reflect: implement NumMethod and Implements

These two functions are needed by the encoding/json package.

Author: aykevl

compiler/interface.go

@@ -72,14 +72,34 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 			structGlobal := c.makeStructTypeFields(typ)
 			references = llvm.ConstBitCast(structGlobal, global.Type())
 		}
-		if !references.IsNil() {
+		methodSet := types.NewMethodSet(typ)
+		numMethods := 0
+		_, isInterface := typ.Underlying().(*types.Interface)
+		for i := 0; i < methodSet.Len(); i++ {
+			// NumMethod (unintentionally) includes unexported methods for
+			// interface types but excludes unexported methods for other types.
+			// This makes sure we're bug-compatible with the Go reflect package.
+			// For a discussion, see:
+			// https://github.com/golang/go/issues/22075 (original bug)
+			// https://github.com/golang/go/issues/42123 (revert of bugfix)
+			if methodSet.At(i).Obj().Exported() || isInterface {
+				numMethods++
+			}
+		}
+		if !references.IsNil() || numMethods != 0 || isInterface {
 			// Set the 'references' field of the runtime.typecodeID struct.
 			globalValue := llvm.ConstNull(global.Type().ElementType())
-			globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
+			if !references.IsNil() {
+				globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
+			}
 			if length != 0 {
 				lengthValue := llvm.ConstInt(c.uintptrType, uint64(length), false)
 				globalValue = llvm.ConstInsertValue(globalValue, lengthValue, []uint32{1})
 			}
+			if numMethods != 0 {
+				numMethodsValue := llvm.ConstInt(c.uintptrType, uint64(numMethods), false)
+				globalValue = llvm.ConstInsertValue(globalValue, numMethodsValue, []uint32{2})
+			}
 			global.SetInitializer(globalValue)
 			global.SetLinkage(llvm.PrivateLinkage)
 		}
@@ -187,7 +207,7 @@ func getTypeCodeName(t types.Type) string {
 	case *types.Interface:
 		methods := make([]string, t.NumMethods())
 		for i := 0; i < t.NumMethods(); i++ {
-			methods[i] = getTypeCodeName(t.Method(i).Type())
+			methods[i] = t.Method(i).Name() + ":" + getTypeCodeName(t.Method(i).Type())
 		}
 		return "interface:" + "{" + strings.Join(methods, ",") + "}"
 	case *types.Map:

src/reflect/sidetables.go

@@ -4,12 +4,22 @@ import (
 	"unsafe"
 )
 
+// This stores the number of methods (for Type.NumMethod()) for each named basic
+// type. It is indexed by the named type number.
+//go:extern reflect.namedBasicNumMethodSidetable
+var namedBasicNumMethodSidetable byte
+
 // This stores a varint for each named type. Named types are identified by their
 // name instead of by their type. The named types stored in this struct are
-// non-basic types: pointer, struct, and channel.
+// non-basic types: pointer, struct, channel, and interface.
 //go:extern reflect.namedNonBasicTypesSidetable
 var namedNonBasicTypesSidetable uintptr
 
+// This stores the number of methods (for Type.NumMethods()) for each named
+// non-basic type. It is indexed by the named type number.
+//go:extern reflect.namedNonBasicNumMethodSidetable
+var namedNonBasicNumMethodSidetable byte
+
 //go:extern reflect.structTypesSidetable
 var structTypesSidetable byte
 
@@ -19,6 +29,9 @@ var structNamesSidetable byte
 //go:extern reflect.arrayTypesSidetable
 var arrayTypesSidetable byte
 
+//go:extern reflect.interfaceTypesSidetable
+var interfaceTypesSidetable byte
+
 // readStringSidetable reads a string from the given table (like
 // structNamesSidetable) and returns this string. No heap allocation is
 // necessary because it makes the string point directly to the raw bytes of the

src/reflect/type.go

@@ -146,6 +146,20 @@ func (t Type) Kind() Kind {
 	}
 }
 
+// isBasic returns true if (and only if) this is a basic type.
+func (t Type) isBasic() bool {
+	return t%2 == 0
+}
+
+// isNamed returns true if (and only if) this is a named type.
+func (t Type) isNamed() bool {
+	if t.isBasic() {
+		return t>>6 != 0
+	} else {
+		return (t>>4)%2 != 0
+	}
+}
+
 // Elem returns the element type for channel, slice and array types, the
 // pointed-to value for pointer types, and the key type for map types.
 func (t Type) Elem() Type {
@@ -170,7 +184,7 @@ func (t Type) Elem() Type {
 func (t Type) stripPrefix() Type {
 	// Look at the 'n' bit in the type code (see the top of this file) to see
 	// whether this is a named type.
-	if (t>>4)%2 != 0 {
+	if t.isNamed() {
 		// This is a named type. The data is stored in a sidetable.
 		namedTypeNum := t >> 5
 		n := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&namedNonBasicTypesSidetable)) + uintptr(namedTypeNum)*unsafe.Sizeof(uintptr(0))))
@@ -188,7 +202,11 @@ func (t Type) Field(i int) StructField {
 	}
 	structIdentifier := t.stripPrefix()
 
-	numField, p := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&structTypesSidetable)) + uintptr(structIdentifier)))
+	// Skip past the NumMethod field.
+	_, p := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&structTypesSidetable)) + uintptr(structIdentifier)))
+
+	// Read the NumField field.
+	numField, p := readVarint(p)
 	if uint(i) >= uint(numField) {
 		panic("reflect: field index out of range")
 	}
@@ -287,7 +305,10 @@ func (t Type) NumField() int {
 		panic(&TypeError{"NumField"})
 	}
 	structIdentifier := t.stripPrefix()
-	n, _ := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&structTypesSidetable)) + uintptr(structIdentifier)))
+	// Skip past the NumMethod field.
+	_, p := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&structTypesSidetable)) + uintptr(structIdentifier)))
+	// Read the NumField field.
+	n, _ := readVarint(p)
 	return int(n)
 }
 
@@ -405,10 +426,23 @@ func (t Type) AssignableTo(u Type) bool {
 }
 
 func (t Type) Implements(u Type) bool {
-	if t.Kind() != Interface {
+	if u.Kind() != Interface {
 		panic("reflect: non-interface type passed to Type.Implements")
 	}
-	return u.AssignableTo(t)
+	if u.NumMethod() == 0 {
+		// Empty interface (not even unexported methods, see NumNethod
+		// implementation comments), therefore implements any type.
+		return true
+	}
+	// Type u has (possibly unexported) methods.
+	if t.Kind() == Interface && t.NumMethod() == 0 {
+		// Type t has no methods (not even unexported methods since it is an
+		// interface), while u has. Therefore, t cannot implement u.
+		return false
+	}
+	// Now we'd have to compare individual methods.
+	// This has not yet been implemented.
+	panic("unimplemented: (reflect.Type).Implements()")
 }
 
 // Comparable returns whether values of this type can be compared to each other.
@@ -454,7 +488,36 @@ func (t Type) ConvertibleTo(u Type) bool {
 }
 
 func (t Type) NumMethod() int {
-	panic("unimplemented: (reflect.Type).NumMethod()")
+	if t.isBasic() {
+		if !t.isNamed() {
+			// Not a named type, so can't have methods.
+			return 0
+		}
+		// Named type methods are stored in a sidetable.
+		namedTypeNum := t >> 6
+		return int(*(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(&namedBasicNumMethodSidetable)) + uintptr(namedTypeNum) - 1)))
+	} else {
+		if !t.isNamed() {
+			// Most non-named types cannot have methods. However, structs can
+			// because they can embed named values.
+			switch t.Kind() {
+			case Struct:
+				structIdentifier := t.stripPrefix()
+				numMethod, _ := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&structTypesSidetable)) + uintptr(structIdentifier)))
+				return int(numMethod)
+			case Interface:
+				interfaceIdentifier := t.stripPrefix()
+				numMethod, _ := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&interfaceTypesSidetable)) + uintptr(interfaceIdentifier)))
+				return int(numMethod)
+			default:
+				// This type cannot have methods.
+				return 0
+			}
+		}
+		// Named non-basic type, so read the number of methods from a sidetable.
+		namedTypeNum := t >> 5
+		return int(*(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(&namedNonBasicNumMethodSidetable)) + uintptr(namedTypeNum))))
+	}
 }
 
 func (t Type) Name() string {

src/reflect/value.go

@@ -532,6 +532,10 @@ func maskAndShift(value, offset, size uintptr) uintptr {
 	return (uintptr(value) >> (offset * 8)) & mask
 }
 
+func (v Value) NumMethod() int {
+	return v.Type().NumMethod()
+}
+
 func (v Value) MapKeys() []Value {
 	panic("unimplemented: (reflect.Value).MapKeys()")
 }

src/runtime/interface.go

@@ -107,6 +107,9 @@ type typecodeID struct {
 
 	// The array length, for array types.
 	length uintptr
+
+	// Number of methods on this type. Usually 0 for non-named types.
+	numMethods uintptr
 }
 
 // structField is used by the compiler to pass information to the interface

testdata/reflect.go

@@ -26,8 +26,18 @@ type (
 		next *linkedList `description:"chain"`
 		foo  int
 	}
+	myitf interface {
+		Foo()
+		bar()
+		baz()
+	}
 )
 
+// To test Type.NumMethod.
+func (n myint) foo() {}
+func (n myint) bar() {}
+func (n myint) Baz() {}
+
 func main() {
 	println("matching types")
 	println(reflect.TypeOf(int(3)) == reflect.TypeOf(int(5)))
@@ -111,6 +121,16 @@ func main() {
 		&linkedList{
 			foo: 42,
 		},
+		// interfaces
+		struct {
+			a interface{}
+			b interface {
+				Foo()
+				bar()
+			}
+			c myitf
+			d *myitf
+		}{},
 	} {
 		showValue(reflect.ValueOf(v), "")
 	}
@@ -284,6 +304,9 @@ func showValue(rv reflect.Value, indent string) {
 	if !rt.Comparable() {
 		print(" comparable=false")
 	}
+	if rt.NumMethod() != 0 {
+		print(" methods=", rt.NumMethod())
+	}
 	println()
 	switch rt.Kind() {
 	case reflect.Bool:
@@ -339,7 +362,9 @@ func showValue(rv reflect.Value, indent string) {
 		for i := 0; i < rv.NumField(); i++ {
 			field := rt.Field(i)
 			println(indent+"  field:", i, field.Name)
-			println(indent+"  tag:", field.Tag)
+			if field.Tag != "" {
+				println(indent+"  tag:", field.Tag)
+			}
 			println(indent+"  embedded:", field.Anonymous)
 			showValue(rv.Field(i), indent+"  ")
 		}

testdata/reflect.txt

@@ -51,7 +51,7 @@ reflect type: complex64
   complex: (+1.200000e+000+3.000000e-001i)
 reflect type: complex128
   complex: (+1.300000e+000+4.000000e-001i)
-reflect type: int
+reflect type: int methods=1
   int: 32
 reflect type: string
   string: foo 3
@@ -77,7 +77,7 @@ reflect type: ptr
 reflect type: ptr
   pointer: true interface
   nil: false
-  reflect type: interface settable=true
+  reflect type: interface settable=true methods=1
     interface
     nil: true
 reflect type: ptr
@@ -230,28 +230,24 @@ reflect type: map comparable=false
   nil: false
 reflect type: struct
   struct: 0
-reflect type: struct
+reflect type: struct methods=1
   struct: 1
   field: 0 error
-  tag: 
   embedded: true
-  reflect type: interface
+  reflect type: interface methods=1
     interface
     nil: true
 reflect type: struct
   struct: 3
   field: 0 a
-  tag: 
   embedded: false
   reflect type: uint8
     uint: 42
   field: 1 b
-  tag: 
   embedded: false
   reflect type: int16
     int: 321
   field: 2 c
-  tag: 
   embedded: false
   reflect type: int8
     int: 123
@@ -263,27 +259,22 @@ reflect type: struct comparable=false
   reflect type: int
     int: 5
   field: 1 some
-  tag: 
   embedded: false
   reflect type: struct
     struct: 2
     field: 0 X
-    tag: 
     embedded: false
     reflect type: int16
       int: -5
     field: 1 Y
-    tag: 
     embedded: false
     reflect type: int16
       int: 3
   field: 2 zero
-  tag: 
   embedded: false
   reflect type: struct
     struct: 0
   field: 3 buf
-  tag: 
   embedded: false
   reflect type: slice comparable=false
     slice: uint8 2 2
@@ -296,7 +287,6 @@ reflect type: struct comparable=false
     reflect type: uint8
       uint: 111
   field: 4 Buf
-  tag: 
   embedded: false
   reflect type: slice comparable=false
     slice: uint8 1 1
@@ -317,10 +307,31 @@ reflect type: ptr
       pointer: false struct
       nil: true
     field: 1 foo
-    tag: 
     embedded: false
     reflect type: int
       int: 42
+reflect type: struct
+  struct: 4
+  field: 0 a
+  embedded: false
+  reflect type: interface
+    interface
+    nil: true
+  field: 1 b
+  embedded: false
+  reflect type: interface methods=2
+    interface
+    nil: true
+  field: 2 c
+  embedded: false
+  reflect type: interface methods=3
+    interface
+    nil: true
+  field: 3 d
+  embedded: false
+  reflect type: ptr
+    pointer: false interface
+    nil: true
 
 sizes:
 int8 1 8