oracle: when 'implements' is invoked on a method, show related methods, not types.

Fixes #9972

Change-Id: I25b65a64dcc4d551be3db8566783a9d23d410a2e
Reviewed-on: https://go-review.googlesource.com/5860
Reviewed-by: David Crawshaw <crawshaw@golang.org>

10 files changed, 545 insertions, 42 deletions

diff --git a/cmd/oracle/main.go b/cmd/oracle/main.go
index 294bde7..96efcb6 100644
--- a/cmd/oracle/main.go
+++ b/cmd/oracle/main.go
@@ -59,7 +59,7 @@ The mode argument determines the query to perform:
 	callstack 	show path from callgraph root to selected function
 	describe  	describe selected syntax: definition, methods, etc
 	freevars  	show free variables of selection
-	implements	show 'implements' relation for selected type
+	implements	show 'implements' relation for selected type or method
 	peers     	show send/receive corresponding to selected channel op
 	referrers 	show all refs to entity denoted by selected identifier
 	what		show basic information about the selected syntax node
diff --git a/oracle/describe.go b/oracle/describe.go
index 1c329d0..9c21017 100644
--- a/oracle/describe.go
+++ b/oracle/describe.go
@@ -215,13 +215,6 @@ func findInterestingNode(pkginfo *loader.PackageInfo, path []ast.Node) ([]ast.No
 				return path, actionExpr
 
 			case *types.Func:
-				// For f in 'interface {f()}', return the interface type, for now.
-				if _, ok := path[1].(*ast.Field); ok {
-					_ = path[2].(*ast.FieldList) // assertion
-					if _, ok := path[3].(*ast.InterfaceType); ok {
-						return path[3:], actionType
-					}
-				}
 				return path, actionExpr
 
 			case *types.Builtin:
@@ -737,10 +730,14 @@ func isAccessibleFrom(obj types.Object, pkg *types.Package) bool {
 func methodsToSerial(this *types.Package, methods []*types.Selection, fset *token.FileSet) []serial.DescribeMethod {
 	var jmethods []serial.DescribeMethod
 	for _, meth := range methods {
-		jmethods = append(jmethods, serial.DescribeMethod{
-			Name: types.SelectionString(this, meth),
-			Pos:  fset.Position(meth.Obj().Pos()).String(),
-		})
+		var ser serial.DescribeMethod
+		if meth != nil { // may contain nils when called by implements (on a method)
+			ser = serial.DescribeMethod{
+				Name: types.SelectionString(this, meth),
+				Pos:  fset.Position(meth.Obj().Pos()).String(),
+			}
+		}
+		jmethods = append(jmethods, ser)
 	}
 	return jmethods
 }
diff --git a/oracle/implements.go b/oracle/implements.go
index 8e54dea..1ad80b4 100644
--- a/oracle/implements.go
+++ b/oracle/implements.go
@@ -17,18 +17,35 @@ import (
 )
 
 // Implements displays the "implements" relation as it pertains to the
-// selected type.
+// selected type.  If the selection is a method, 'implements' displays
+// the corresponding methods of the types that would have been reported
+// by an implements query on the receiver type.
 //
 func implements(o *Oracle, qpos *QueryPos) (queryResult, error) {
 	// Find the selected type.
-	// TODO(adonovan): fix: make it work on qualified Idents too.
 	path, action := findInterestingNode(qpos.info, qpos.path)
-	if action != actionType {
-		return nil, fmt.Errorf("no type here")
+
+	var method *types.Func
+	var T types.Type // selected type (receiver if method != nil)
+
+	switch action {
+	case actionExpr:
+		// method?
+		if id, ok := path[0].(*ast.Ident); ok {
+			if obj, ok := qpos.info.ObjectOf(id).(*types.Func); ok {
+				recv := obj.Type().(*types.Signature).Recv()
+				if recv == nil {
+					return nil, fmt.Errorf("this function is not a method")
+				}
+				method = obj
+				T = recv.Type()
+			}
+		}
+	case actionType:
+		T = qpos.info.TypeOf(path[0].(ast.Expr))
 	}
-	T := qpos.info.TypeOf(path[0].(ast.Expr))
 	if T == nil {
-		return nil, fmt.Errorf("no type here")
+		return nil, fmt.Errorf("no type or method here")
 	}
 
 	// Find all named types, even local types (which can have
@@ -102,52 +119,128 @@ func implements(o *Oracle, qpos *QueryPos) (queryResult, error) {
 	sort.Sort(typesByString(from))
 	sort.Sort(typesByString(fromPtr))
 
-	return &implementsResult{T, pos, to, from, fromPtr}, nil
+	var toMethod, fromMethod, fromPtrMethod []*types.Selection // contain nils
+	if method != nil {
+		for _, t := range to {
+			toMethod = append(toMethod,
+				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
+		}
+		for _, t := range from {
+			fromMethod = append(fromMethod,
+				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
+		}
+		for _, t := range fromPtr {
+			fromPtrMethod = append(fromPtrMethod,
+				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
+		}
+	}
+
+	return &implementsResult{qpos, T, pos, to, from, fromPtr, method, toMethod, fromMethod, fromPtrMethod}, nil
 }
 
 type implementsResult struct {
+	qpos *QueryPos
+
 	t       types.Type   // queried type (not necessarily named)
 	pos     interface{}  // pos of t (*types.Name or *QueryPos)
 	to      []types.Type // named or ptr-to-named types assignable to interface T
 	from    []types.Type // named interfaces assignable from T
 	fromPtr []types.Type // named interfaces assignable only from *T
+
+	// if a method was queried:
+	method        *types.Func        // queried method
+	toMethod      []*types.Selection // method of type to[i], if any
+	fromMethod    []*types.Selection // method of type from[i], if any
+	fromPtrMethod []*types.Selection // method of type fromPtrMethod[i], if any
 }
 
 func (r *implementsResult) display(printf printfFunc) {
+	relation := "is implemented by"
+
+	meth := func(sel *types.Selection) {
+		if sel != nil {
+			printf(sel.Obj(), "\t%s method (%s).%s",
+				relation, r.qpos.TypeString(sel.Recv()), sel.Obj().Name())
+		}
+	}
+
 	if isInterface(r.t) {
 		if types.NewMethodSet(r.t).Len() == 0 { // TODO(adonovan): cache mset
 			printf(r.pos, "empty interface type %s", r.t)
 			return
 		}
 
-		printf(r.pos, "interface type %s", r.t)
-		// Show concrete types first; use two passes.
-		for _, sub := range r.to {
+		if r.method == nil {
+			printf(r.pos, "interface type %s", r.t)
+		} else {
+			printf(r.method, "abstract method %s", r.qpos.ObjectString(r.method))
+		}
+
+		// Show concrete types (or methods) first; use two passes.
+		for i, sub := range r.to {
 			if !isInterface(sub) {
-				printf(deref(sub).(*types.Named).Obj(), "\tis implemented by %s type %s",
-					typeKind(sub), sub)
+				if r.method == nil {
+					printf(deref(sub).(*types.Named).Obj(), "\t%s %s type %s",
+						relation, typeKind(sub), sub)
+				} else {
+					meth(r.toMethod[i])
+				}
 			}
 		}
-		for _, sub := range r.to {
+		for i, sub := range r.to {
 			if isInterface(sub) {
-				printf(deref(sub).(*types.Named).Obj(), "\tis implemented by %s type %s", typeKind(sub), sub)
+				if r.method == nil {
+					printf(sub.(*types.Named).Obj(), "\t%s %s type %s",
+						relation, typeKind(sub), sub)
+				} else {
+					meth(r.toMethod[i])
+				}
 			}
 		}
 
-		for _, super := range r.from {
-			printf(super.(*types.Named).Obj(), "\timplements %s", super)
+		relation = "implements"
+		for i, super := range r.from {
+			if r.method == nil {
+				printf(super.(*types.Named).Obj(), "\t%s %s", relation, super)
+			} else {
+				meth(r.fromMethod[i])
+			}
 		}
 	} else {
+		relation = "implements"
+
 		if r.from != nil {
-			printf(r.pos, "%s type %s", typeKind(r.t), r.t)
-			for _, super := range r.from {
-				printf(super.(*types.Named).Obj(), "\timplements %s", super)
+			if r.method == nil {
+				printf(r.pos, "%s type %s", typeKind(r.t), r.t)
+			} else {
+				printf(r.method, "concrete method %s",
+					r.qpos.ObjectString(r.method))
+			}
+			for i, super := range r.from {
+				if r.method == nil {
+					printf(super.(*types.Named).Obj(), "\t%s %s",
+						relation, super)
+				} else {
+					meth(r.fromMethod[i])
+				}
 			}
 		}
 		if r.fromPtr != nil {
-			printf(r.pos, "pointer type *%s", r.t)
-			for _, psuper := range r.fromPtr {
-				printf(psuper.(*types.Named).Obj(), "\timplements %s", psuper)
+			if r.method == nil {
+				printf(r.pos, "pointer type *%s", r.t)
+			} else {
+				// TODO(adonovan): de-dup (C).f and (*C).f implementing (I).f.
+				printf(r.method, "concrete method %s",
+					r.qpos.ObjectString(r.method))
+			}
+
+			for i, psuper := range r.fromPtr {
+				if r.method == nil {
+					printf(psuper.(*types.Named).Obj(), "\t%s %s",
+						relation, psuper)
+				} else {
+					meth(r.fromPtrMethod[i])
+				}
 			}
 		} else if r.from == nil {
 			printf(r.pos, "%s type %s implements only interface{}", typeKind(r.t), r.t)
@@ -157,10 +250,19 @@ func (r *implementsResult) display(printf printfFunc) {
 
 func (r *implementsResult) toSerial(res *serial.Result, fset *token.FileSet) {
 	res.Implements = &serial.Implements{
-		T:                 makeImplementsType(r.t, fset),
-		AssignableTo:      makeImplementsTypes(r.to, fset),
-		AssignableFrom:    makeImplementsTypes(r.from, fset),
-		AssignableFromPtr: makeImplementsTypes(r.fromPtr, fset),
+		T:                       makeImplementsType(r.t, fset),
+		AssignableTo:            makeImplementsTypes(r.to, fset),
+		AssignableFrom:          makeImplementsTypes(r.from, fset),
+		AssignableFromPtr:       makeImplementsTypes(r.fromPtr, fset),
+		AssignableToMethod:      methodsToSerial(r.qpos.info.Pkg, r.toMethod, fset),
+		AssignableFromMethod:    methodsToSerial(r.qpos.info.Pkg, r.fromMethod, fset),
+		AssignableFromPtrMethod: methodsToSerial(r.qpos.info.Pkg, r.fromPtrMethod, fset),
+	}
+	if r.method != nil {
+		res.Implements.Method = &serial.DescribeMethod{
+			Name: r.qpos.ObjectString(r.method),
+			Pos:  fset.Position(r.method.Pos()).String(),
+		}
 	}
 }
 
diff --git a/oracle/oracle_test.go b/oracle/oracle_test.go
index bbceb60..fe43fc2 100644
--- a/oracle/oracle_test.go
+++ b/oracle/oracle_test.go
@@ -208,6 +208,7 @@ func TestOracle(t *testing.T) {
 		"testdata/src/main/describe.go",
 		"testdata/src/main/freevars.go",
 		"testdata/src/main/implements.go",
+		"testdata/src/main/implements-methods.go",
 		"testdata/src/main/imports.go",
 		"testdata/src/main/peers.go",
 		"testdata/src/main/pointsto.go",
@@ -221,6 +222,7 @@ func TestOracle(t *testing.T) {
 		"testdata/src/main/peers-json.go",
 		"testdata/src/main/describe-json.go",
 		"testdata/src/main/implements-json.go",
+		"testdata/src/main/implements-methods-json.go",
 		"testdata/src/main/pointsto-json.go",
 		"testdata/src/main/referrers-json.go",
 		"testdata/src/main/what-json.go",
diff --git a/oracle/serial/serial.go b/oracle/serial/serial.go
index 6432b61..86ccb02 100644
--- a/oracle/serial/serial.go
+++ b/oracle/serial/serial.go
@@ -101,7 +101,6 @@ type FreeVar struct {
 }
 
 // An Implements contains the result of an 'implements' query.
-
 // It describes the queried type, the set of named non-empty interface
 // types to which it is assignable, and the set of named/*named types
 // (concrete or non-empty interface) which may be assigned to it.
@@ -111,6 +110,15 @@ type Implements struct {
 	AssignableTo      []ImplementsType `json:"to,omitempty"`      // types assignable to T
 	AssignableFrom    []ImplementsType `json:"from,omitempty"`    // interface types assignable from T
 	AssignableFromPtr []ImplementsType `json:"fromptr,omitempty"` // interface types assignable only from *T
+
+	// The following fields are set only if the query was a method.
+	// Assignable{To,From,FromPtr}Method[i] is the corresponding
+	// method of type Assignable{To,From,FromPtr}[i], or blank
+	// {"",""} if that type lacks the method.
+	Method                  *DescribeMethod  `json:"method,omitempty"` //  the queried method
+	AssignableToMethod      []DescribeMethod `json:"to_method,omitempty"`
+	AssignableFromMethod    []DescribeMethod `json:"from_method,omitempty"`
+	AssignableFromPtrMethod []DescribeMethod `json:"fromptr_method,omitempty"`
 }
 
 // An ImplementsType describes a single type as part of an 'implements' query.
diff --git a/oracle/testdata/src/main/describe.golden b/oracle/testdata/src/main/describe.golden
index 3f305d4..33d751a 100644
--- a/oracle/testdata/src/main/describe.golden
+++ b/oracle/testdata/src/main/describe.golden
@@ -167,7 +167,5 @@ Method set:
 	method (I) f()
 
 -------- @describe def-imethod-I.f --------
-type interface{f()}
-Method set:
-	method (interface{f()}) f()
+definition of interface method func (I).f()
 
diff --git a/oracle/testdata/src/main/implements-methods-json.go b/oracle/testdata/src/main/implements-methods-json.go
new file mode 100644
index 0000000..507dca5
--- /dev/null
+++ b/oracle/testdata/src/main/implements-methods-json.go
@@ -0,0 +1,38 @@
+package main
+
+// Tests of 'implements' query applied to methods, -output=json.
+// See go.tools/oracle/oracle_test.go for explanation.
+// See implements-methods.golden for expected query results.
+
+import _ "lib"
+import _ "sort"
+
+func main() {
+}
+
+type F interface {
+	f() // @implements F.f "f"
+}
+
+type FG interface {
+	f()       // @implements FG.f "f"
+	g() []int // @implements FG.g "g"
+}
+
+type C int
+type D struct{}
+
+func (c *C) f() {} // @implements *C.f "f"
+func (d D) f()  {} // @implements D.f "f"
+
+func (d *D) g() []int { return nil } // @implements *D.g "g"
+
+type sorter []int
+
+func (sorter) Len() int           { return 0 } // @implements Len "Len"
+func (sorter) Less(i, j int) bool { return false }
+func (sorter) Swap(i, j int)      {}
+
+type I interface {
+	Method(*int) *int // @implements I.Method "Method"
+}
diff --git a/oracle/testdata/src/main/implements-methods-json.golden b/oracle/testdata/src/main/implements-methods-json.golden
new file mode 100644
index 0000000..a925caa
--- /dev/null
+++ b/oracle/testdata/src/main/implements-methods-json.golden
@@ -0,0 +1,283 @@
+-------- @implements F.f --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.F",
+			"pos": "testdata/src/main/implements-methods-json.go:13:6",
+			"kind": "interface"
+		},
+		"to": [
+			{
+				"name": "*main.C",
+				"pos": "testdata/src/main/implements-methods-json.go:22:6",
+				"kind": "pointer"
+			},
+			{
+				"name": "main.D",
+				"pos": "testdata/src/main/implements-methods-json.go:23:6",
+				"kind": "struct"
+			},
+			{
+				"name": "main.FG",
+				"pos": "testdata/src/main/implements-methods-json.go:17:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (F).f()",
+			"pos": "testdata/src/main/implements-methods-json.go:14:2"
+		},
+		"to_method": [
+			{
+				"name": "method (*C) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:25:13"
+			},
+			{
+				"name": "method (D) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:26:12"
+			},
+			{
+				"name": "method (FG) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:18:2"
+			}
+		]
+	}
+}-------- @implements FG.f --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.FG",
+			"pos": "testdata/src/main/implements-methods-json.go:17:6",
+			"kind": "interface"
+		},
+		"to": [
+			{
+				"name": "*main.D",
+				"pos": "testdata/src/main/implements-methods-json.go:23:6",
+				"kind": "pointer"
+			}
+		],
+		"from": [
+			{
+				"name": "main.F",
+				"pos": "testdata/src/main/implements-methods-json.go:13:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (FG).f()",
+			"pos": "testdata/src/main/implements-methods-json.go:18:2"
+		},
+		"to_method": [
+			{
+				"name": "method (*D) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:26:12"
+			}
+		],
+		"from_method": [
+			{
+				"name": "method (F) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:14:2"
+			}
+		]
+	}
+}-------- @implements FG.g --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.FG",
+			"pos": "testdata/src/main/implements-methods-json.go:17:6",
+			"kind": "interface"
+		},
+		"to": [
+			{
+				"name": "*main.D",
+				"pos": "testdata/src/main/implements-methods-json.go:23:6",
+				"kind": "pointer"
+			}
+		],
+		"from": [
+			{
+				"name": "main.F",
+				"pos": "testdata/src/main/implements-methods-json.go:13:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (FG).g() []int",
+			"pos": "testdata/src/main/implements-methods-json.go:19:2"
+		},
+		"to_method": [
+			{
+				"name": "method (*D) g() []int",
+				"pos": "testdata/src/main/implements-methods-json.go:28:13"
+			}
+		],
+		"from_method": [
+			{
+				"name": "",
+				"pos": ""
+			}
+		]
+	}
+}-------- @implements *C.f --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "*main.C",
+			"pos": "testdata/src/main/implements-methods-json.go:22:6",
+			"kind": "pointer"
+		},
+		"from": [
+			{
+				"name": "main.F",
+				"pos": "testdata/src/main/implements-methods-json.go:13:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (*C).f()",
+			"pos": "testdata/src/main/implements-methods-json.go:25:13"
+		},
+		"from_method": [
+			{
+				"name": "method (F) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:14:2"
+			}
+		]
+	}
+}-------- @implements D.f --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.D",
+			"pos": "testdata/src/main/implements-methods-json.go:23:6",
+			"kind": "struct"
+		},
+		"from": [
+			{
+				"name": "main.F",
+				"pos": "testdata/src/main/implements-methods-json.go:13:6",
+				"kind": "interface"
+			}
+		],
+		"fromptr": [
+			{
+				"name": "main.FG",
+				"pos": "testdata/src/main/implements-methods-json.go:17:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (D).f()",
+			"pos": "testdata/src/main/implements-methods-json.go:26:12"
+		},
+		"from_method": [
+			{
+				"name": "method (F) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:14:2"
+			}
+		],
+		"fromptr_method": [
+			{
+				"name": "method (FG) f()",
+				"pos": "testdata/src/main/implements-methods-json.go:18:2"
+			}
+		]
+	}
+}-------- @implements *D.g --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "*main.D",
+			"pos": "testdata/src/main/implements-methods-json.go:23:6",
+			"kind": "pointer"
+		},
+		"from": [
+			{
+				"name": "main.F",
+				"pos": "testdata/src/main/implements-methods-json.go:13:6",
+				"kind": "interface"
+			},
+			{
+				"name": "main.FG",
+				"pos": "testdata/src/main/implements-methods-json.go:17:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (*D).g() []int",
+			"pos": "testdata/src/main/implements-methods-json.go:28:13"
+		},
+		"from_method": [
+			{
+				"name": "",
+				"pos": ""
+			},
+			{
+				"name": "method (FG) g() []int",
+				"pos": "testdata/src/main/implements-methods-json.go:19:2"
+			}
+		]
+	}
+}-------- @implements Len --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.sorter",
+			"pos": "testdata/src/main/implements-methods-json.go:30:6",
+			"kind": "slice"
+		},
+		"from": [
+			{
+				"name": "sort.Interface",
+				"pos": "/usr/local/google/home/adonovan/go/src/sort/sort.go:12:6",
+				"kind": "interface"
+			}
+		],
+		"method": {
+			"name": "func (sorter).Len() int",
+			"pos": "testdata/src/main/implements-methods-json.go:32:15"
+		},
+		"from_method": [
+			{
+				"name": "method (sort.Interface) Len() int",
+				"pos": "/usr/local/google/home/adonovan/go/src/sort/sort.go:14:2"
+			}
+		]
+	}
+}-------- @implements I.Method --------
+{
+	"mode": "implements",
+	"implements": {
+		"type": {
+			"name": "main.I",
+			"pos": "testdata/src/main/implements-methods-json.go:36:6",
+			"kind": "interface"
+		},
+		"to": [
+			{
+				"name": "lib.Type",
+				"pos": "testdata/src/lib/lib.go:3:6",
+				"kind": "basic"
+			}
+		],
+		"method": {
+			"name": "func (I).Method(*int) *int",
+			"pos": "testdata/src/main/implements-methods-json.go:37:2"
+		},
+		"to_method": [
+			{
+				"name": "method (lib.Type) Method(x *int) *int",
+				"pos": "testdata/src/lib/lib.go:5:13"
+			}
+		]
+	}
+}
\ No newline at end of file
diff --git a/oracle/testdata/src/main/implements-methods.go b/oracle/testdata/src/main/implements-methods.go
new file mode 100644
index 0000000..4cc4288
--- /dev/null
+++ b/oracle/testdata/src/main/implements-methods.go
@@ -0,0 +1,38 @@
+package main
+
+// Tests of 'implements' query applied to methods.
+// See go.tools/oracle/oracle_test.go for explanation.
+// See implements-methods.golden for expected query results.
+
+import _ "lib"
+import _ "sort"
+
+func main() {
+}
+
+type F interface {
+	f() // @implements F.f "f"
+}
+
+type FG interface {
+	f()       // @implements FG.f "f"
+	g() []int // @implements FG.g "g"
+}
+
+type C int
+type D struct{}
+
+func (c *C) f() {} // @implements *C.f "f"
+func (d D) f()  {} // @implements D.f "f"
+
+func (d *D) g() []int { return nil } // @implements *D.g "g"
+
+type sorter []int
+
+func (sorter) Len() int           { return 0 } // @implements Len "Len"
+func (sorter) Less(i, j int) bool { return false }
+func (sorter) Swap(i, j int)      {}
+
+type I interface {
+	Method(*int) *int // @implements I.Method "Method"
+}
diff --git a/oracle/testdata/src/main/implements-methods.golden b/oracle/testdata/src/main/implements-methods.golden
new file mode 100644
index 0000000..11ccaf4
--- /dev/null
+++ b/oracle/testdata/src/main/implements-methods.golden
@@ -0,0 +1,37 @@
+-------- @implements F.f --------
+abstract method func (F).f()
+	is implemented by method (*C).f
+	is implemented by method (D).f
+	is implemented by method (FG).f
+
+-------- @implements FG.f --------
+abstract method func (FG).f()
+	is implemented by method (*D).f
+	implements method (F).f
+
+-------- @implements FG.g --------
+abstract method func (FG).g() []int
+	is implemented by method (*D).g
+
+-------- @implements *C.f --------
+concrete method func (*C).f()
+	implements method (F).f
+
+-------- @implements D.f --------
+concrete method func (D).f()
+	implements method (F).f
+concrete method func (D).f()
+	implements method (FG).f
+
+-------- @implements *D.g --------
+concrete method func (*D).g() []int
+	implements method (FG).g
+
+-------- @implements Len --------
+concrete method func (sorter).Len() int
+	implements method (sort.Interface).Len
+
+-------- @implements I.Method --------
+abstract method func (I).Method(*int) *int
+	is implemented by method (lib.Type).Method
+