go/types: generate conversions.go from types2 source

This CL reduces the amount of code that needs to be maintained
manually by about 300 LOC.

Change-Id: I749e47668e90e77e99109005fbe19045d4a5ad29
Reviewed-on: https://go-review.googlesource.com/c/go/+/565437
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>

src/cmd/compile/internal/types2/conversions.go

@@ -98,17 +98,18 @@ func (check *Checker) conversion(x *operand, T Type) {
 	// given a type explicitly by a constant declaration or conversion,...".
 	if isUntyped(x.typ) {
 		final := T
-		// - For conversions to interfaces, except for untyped nil arguments,
-		//   use the argument's default type.
+		// - For conversions to interfaces, except for untyped nil arguments
+		//   and isTypes2, use the argument's default type.
 		// - For conversions of untyped constants to non-constant types, also
 		//   use the default type (e.g., []byte("foo") should report string
 		//   not []byte as type for the constant "foo").
+		// - If !isTypes2, keep untyped nil for untyped nil arguments.
 		// - For constant integer to string conversions, keep the argument type.
 		//   (See also the TODO below.)
-		if x.typ == Typ[UntypedNil] {
+		if isTypes2 && x.typ == Typ[UntypedNil] {
 			// ok
-		} else if isNonTypeParamInterface(T) || constArg && !isConstType(T) {
-			final = Default(x.typ)
+		} else if isNonTypeParamInterface(T) || constArg && !isConstType(T) || !isTypes2 && x.isNil() {
+			final = Default(x.typ) // default type of untyped nil is untyped nil
 		} else if x.mode == constant_ && isInteger(x.typ) && allString(T) {
 			final = x.typ
 		}
@@ -227,7 +228,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
 		return false
 	}
 
-	errorf := func(format string, args ...interface{}) {
+	errorf := func(format string, args ...any) {
 		if check != nil && cause != nil {
 			msg := check.sprintf(format, args...)
 			if *cause != "" {

src/cmd/compile/internal/types2/util.go

@@ -11,6 +11,8 @@ package types2
 
 import "cmd/compile/internal/syntax"
 
+const isTypes2 = true
+
 // cmpPos compares the positions p and q and returns a result r as follows:
 //
 // r <  0: p is before q

src/go/types/conversions.go

@@ -1,3 +1,5 @@
+// Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
+
 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
@@ -98,14 +100,17 @@ func (check *Checker) conversion(x *operand, T Type) {
 	// given a type explicitly by a constant declaration or conversion,...".
 	if isUntyped(x.typ) {
 		final := T
-		// - For conversions to interfaces, use the argument's default type.
+		// - For conversions to interfaces, except for untyped nil arguments
+		//   and isTypes2, use the argument's default type.
 		// - For conversions of untyped constants to non-constant types, also
 		//   use the default type (e.g., []byte("foo") should report string
 		//   not []byte as type for the constant "foo").
-		// - Keep untyped nil for untyped nil arguments.
+		// - If !isTypes2, keep untyped nil for untyped nil arguments.
 		// - For constant integer to string conversions, keep the argument type.
 		//   (See also the TODO below.)
-		if isNonTypeParamInterface(T) || constArg && !isConstType(T) || x.isNil() {
+		if isTypes2 && x.typ == Typ[UntypedNil] {
+			// ok
+		} else if isNonTypeParamInterface(T) || constArg && !isConstType(T) || !isTypes2 && x.isNil() {
 			final = Default(x.typ) // default type of untyped nil is untyped nil
 		} else if x.mode == constant_ && isInteger(x.typ) && allString(T) {
 			final = x.typ

src/go/types/generate_test.go

@@ -115,6 +115,7 @@ var filemap = map[string]action{
 	"const.go":        func(f *ast.File) { fixTokenPos(f) },
 	"context.go":      nil,
 	"context_test.go": nil,
+	"conversions.go":  nil,
 	"errsupport.go":   nil,
 	"gccgosizes.go":   nil,
 	"gcsizes.go":      func(f *ast.File) { renameIdents(f, "IsSyncAtomicAlign64->_IsSyncAtomicAlign64") },

src/go/types/util.go

@@ -14,6 +14,8 @@ import (
 	"go/token"
 )
 
+const isTypes2 = false
+
 // cmpPos compares the positions p and q and returns a result r as follows:
 //
 // r <  0: p is before q