Add a new conversion path to replace GenericConversionFunc

reflect.Call is very expensive. We currently use a switch block as part
of AddGenericConversionFunc to avoid the bulk of top level a->b
conversion for our primary types. Instead of having these be
handwritten, we should generate them.

The pattern for generating them looks like:

```
scheme.AddConversionFunc(&v1.Type{}, &internal.Type{}, func(a, b interface{}, scope conversion.Scope) error {
  return Convert_v1_Type_to_internal_Type(a.(*v1.Type), b.(*internal.Type), scope)
})
```

which matches AddDefaultObjectFunc (which proved out the approach). The
conversion machinery would then do a simple map lookup and invoke the
function. This bypasses reflect.Call and in the future allows Golang
mid-stack inlining to optimize this code.

As a future step we can drop support for the reflection path and simply
return a nice error "you must write a generator for your type".

staging/src/k8s.io/apimachinery/pkg/conversion/converter.go

@@ -40,7 +40,11 @@ type NameFunc func(t reflect.Type) string
 
 var DefaultNameFunc = func(t reflect.Type) string { return t.Name() }
 
-type GenericConversionFunc func(a, b interface{}, scope Scope) (bool, error)
+// ConversionFunc converts the object a into the object b, reusing arrays or objects
+// or pointers if necessary. It should return an error if the object cannot be converted
+// or if some data is invalid. If you do not wish a and b to share fields or nested
+// objects, you must copy a before calling this function.
+type ConversionFunc func(a, b interface{}, scope Scope) error
 
 // Converter knows how to convert one type to another.
 type Converter struct {
@@ -161,11 +165,15 @@ type Scope interface {
 type FieldMappingFunc func(key string, sourceTag, destTag reflect.StructTag) (source string, dest string)
 
 func NewConversionFuncs() ConversionFuncs {
-	return ConversionFuncs{fns: make(map[typePair]reflect.Value)}
+	return ConversionFuncs{
+		fns:     make(map[typePair]reflect.Value),
+		untyped: make(map[typePair]ConversionFunc),
+	}
 }
 
 type ConversionFuncs struct {
-	fns map[typePair]reflect.Value
+	fns     map[typePair]reflect.Value
+	untyped map[typePair]ConversionFunc
 }
 
 // Add adds the provided conversion functions to the lookup table - they must have the signature
@@ -183,6 +191,21 @@ func (c ConversionFuncs) Add(fns ...interface{}) error {
 	return nil
 }
 
+// AddUntyped adds the provided conversion function to the lookup table for the types that are
+// supplied as a and b. a and b must be pointers or an error is returned. This method overwrites
+// previously defined functions.
+func (c ConversionFuncs) AddUntyped(a, b interface{}, fn ConversionFunc) error {
+	tA, tB := reflect.TypeOf(a), reflect.TypeOf(b)
+	if tA.Kind() != reflect.Ptr {
+		return fmt.Errorf("the type %T must be a pointer to register as an untyped conversion", a)
+	}
+	if tB.Kind() != reflect.Ptr {
+		return fmt.Errorf("the type %T must be a pointer to register as an untyped conversion", b)
+	}
+	c.untyped[typePair{tA, tB}] = fn
+	return nil
+}
+
 // Merge returns a new ConversionFuncs that contains all conversions from
 // both other and c, with other conversions taking precedence.
 func (c ConversionFuncs) Merge(other ConversionFuncs) ConversionFuncs {
@@ -193,6 +216,12 @@ func (c ConversionFuncs) Merge(other ConversionFuncs) ConversionFuncs {
 	for k, v := range other.fns {
 		merged.fns[k] = v
 	}
+	for k, v := range c.untyped {
+		merged.untyped[k] = v
+	}
+	for k, v := range other.untyped {
+		merged.untyped[k] = v
+	}
 	return merged
 }
 
@@ -355,16 +384,32 @@ func verifyConversionFunctionSignature(ft reflect.Type) error {
 //                 // conversion logic...
 //                 return nil
 //          })
+// DEPRECATED: Will be removed in favor of RegisterUntypedConversionFunc
 func (c *Converter) RegisterConversionFunc(conversionFunc interface{}) error {
 	return c.conversionFuncs.Add(conversionFunc)
 }
 
 // Similar to RegisterConversionFunc, but registers conversion function that were
 // automatically generated.
+// DEPRECATED: Will be removed in favor of RegisterGeneratedUntypedConversionFunc
 func (c *Converter) RegisterGeneratedConversionFunc(conversionFunc interface{}) error {
 	return c.generatedConversionFuncs.Add(conversionFunc)
 }
 
+// RegisterUntypedConversionFunc registers a function that converts between a and b by passing objects of those
+// types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
+// any other guarantee.
+func (c *Converter) RegisterUntypedConversionFunc(a, b interface{}, fn ConversionFunc) error {
+	return c.conversionFuncs.AddUntyped(a, b, fn)
+}
+
+// RegisterGeneratedUntypedConversionFunc registers a function that converts between a and b by passing objects of those
+// types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
+// any other guarantee.
+func (c *Converter) RegisterGeneratedUntypedConversionFunc(a, b interface{}, fn ConversionFunc) error {
+	return c.generatedConversionFuncs.AddUntyped(a, b, fn)
+}
+
 // RegisterIgnoredConversion registers a "no-op" for conversion, where any requested
 // conversion between from and to is ignored.
 func (c *Converter) RegisterIgnoredConversion(from, to interface{}) error {
@@ -380,39 +425,6 @@ func (c *Converter) RegisterIgnoredConversion(from, to interface{}) error {
 	return nil
 }
 
-// IsConversionIgnored returns true if the specified objects should be dropped during
-// conversion.
-func (c *Converter) IsConversionIgnored(inType, outType reflect.Type) bool {
-	_, found := c.ignoredConversions[typePair{inType, outType}]
-	return found
-}
-
-func (c *Converter) HasConversionFunc(inType, outType reflect.Type) bool {
-	_, found := c.conversionFuncs.fns[typePair{inType, outType}]
-	return found
-}
-
-func (c *Converter) ConversionFuncValue(inType, outType reflect.Type) (reflect.Value, bool) {
-	value, found := c.conversionFuncs.fns[typePair{inType, outType}]
-	return value, found
-}
-
-// SetStructFieldCopy registers a correspondence. Whenever a struct field is encountered
-// which has a type and name matching srcFieldType and srcFieldName, it wil be copied
-// into the field in the destination struct matching destFieldType & Name, if such a
-// field exists.
-// May be called multiple times, even for the same source field & type--all applicable
-// copies will be performed.
-func (c *Converter) SetStructFieldCopy(srcFieldType interface{}, srcFieldName string, destFieldType interface{}, destFieldName string) error {
-	st := reflect.TypeOf(srcFieldType)
-	dt := reflect.TypeOf(destFieldType)
-	srcKey := typeNamePair{st, srcFieldName}
-	destKey := typeNamePair{dt, destFieldName}
-	c.structFieldDests[srcKey] = append(c.structFieldDests[srcKey], destKey)
-	c.structFieldSources[destKey] = append(c.structFieldSources[destKey], srcKey)
-	return nil
-}
-
 // RegisterInputDefaults registers a field name mapping function, used when converting
 // from maps to structs. Inputs to the conversion methods are checked for this type and a mapping
 // applied automatically if the input matches in. A set of default flags for the input conversion
@@ -468,8 +480,8 @@ func (f FieldMatchingFlags) IsSet(flag FieldMatchingFlags) bool {
 // it is not used by Convert() other than storing it in the scope.
 // Not safe for objects with cyclic references!
 func (c *Converter) Convert(src, dest interface{}, flags FieldMatchingFlags, meta *Meta) error {
+	// TODO: deprecated, will be removed in favor of untyped conversion
 	if len(c.genericConversions) > 0 {
-		// TODO: avoid scope allocation
 		s := &scope{converter: c, flags: flags, meta: meta}
 		for _, fn := range c.genericConversions {
 			if ok, err := fn(src, dest, s); ok {
@@ -495,6 +507,21 @@ func (c *Converter) DefaultConvert(src, dest interface{}, flags FieldMatchingFla
 type conversionFunc func(sv, dv reflect.Value, scope *scope) error
 
 func (c *Converter) doConversion(src, dest interface{}, flags FieldMatchingFlags, meta *Meta, f conversionFunc) error {
+	pair := typePair{reflect.TypeOf(src), reflect.TypeOf(dest)}
+	scope := &scope{
+		converter: c,
+		flags:     flags,
+		meta:      meta,
+	}
+	if fn, ok := c.conversionFuncs.untyped[pair]; ok {
+		return fn(src, dest, scope)
+	}
+	if fn, ok := c.generatedConversionFuncs.untyped[pair]; ok {
+		return fn(src, dest, scope)
+	}
+	// TODO: consider everything past this point deprecated - we want to support only point to point top level
+	// conversions
+
 	dv, err := EnforcePtr(dest)
 	if err != nil {
 		return err
@@ -506,15 +533,10 @@ func (c *Converter) doConversion(src, dest interface{}, flags FieldMatchingFlags
 	if err != nil {
 		return err
 	}
-	s := &scope{
-		converter: c,
-		flags:     flags,
-		meta:      meta,
-	}
 	// Leave something on the stack, so that calls to struct tag getters never fail.
-	s.srcStack.push(scopeStackElem{})
-	s.destStack.push(scopeStackElem{})
-	return f(sv, dv, s)
+	scope.srcStack.push(scopeStackElem{})
+	scope.destStack.push(scopeStackElem{})
+	return f(sv, dv, scope)
 }
 
 // callCustom calls 'custom' with sv & dv. custom must be a conversion function.

staging/src/k8s.io/apimachinery/pkg/conversion/converter_test.go

@@ -732,95 +732,3 @@ func TestConverter_flags(t *testing.T) {
 		}
 	}
 }
-
-func TestConverter_FieldRename(t *testing.T) {
-	type WeirdMeta struct {
-		Name string
-		Type string
-	}
-	type NameMeta struct {
-		Name string
-	}
-	type TypeMeta struct {
-		Type string
-	}
-	type A struct {
-		WeirdMeta
-	}
-	type B struct {
-		TypeMeta
-		NameMeta
-	}
-
-	c := NewConverter(DefaultNameFunc)
-	err := c.SetStructFieldCopy(WeirdMeta{}, "WeirdMeta", TypeMeta{}, "TypeMeta")
-	if err != nil {
-		t.Fatalf("unexpected error %v", err)
-	}
-	err = c.SetStructFieldCopy(WeirdMeta{}, "WeirdMeta", NameMeta{}, "NameMeta")
-	if err != nil {
-		t.Fatalf("unexpected error %v", err)
-	}
-	err = c.SetStructFieldCopy(TypeMeta{}, "TypeMeta", WeirdMeta{}, "WeirdMeta")
-	if err != nil {
-		t.Fatalf("unexpected error %v", err)
-	}
-	err = c.SetStructFieldCopy(NameMeta{}, "NameMeta", WeirdMeta{}, "WeirdMeta")
-	if err != nil {
-		t.Fatalf("unexpected error %v", err)
-	}
-	c.Debug = testLogger(t)
-
-	aVal := &A{
-		WeirdMeta: WeirdMeta{
-			Name: "Foo",
-			Type: "Bar",
-		},
-	}
-
-	bVal := &B{
-		TypeMeta: TypeMeta{"Bar"},
-		NameMeta: NameMeta{"Foo"},
-	}
-
-	table := map[string]struct {
-		from, to, expect interface{}
-		flags            FieldMatchingFlags
-	}{
-		"to": {
-			aVal,
-			&B{},
-			bVal,
-			AllowDifferentFieldTypeNames | SourceToDest | IgnoreMissingFields,
-		},
-		"from": {
-			bVal,
-			&A{},
-			aVal,
-			AllowDifferentFieldTypeNames | SourceToDest,
-		},
-		"toDestFirst": {
-			aVal,
-			&B{},
-			bVal,
-			AllowDifferentFieldTypeNames,
-		},
-		"fromDestFirst": {
-			bVal,
-			&A{},
-			aVal,
-			AllowDifferentFieldTypeNames | IgnoreMissingFields,
-		},
-	}
-
-	for name, item := range table {
-		err := c.Convert(item.from, item.to, item.flags, nil)
-		if err != nil {
-			t.Errorf("%v: unexpected error: %v", name, err)
-			continue
-		}
-		if e, a := item.expect, item.to; !reflect.DeepEqual(e, a) {
-			t.Errorf("%v: unexpected diff: %v", name, diff.ObjectDiff(e, a))
-		}
-	}
-}

staging/src/k8s.io/apimachinery/pkg/runtime/scheme.go

@@ -300,6 +300,7 @@ func (s *Scheme) New(kind schema.GroupVersionKind) (Object, error) {
 // (for two conversion types) to the converter. These functions are checked first during
 // a normal conversion, but are otherwise not called. Use AddConversionFuncs when registering
 // typed conversions.
+// DEPRECATED: Use AddConversionFunc
 func (s *Scheme) AddGenericConversionFunc(fn conversion.GenericConversionFunc) {
 	s.converter.AddGenericConversionFunc(fn)
 }
@@ -366,6 +367,20 @@ func (s *Scheme) AddGeneratedConversionFuncs(conversionFuncs ...interface{}) err
 	return nil
 }
 
+// AddConversionFunc registers a function that converts between a and b by passing objects of those
+// types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
+// any other guarantee.
+func (s *Scheme) AddConversionFunc(a, b interface{}, fn conversion.ConversionFunc) error {
+	return s.converter.RegisterUntypedConversionFunc(a, b, fn)
+}
+
+// AddGeneratedConversionFunc registers a function that converts between a and b by passing objects of those
+// types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
+// any other guarantee.
+func (s *Scheme) AddGeneratedConversionFunc(a, b interface{}, fn conversion.ConversionFunc) error {
+	return s.converter.RegisterGeneratedUntypedConversionFunc(a, b, fn)
+}
+
 // AddFieldLabelConversionFunc adds a conversion function to convert field selectors
 // of the given kind from the given version to internal version representation.
 func (s *Scheme) AddFieldLabelConversionFunc(gvk schema.GroupVersionKind, conversionFunc FieldLabelConversionFunc) error {
@@ -373,14 +388,6 @@ func (s *Scheme) AddFieldLabelConversionFunc(gvk schema.GroupVersionKind, conver
 	return nil
 }
 
-// AddStructFieldConversion allows you to specify a mechanical copy for a moved
-// or renamed struct field without writing an entire conversion function. See
-// the comment in conversion.Converter.SetStructFieldCopy for parameter details.
-// Call as many times as needed, even on the same fields.
-func (s *Scheme) AddStructFieldConversion(srcFieldType interface{}, srcFieldName string, destFieldType interface{}, destFieldName string) error {
-	return s.converter.SetStructFieldCopy(srcFieldType, srcFieldName, destFieldType, destFieldName)
-}
-
 // RegisterInputDefaults sets the provided field mapping function and field matching
 // as the defaults for the provided input type.  The fn may be nil, in which case no
 // mapping will happen by default. Use this method to register a mechanism for handling