6 +69,7 @@
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallBitVector.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
@@ -3105,6 +3106,8 @@ namespace {
       return result;
     }
 
+    using ProtocolSet = llvm::SmallSet<ProtocolDecl *, 4>;
+
     void
     addExplicitProtocolConformances(NominalTypeDecl *decl,
                                     const clang::CXXRecordDecl *clangDecl) {
@@ -3119,25 +3122,26 @@ namespace {
       if (!clangDecl->hasAttrs())
         return;
 
-      SmallVector<ValueDecl *, 1> results;
-      auto conformsToAttr =
-          llvm::find_if(clangDecl->getAttrs(), [](auto *attr) {
-            if (auto swiftAttr = dyn_cast<clang::SwiftAttrAttr>(attr))
-              return swiftAttr->getAttribute().starts_with("conforms_to:");
-            return false;
-          });
-      if (conformsToAttr == clangDecl->getAttrs().end())
-        return;
+      ProtocolSet alreadyAdded;
+      llvm::for_each(clangDecl->getAttrs(), [&](auto *attr) {
+        if (auto swiftAttr = dyn_cast<clang::SwiftAttrAttr>(attr)) {
+          if (swiftAttr->getAttribute().starts_with("conforms_to:"))
+            addExplicitProtocolConformance(decl, swiftAttr, alreadyAdded);
+        }
+      });
+    }
 
-      auto conformsToValue = cast<clang::SwiftAttrAttr>(*conformsToAttr)
-                                 ->getAttribute()
+    void addExplicitProtocolConformance(NominalTypeDecl *decl,
+                                        clang::SwiftAttrAttr *conformsToAttr,
+                                        ProtocolSet &alreadyAdded) {
+      auto conformsToValue = conformsToAttr->getAttribute()
                                  .drop_front(StringRef("conforms_to:").size())
                                  .str();
       auto names = StringRef(conformsToValue).split('.');
       auto moduleName = names.first;
       auto protocolName = names.second;
       if (protocolName.empty()) {
-        HeaderLoc attrLoc((*conformsToAttr)->getLocation());
+        HeaderLoc attrLoc(conformsToAttr->getLocation());
         Impl.diagnose(attrLoc, diag::conforms_to_missing_dot, conformsToValue);
         return;
       }
@@ -3145,20 +3149,24 @@ namespace {
       auto *mod = Impl.SwiftContext.getModuleByIdentifier(
           Impl.SwiftContext.getIdentifier(moduleName));
       if (!mod) {
-        HeaderLoc attrLoc((*conformsToAttr)->getLocation());
+        HeaderLoc attrLoc(conformsToAttr->getLocation());
         Impl.diagnose(attrLoc, diag::cannot_find_conforms_to_module,
                       conformsToValue, moduleName);
         return;
       }
+
+      SmallVector<ValueDecl *, 1> results;
       mod->lookupValue(Impl.SwiftContext.getIdentifier(protocolName),
                        NLKind::UnqualifiedLookup, results);
       if (results.empty()) {
-        HeaderLoc attrLoc((*conformsToAttr)->getLocation());
+        HeaderLoc attrLoc(conformsToAttr->getLocation());
         Impl.diagnose(attrLoc, diag::cannot_find_conforms_to, protocolName,
                       moduleName);
         return;
-      } else if (results.size() != 1) {
-        HeaderLoc attrLoc((*conformsToAttr)->getLocation());
+      }
+
+      if (results.size() != 1) {
+        HeaderLoc attrLoc(conformsToAttr->getLocation());
         Impl.diagnose(attrLoc, diag::conforms_to_ambiguous, protocolName,
                       moduleName);
         return;
@@ -3166,10 +3174,17 @@ namespace {
 
       auto result = results.front();
       if (auto protocol = dyn_cast<ProtocolDecl>(result)) {
+        auto [_, inserted] = alreadyAdded.insert(protocol);
+        if (!inserted) {
+          HeaderLoc attrLoc(conformsToAttr->getLocation());
+          Impl.diagnose(attrLoc, diag::redundant_conformance_protocol,
+                        decl->getDeclaredInterfaceType(), conformsToValue);
+        }
+
         decl->getAttrs().add(
             new (Impl.SwiftContext) SynthesizedProtocolAttr(protocol, &Impl, false));
       } else {
-        HeaderLoc attrLoc((*conformsToAttr)->getLocation());
+        HeaderLoc attrLoc((conformsToAttr)->getLocation());
         Impl.diagnose(attrLoc, diag::conforms_to_not_protocol, result,
                       conformsToValue);
       }

test/Interop/Cxx/class/Inputs/conforms-to.h

@@ -16,6 +16,13 @@ struct
   void play() const;
 };
 
+struct __attribute__((swift_attr("conforms_to:SwiftTest.Testable")))
+__attribute__((swift_attr(
+    "conforms_to:SwiftTest.Playable"))) MultipleConformanceHasTestAndPlay {
+  void test() const;
+  void play() const;
+};
+
 struct
     __attribute__((swift_attr("conforms_to:ImportedModule.ProtocolFromImportedModule")))
     HasImportedConf {
@@ -24,6 +31,8 @@ struct
 
 struct DerivedFromHasTest : HasTest {};
 struct DerivedFromDerivedFromHasTest : HasTest {};
+struct DerivedFromMultipleConformanceHasTestAndPlay
+    : MultipleConformanceHasTestAndPlay {};
 
 struct __attribute__((swift_attr("conforms_to:SwiftTest.Testable")))
 DerivedFromDerivedFromHasTestWithDuplicateArg : HasTest {};

test/Interop/Cxx/class/conforms-to-errors.swift

@@ -16,6 +16,65 @@ struct  __attribute__((swift_attr("conforms_to:SwiftTest.X"))) CX {};
 struct  __attribute__((swift_attr("conforms_to:SwiftTest.A"))) CA {};
 struct  __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CB {};
 
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:X"))) CXX {};
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:Mod.X"))) CXModX {};
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.X"))) CXTextX {};
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.A"))) CXA {};
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CXB {};
+struct  __attribute__((swift_attr("conforms_to:X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CXC {};
+
+
+struct  __attribute__((swift_attr("conforms_to:Mod.X")))
+    __attribute__((swift_attr("conforms_to:Mod.X"))) CModXModX {};
+struct  __attribute__((swift_attr("conforms_to:Mod.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.X"))) CModXTestX {};
+struct  __attribute__((swift_attr("conforms_to:Mod.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.A"))) CModXA {};
+struct  __attribute__((swift_attr("conforms_to:Mod.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CModXB {};
+struct  __attribute__((swift_attr("conforms_to:Mod.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CModXC {};
+
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.X"))) CTestXTextX {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.A"))) CTextXA {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CTextXB {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.X")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CTextXC {};
+
+
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.A")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.A"))) CAA {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.A")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CAB {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.A")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CAC {};
+
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.B")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.B"))) CBB {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.B")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CBC {};
+
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.C")))
+    __attribute__((swift_attr("conforms_to:SwiftTest.C"))) CCC {};
+
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.D"))) CD {};
+struct  __attribute__((swift_attr("conforms_to:SwiftTest.D"))) CDD: CD {};
+
+struct __attribute__((swift_attr("conforms_to:SwiftTest.D"))) CD2 {};
+struct CCDCD2 : CD, CD2 {};
+
+struct __attribute__((swift_attr("conforms_to:SwiftTest.D"))) 
+    __attribute__((swift_attr("conforms_to:SwiftTest.E"))) CDE {};
+
 //--- test.swift
 
 import Test
@@ -25,10 +84,78 @@ struct B {}
 protocol A {}
 protocol A {}
 
+protocol C {}
+protocol D {}
+protocol E: D {}
+
 // CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
 // CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
 // CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
 // CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
 // CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
-
 func test(_ inv: CInv, _ invMod: CModInv, _ x: CX, _ a: CA, _ b: CB) {}
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+// CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
+
+// CHECK: error: expected module name and protocol name separated by '.' in protocol conformance; 'X' is invalid
+func test(_ xx: CXX, _ xModx: CXModX, _ xTextX: CXTextX, _ cxa: CXA, _ cxb: CXB, _ cxc: CXC) {}
+
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+// CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
+
+// CHECK: module 'Mod' in specified protocol conformance 'Mod.X' is not found; did you mean to import it first?
+func test(_ modXModX: CModXModX, _ modXTestX: CModXTestX, _ modXA: CModXA, _ modXB: CModXB, _ modXC: CModXC) {}
+
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+// CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
+
+// CHECK: error: protocol 'X' in specified protocol conformance is not found in module 'SwiftTest'
+func test(_ testXTextX: CTestXTextX, _ textXA: CTextXA, _ textXB: CTextXB, _ textXC: CTextXC) {}
+
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+// CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
+
+// CHECK: error: ambiguous reference to protocol 'A' in specified protocol conformance; module 'SwiftTest' contains multiple protocols named 'A'
+func test(_ aa: CAA, _ ab: CAB, _ ac: CAC) {}
+
+// CHECK: error: struct 'B' referenced in protocol conformance 'SwiftTest.B' is not a protocol
+func test(_ bb: CBB, _ bc: CBC) {}
+
+// CHECK: error: redundant conformance of 'CCC' to protocol 'SwiftTest.C'
+func test(_ cc: CCC) {}
+
+// CHECK-NOT: error: redundant conformance of 'CDD' to protocol 'SwiftTest.D'
+// CHECK-NOT: error: redundant conformance of 'CCDCD2' to protocol 'SwiftTest.D'
+// CHECK-NOT: error: redundant conformance of 'CDE' to protocol 'SwiftTest.D'
+func test(_ dd: CDD, _ dd2: CCDCD2, de: CDE) {}

test/Interop/Cxx/class/conforms-to.swift

@@ -35,13 +35,24 @@ func callee(_ _: Playable) {
 func caller(_ x: Playable) {
     callee(x)
 }
+
+func caller(_ x: MultipleConformanceHasTestAndPlay) {
+    callee(x as Testable)
+    callee(x as Playable)
+}
+
 func caller(_ x: DerivedFromHasPlay) { callee(x) }
 func caller(_ x: DerivedFromDerivedFromHasPlay) { callee(x) }
+func caller(_ x: DerivedFromMultipleConformanceHasTestAndPlay) {
+    callee(x as Testable)
+    callee(x as Playable)
+}
 
 func caller(_ x: HasTestAndPlay) {
     callee(x as Testable)
     callee(x as Playable)
 }
+
 func caller(_ x: DerivedFromHasTestAndPlay) {
     callee(x as Testable)
     callee(x as Playable)