Emit implementation relationships for remote type -> local interface

internal/implementations/implementations.go

@@ -108,8 +108,9 @@ func AddImplementationRelationships(
 	pkgs loader.PackageLookup,
 	allPackages loader.PackageLookup,
 	symbols *lookup.Global,
-) error {
-	return output.WithProgress("Indexing Implementations", func() error {
+) ([]*scip.SymbolInformation, error) {
+	var externalSymbols []*scip.SymbolInformation
+	err := output.WithProgress("Indexing Implementations", func() error {
 		localInterfaces, localTypes, err := extractInterfacesAndConcreteTypes(pkgs, symbols)
 		if err != nil {
 			return err
@@ -123,7 +124,8 @@ func AddImplementationRelationships(
 
 			remotePackages[pkgID] = pkg
 		}
-		remoteInterfaces, _, err := extractInterfacesAndConcreteTypes(remotePackages, symbols)
+		remoteInterfaces, remoteTypes, err := extractInterfacesAndConcreteTypes(
+			remotePackages, symbols)
 		if err != nil {
 			return err
 		}
@@ -134,15 +136,22 @@ func AddImplementationRelationships(
 		// local type -> remote interface
 		findImplementations(localTypes, remoteInterfaces, symbols)
 
-		// TODO(author: tjdevries, issue: https://github.com/sourcegraph/scip-go/issues/64)
-		// We should consider what this would even look like?
-		// I don't think this makes sense the current way that we are emitting
-		// implementations. You wouldn't even catch these anyways when uploading
 		// remote type -> local interface
-		// findImplementations(remoteTypes, localInterfaces, symbols)
+		// We emit these as external symbols so index consumer can merge them.
+		findImplementations(remoteTypes, localInterfaces, symbols)
+
+		// Collect remote type symbols that gained relationships
+		for _, typ := range remoteTypes {
+			if sym, ok := symbols.GetSymbolInformation(typ.Pkg, typ.Ident.Pos()); ok {
+				if len(sym.Relationships) > 0 {
+					externalSymbols = append(externalSymbols, sym)
+				}
+			}
+		}
 
 		return nil
 	})
+	return externalSymbols, err
 }
 
 func implementationsForType(ty ImplDef, tyMethods *intsets.Sparse, interfaceToMethodSet map[*scip.SymbolInformation]*intsets.Sparse) (matching []*scip.SymbolInformation) {

internal/index/scip.go

@@ -98,13 +98,16 @@ func Index(writer func(proto.Message) error, opts config.IndexOpts) error {
 		return err
 	}
 
+	var externalSymbols []*scip.SymbolInformation
 	pathToDocument, globalSymbols := indexVisitPackages(opts, projectPackages, allPackages)
 	if !opts.SkipImplementations {
-		if err := impls.AddImplementationRelationships(
+		implSymbols, err := impls.AddImplementationRelationships(
 			projectPackages, allPackages, globalSymbols,
-		); err != nil {
+		)
+		if err != nil {
 			return err
 		}
+		externalSymbols = implSymbols
 	}
 
 	pkgIDs := slices.Sorted(maps.Keys(projectPackages))
@@ -156,7 +159,18 @@ func Index(writer func(proto.Message) error, opts config.IndexOpts) error {
 
 	output.WithProgressParallel(&wg, "Visiting Project Files", &count, uint64(pkgLen))
 
-	return writeErr
+	if writeErr != nil {
+		return writeErr
+	}
+
+	// Emit external symbols for remote types that implement local interfaces
+	for _, sym := range externalSymbols {
+		if err := writer(sym); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 func indexVisitPackages(

internal/testdata/snapshots/input/pr198/dep/dep.go

@@ -0,0 +1,9 @@
+package dep
+
+import "fmt"
+
+type T struct{}
+
+func (t *T) Bar() {
+	fmt.Println("Bar")
+}

internal/testdata/snapshots/input/pr198/dep/go.mod

@@ -0,0 +1,3 @@
+module github.com/example/dep
+
+go 1.22

internal/testdata/snapshots/input/pr198/go.mod

@@ -0,0 +1,7 @@
+module sg/pr198
+
+go 1.25
+
+require github.com/example/dep v0.0.0
+
+replace github.com/example/dep => ./dep

internal/testdata/snapshots/input/pr198/pr198.go

@@ -0,0 +1,17 @@
+package pr198
+
+import "github.com/example/dep"
+
+// Foo is an interface defined downstream of the type that implements it.
+// The dep.T type (from a dependency) implements Foo, and scip-go should
+// emit an external symbol for dep.T with an IsImplementation relationship
+// pointing to Foo.
+type Foo interface {
+	Bar()
+}
+
+func UseFoo(f Foo) {}
+
+func Example() {
+	UseFoo(&dep.T{})
+}

internal/testdata/snapshots/input/testdata/implementations.go

@@ -34,7 +34,7 @@ type Foo int
 
 func (r Foo) nonExportedMethod() {}
 func (r Foo) ExportedMethod()    {}
-func (r Foo) Close() error       { return nil }
+func (r Foo) ScipTestMethod()    {}
 
 type SharedOne interface {
 	Shared()

internal/testdata/snapshots/input/testdata/implementations_embedded.go

@@ -1,11 +1,13 @@
 package testdata
 
-import "io"
-
 type I3 interface {
-	Close() error
+	ScipTestMethod()
+}
+
+type EmbeddedI3 interface {
+	ScipTestMethod()
 }
 
 type TClose struct {
-	io.Closer
+	EmbeddedI3
 }

internal/testdata/snapshots/output/pr198/external_symbols.txt

@@ -0,0 +1,2 @@
+github.com/example/dep 0.1.test `github.com/example/dep`/T#
+  relationship 0.1.test `sg/pr198`/Foo# implementation

internal/testdata/snapshots/output/pr198/pr198.go

@@ -0,0 +1,52 @@
+  package pr198
+//        ^^^^^ definition 0.1.test `sg/pr198`/
+//              display_name pr198
+//              signature_documentation
+//              > package pr198
+
+  import "github.com/example/dep"
+//        ^^^^^^^^^^^^^^^^^^^^^^ reference github.com/example/dep 0.1.test `github.com/example/dep`/
+
+  // Foo is an interface defined downstream of the type that implements it.
+  // The dep.T type (from a dependency) implements Foo, and scip-go should
+  // emit an external symbol for dep.T with an IsImplementation relationship
+  // pointing to Foo.
+  type Foo interface {
+//     ^^^ definition 0.1.test `sg/pr198`/Foo#
+//         signature_documentation
+//         > type Foo interface{ Bar() }
+//         documentation
+//         > Foo is an interface defined downstream of the type that implements it.
+//         > The dep.T type (from a dependency) implements Foo, and scip-go should
+//         > emit an external symbol for dep.T with an IsImplementation relationship
+//         > pointing to Foo.
+   Bar()
+// ^^^ definition 0.1.test `sg/pr198`/Foo#Bar.
+//     signature_documentation
+//     > func (Foo).Bar()
+  }
+
+//⌄ enclosing_range_start 0.1.test `sg/pr198`/UseFoo().
+  func UseFoo(f Foo) {}
+//     ^^^^^^ definition 0.1.test `sg/pr198`/UseFoo().
+//            signature_documentation
+//            > func UseFoo(f Foo)
+//            ^ definition local 0
+//              display_name f
+//              signature_documentation
+//              > var f Foo
+//              ^^^ reference 0.1.test `sg/pr198`/Foo#
+//                    ⌃ enclosing_range_end 0.1.test `sg/pr198`/UseFoo().
+
+//⌄ enclosing_range_start 0.1.test `sg/pr198`/Example().
+  func Example() {
+//     ^^^^^^^ definition 0.1.test `sg/pr198`/Example().
+//             signature_documentation
+//             > func Example()
+   UseFoo(&dep.T{})
+// ^^^^^^ reference 0.1.test `sg/pr198`/UseFoo().
+//         ^^^ reference github.com/example/dep 0.1.test `github.com/example/dep`/
+//             ^ reference github.com/example/dep 0.1.test `github.com/example/dep`/T#
+  }
+//⌃ enclosing_range_end 0.1.test `sg/pr198`/Example().
+

internal/testdata/snapshots/output/testdata/implementations.go

@@ -112,7 +112,7 @@
 //     ^^^ definition 0.1.test `sg/testdata`/Foo#
 //         signature_documentation
 //         > type Foo int
-//         relationship github.com/golang/go/src go1.22 io/Closer# implementation
+//         relationship 0.1.test `sg/testdata`/EmbeddedI3# implementation
 //         relationship 0.1.test `sg/testdata`/I3# implementation
 //         relationship 0.1.test `sg/testdata`/InterfaceWithExportedMethod# implementation
 //         relationship 0.1.test `sg/testdata`/InterfaceWithNonExportedMethod# implementation
@@ -141,19 +141,19 @@
 //                            > func (Foo).ExportedMethod()
 //                            relationship 0.1.test `sg/testdata`/InterfaceWithExportedMethod#ExportedMethod. implementation
 //                                  ⌃ enclosing_range_end 0.1.test `sg/testdata`/Foo#ExportedMethod().
-//⌄ enclosing_range_start 0.1.test `sg/testdata`/Foo#Close().
-  func (r Foo) Close() error       { return nil }
+//⌄ enclosing_range_start 0.1.test `sg/testdata`/Foo#ScipTestMethod().
+  func (r Foo) ScipTestMethod()    {}
 //      ^ definition local 5
 //        display_name r
 //        signature_documentation
 //        > var r Foo
 //        ^^^ reference 0.1.test `sg/testdata`/Foo#
-//             ^^^^^ definition 0.1.test `sg/testdata`/Foo#Close().
-//                   signature_documentation
-//                   > func (Foo).Close() error
-//                   relationship github.com/golang/go/src go1.22 io/Closer#Close. implementation
-//                   relationship 0.1.test `sg/testdata`/I3#Close. implementation
-//                                              ⌃ enclosing_range_end 0.1.test `sg/testdata`/Foo#Close().
+//             ^^^^^^^^^^^^^^ definition 0.1.test `sg/testdata`/Foo#ScipTestMethod().
+//                            signature_documentation
+//                            > func (Foo).ScipTestMethod()
+//                            relationship 0.1.test `sg/testdata`/EmbeddedI3#ScipTestMethod. implementation
+//                            relationship 0.1.test `sg/testdata`/I3#ScipTestMethod. implementation
+//                                  ⌃ enclosing_range_end 0.1.test `sg/testdata`/Foo#ScipTestMethod().
 
   type SharedOne interface {
 //     ^^^^^^^^^ definition 0.1.test `sg/testdata`/SharedOne#

internal/testdata/snapshots/output/testdata/implementations_embedded.go

@@ -1,30 +1,38 @@
   package testdata
 //        ^^^^^^^^ definition 0.1.test `sg/testdata`/
 
-  import "io"
-//        ^^ reference github.com/golang/go/src go1.22 io/
-
   type I3 interface {
 //     ^^ definition 0.1.test `sg/testdata`/I3#
 //        signature_documentation
-//        > type I3 interface{ Close() error }
-   Close() error
-// ^^^^^ definition 0.1.test `sg/testdata`/I3#Close.
-//       signature_documentation
-//       > func (I3).Close() error
+//        > type I3 interface{ ScipTestMethod() }
+   ScipTestMethod()
+// ^^^^^^^^^^^^^^ definition 0.1.test `sg/testdata`/I3#ScipTestMethod.
+//                signature_documentation
+//                > func (I3).ScipTestMethod()
+  }
+
+  type EmbeddedI3 interface {
+//     ^^^^^^^^^^ definition 0.1.test `sg/testdata`/EmbeddedI3#
+//                signature_documentation
+//                > type EmbeddedI3 interface{ ScipTestMethod() }
+   ScipTestMethod()
+// ^^^^^^^^^^^^^^ definition 0.1.test `sg/testdata`/EmbeddedI3#ScipTestMethod.
+//                signature_documentation
+//                > func (EmbeddedI3).ScipTestMethod()
+//                relationship 0.1.test `sg/testdata`/EmbeddedI3#ScipTestMethod. implementation
+//                relationship 0.1.test `sg/testdata`/I3#ScipTestMethod. implementation
   }
 
   type TClose struct {
 //     ^^^^^^ definition 0.1.test `sg/testdata`/TClose#
 //            signature_documentation
-//            > type TClose struct{ Closer }
-//            relationship github.com/golang/go/src go1.22 io/Closer# implementation
+//            > type TClose struct{ EmbeddedI3 }
+//            relationship 0.1.test `sg/testdata`/EmbeddedI3# implementation
 //            relationship 0.1.test `sg/testdata`/I3# implementation
-   io.Closer
-// ^^ reference github.com/golang/go/src go1.22 io/
-//    ^^^^^^ definition 0.1.test `sg/testdata`/TClose#Closer.
-//           signature_documentation
-//           > struct field Closer io.Closer
-//    ^^^^^^ reference github.com/golang/go/src go1.22 io/Closer#
+   EmbeddedI3
+// ^^^^^^^^^^ definition 0.1.test `sg/testdata`/TClose#EmbeddedI3.
+//            signature_documentation
+//            > struct field EmbeddedI3 sg/testdata.EmbeddedI3
+// ^^^^^^^^^^ reference 0.1.test `sg/testdata`/EmbeddedI3#
   }