[Serialization] Encode depth for cross-refs to generic parameters

include/swift/Serialization/ModuleFormat.h

@@ -52,7 +52,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 455; // Last change: reorder block IDs
+const uint16_t SWIFTMODULE_VERSION_MINOR = 456; // Last change: encode depth in generic param XREFs
 
 using DeclIDField = BCFixed<31>;
 
@@ -1403,7 +1403,8 @@ namespace decls_block {
 
   using XRefGenericParamPathPieceLayout = BCRecordLayout<
     XREF_GENERIC_PARAM_PATH_PIECE,
-    BCVBR<5> // index
+    BCVBR<5>, // depth
+    BCVBR<5>  // index
   >;
 
   using SILGenNameDeclAttrLayout = BCRecordLayout<

lib/Serialization/Deserialization.cpp

@@ -1622,8 +1622,8 @@ ModuleFile::resolveCrossReference(ModuleDecl *baseModule, uint32_t pathLen) {
                                            getXRefDeclNameForError());
       }
 
-      uint32_t paramIndex;
-      XRefGenericParamPathPieceLayout::readRecord(scratch, paramIndex);
+      uint32_t depth, paramIndex;
+      XRefGenericParamPathPieceLayout::readRecord(scratch, depth, paramIndex);
 
       pathTrace.addGenericParam(paramIndex);
 
@@ -1645,7 +1645,7 @@ ModuleFile::resolveCrossReference(ModuleDecl *baseModule, uint32_t pathLen) {
           assert(paramList && "Couldn't find constrained extension");
         } else {
           // Simple case: use the nominal type's generic parameters.
-          paramList = nominal->getGenericParams();
+          paramList = nominal->getGenericParamsOfContext();
         }
       } else if (auto alias = dyn_cast<TypeAliasDecl>(base)) {
         paramList = alias->getGenericParams();
@@ -1660,6 +1660,18 @@ ModuleFile::resolveCrossReference(ModuleDecl *baseModule, uint32_t pathLen) {
             "cross-reference to generic param for non-generic type",
             pathTrace, getXRefDeclNameForError());
       }
+
+      unsigned currentDepth = paramList->getDepth();
+      if (currentDepth < depth) {
+        return llvm::make_error<XRefError>(
+            "a containing type has been made non-generic",
+            pathTrace, getXRefDeclNameForError());
+      }
+      while (currentDepth > depth) {
+        paramList = paramList->getOuterParameters();
+        --currentDepth;
+      }
+
       if (paramIndex >= paramList->size()) {
         return llvm::make_error<XRefError>(
             "generic argument index out of bounds",

lib/Serialization/Serialization.cpp

@@ -2026,6 +2026,7 @@ void Serializer::writeCrossReference(const Decl *D) {
            "Cannot cross reference a generic type decl at module scope.");
     abbrCode = DeclTypeAbbrCodes[XRefGenericParamPathPieceLayout::Code];
     XRefGenericParamPathPieceLayout::emitRecord(Out, ScratchRecord, abbrCode,
+                                                genericParam->getDepth(),
                                                 genericParam->getIndex());
     return;
   }

test/Serialization/Inputs/xref-generic-params-other-extensions-constrained.swift

@@ -0,0 +1,28 @@
+public struct OuterNonGeneric {}
+extension OuterNonGeneric {
+  public struct InnerNonGeneric {}
+  public struct InnerGeneric<Y1, Y2> {}
+}
+
+public struct OuterGeneric<X1, X2> {}
+extension OuterGeneric {
+  public struct InnerNonGeneric {}
+  public struct InnerGeneric<Y1, Y2> {}
+}
+
+
+extension OuterNonGeneric.InnerNonGeneric {
+  public typealias AliasTy = ()
+}
+
+extension OuterNonGeneric.InnerGeneric where Y1: Equatable {
+  public typealias AliasTy = (Y1, Y2)
+}
+
+extension OuterGeneric.InnerNonGeneric where X1: Equatable {
+  public typealias AliasTy = (X1, X2)
+}
+
+extension OuterGeneric.InnerGeneric where X1: Equatable, Y1: Equatable {
+  public typealias AliasTy = (X1, X2, Y1, Y2)
+}

test/Serialization/Inputs/xref-generic-params-other-extensions-mixed.swift

@@ -0,0 +1,19 @@
+public struct OuterNonGeneric {}
+extension OuterNonGeneric {
+  public struct InnerNonGeneric {
+    public typealias AliasTy = ()
+  }
+  public struct InnerGeneric<Y1, Y2> {
+    public typealias AliasTy = (Y1, Y2)
+  }
+}
+
+public struct OuterGeneric<X1, X2> {}
+extension OuterGeneric {
+  public struct InnerNonGeneric {
+    public typealias AliasTy = (X1, X2)
+  }
+  public struct InnerGeneric<Y1, Y2> {
+    public typealias AliasTy = (X1, X2, Y1, Y2)
+  }
+}

test/Serialization/Inputs/xref-generic-params-other-extensions.swift

@@ -0,0 +1,28 @@
+public struct OuterNonGeneric {}
+extension OuterNonGeneric {
+  public struct InnerNonGeneric {}
+  public struct InnerGeneric<Y1, Y2> {}
+}
+
+public struct OuterGeneric<X1, X2> {}
+extension OuterGeneric {
+  public struct InnerNonGeneric {}
+  public struct InnerGeneric<Y1, Y2> {}
+}
+
+
+extension OuterNonGeneric.InnerNonGeneric {
+  public typealias AliasTy = ()
+}
+
+extension OuterNonGeneric.InnerGeneric {
+  public typealias AliasTy = (Y1, Y2)
+}
+
+extension OuterGeneric.InnerNonGeneric {
+  public typealias AliasTy = (X1, X2)
+}
+
+extension OuterGeneric.InnerGeneric {
+  public typealias AliasTy = (X1, X2, Y1, Y2)
+}

test/Serialization/Inputs/xref-generic-params-other.swift

@@ -0,0 +1,17 @@
+public struct OuterNonGeneric {
+  public struct InnerNonGeneric {
+    public typealias AliasTy = ()
+  }
+  public struct InnerGeneric<Y1, Y2> {
+    public typealias AliasTy = (Y1, Y2)
+  }
+}
+
+public struct OuterGeneric<X1, X2> {
+  public struct InnerNonGeneric {
+    public typealias AliasTy = (X1, X2)
+  }
+  public struct InnerGeneric<Y1, Y2> {
+    public typealias AliasTy = (X1, X2, Y1, Y2)
+  }
+}

test/Serialization/xref-generic-params.swift

@@ -0,0 +1,40 @@
+// RUN: %empty-directory(%t)
+
+// Run the same test several times, providing the nested types a different way
+// each time.
+
+// RUN: %target-swift-frontend -emit-module -o %t/a.swiftmodule -primary-file %s %S/Inputs/xref-generic-params-other.swift -module-name main
+// RUN: %target-swift-frontend -emit-module -o %t/b.swiftmodule %s -primary-file %S/Inputs/xref-generic-params-other.swift -module-name main
+// RUN: %target-swift-frontend -merge-modules -emit-module -o %t/main.swiftmodule %t/a.swiftmodule %t/b.swiftmodule -module-name main
+// RUN: %target-swift-ide-test -print-module -module-to-print=main -I %t -source-filename=x | %FileCheck %s
+
+// RUN: %target-swift-frontend -emit-module -o %t/a-extensions.swiftmodule -primary-file %s %S/Inputs/xref-generic-params-other-extensions.swift -module-name extensions
+// RUN: %target-swift-frontend -emit-module -o %t/b-extensions.swiftmodule %s -primary-file %S/Inputs/xref-generic-params-other-extensions.swift -module-name extensions
+// RUN: %target-swift-frontend -merge-modules -emit-module -o %t/extensions.swiftmodule %t/a-extensions.swiftmodule %t/b-extensions.swiftmodule -module-name extensions
+// RUN: %target-swift-ide-test -print-module -module-to-print=extensions -I %t -source-filename=x | %FileCheck %s
+
+// RUN: %target-swift-frontend -emit-module -o %t/a-extensions_mixed.swiftmodule -primary-file %s %S/Inputs/xref-generic-params-other-extensions-mixed.swift -module-name extensions_mixed
+// RUN: %target-swift-frontend -emit-module -o %t/b-extensions_mixed.swiftmodule %s -primary-file %S/Inputs/xref-generic-params-other-extensions-mixed.swift -module-name extensions_mixed
+// RUN: %target-swift-frontend -merge-modules -emit-module -o %t/extensions_mixed.swiftmodule %t/a-extensions_mixed.swiftmodule %t/b-extensions_mixed.swiftmodule -module-name extensions_mixed
+// RUN: %target-swift-ide-test -print-module -module-to-print=extensions_mixed -I %t -source-filename=x | %FileCheck %s
+
+// RUN: %target-swift-frontend -emit-module -o %t/a-extensions_constrained.swiftmodule -primary-file %s %S/Inputs/xref-generic-params-other-extensions-constrained.swift -module-name extensions_constrained
+// RUN: %target-swift-frontend -emit-module -o %t/b-extensions_constrained.swiftmodule %s -primary-file %S/Inputs/xref-generic-params-other-extensions-constrained.swift -module-name extensions_constrained
+// RUN: %target-swift-frontend -merge-modules -emit-module -o %t/extensions_constrained.swiftmodule %t/a-extensions_constrained.swiftmodule %t/b-extensions_constrained.swiftmodule -module-name extensions_constrained
+// RUN: %target-swift-ide-test -print-module -module-to-print=extensions_constrained -I %t -source-filename=x | %FileCheck %s
+
+public struct A: Equatable {}
+public struct B: Equatable {}
+public struct C: Equatable {}
+public struct D: Equatable {}
+
+// CHECK-LABEL: func test(
+public func test(
+// CHECK-SAME: _: OuterNonGeneric.InnerNonGeneric.AliasTy
+  _: OuterNonGeneric.InnerNonGeneric.AliasTy,
+// CHECK-SAME: _: OuterNonGeneric.InnerGeneric<C, D>.AliasTy
+  _: OuterNonGeneric.InnerGeneric<C, D>.AliasTy,
+// CHECK-SAME: _: OuterGeneric<A, B>.InnerNonGeneric.AliasTy
+  _: OuterGeneric<A, B>.InnerNonGeneric.AliasTy,
+// CHECK-SAME: _: OuterGeneric<A, B>.InnerGeneric<C, D>.AliasTy
+  _: OuterGeneric<A, B>.InnerGeneric<C, D>.AliasTy) {}