cmd/compile: handle any as alias like byte and rune

`types.Types[types.TINTER]` is already used for `interface{}`, so we
can conveniently just extend the existing logic that substitutes
`byte` and `rune` with `uint8` and `int32` to also substitute `any`.

Fixes #49665.

Change-Id: I1ab1954699934150aab899b35037d5611c8ca47e
Reviewed-on: https://go-review.googlesource.com/c/go/+/365354
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/cmd/compile/internal/reflectdata/reflect.go

@@ -924,11 +924,12 @@ func hashMightPanic(t *types.Type) bool {
 	}
 }
 
-// formalType replaces byte and rune aliases with real types.
+// formalType replaces predeclared aliases with real types.
 // They've been separate internally to make error messages
 // better, but we have to merge them in the reflect tables.
 func formalType(t *types.Type) *types.Type {
-	if t == types.ByteType || t == types.RuneType {
+	switch t {
+	case types.AnyType, types.ByteType, types.RuneType:
 		return types.Types[t.Kind()]
 	}
 	return t

src/cmd/compile/internal/types/fmt.go

@@ -328,8 +328,8 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 		return
 	}
 
-	if t == ByteType || t == RuneType {
-		// in %-T mode collapse rune and byte with their originals.
+	if t == AnyType || t == ByteType || t == RuneType {
+		// in %-T mode collapse predeclared aliases with their originals.
 		switch mode {
 		case fmtTypeIDName, fmtTypeID:
 			t = Types[t.Kind()]

src/cmd/compile/internal/types/identity.go

@@ -58,6 +58,8 @@ func identical(t1, t2 *Type, flags int, assumedEqual map[typePair]struct{}) bool
 			return (t1 == Types[TUINT8] || t1 == ByteType) && (t2 == Types[TUINT8] || t2 == ByteType)
 		case TINT32:
 			return (t1 == Types[TINT32] || t1 == RuneType) && (t2 == Types[TINT32] || t2 == RuneType)
+		case TINTER:
+			return (t1 == Types[TINTER] || t1 == AnyType) && (t2 == Types[TINTER] || t2 == AnyType)
 		default:
 			return false
 		}

src/cmd/compile/internal/types/type.go

@@ -106,12 +106,16 @@ const (
 // It also stores pointers to several special types:
 //   - Types[TANY] is the placeholder "any" type recognized by SubstArgTypes.
 //   - Types[TBLANK] represents the blank variable's type.
+//   - Types[TINTER] is the canonical "interface{}" type.
 //   - Types[TNIL] represents the predeclared "nil" value's type.
 //   - Types[TUNSAFEPTR] is package unsafe's Pointer type.
 var Types [NTYPE]*Type
 
 var (
-	// Predeclared alias types. Kept separate for better error messages.
+	// Predeclared alias types. These are actually created as distinct
+	// defined types for better error messages, but are then specially
+	// treated as identical to their respective underlying types.
+	AnyType  *Type
 	ByteType *Type
 	RuneType *Type
 
@@ -119,8 +123,6 @@ var (
 	ErrorType *Type
 	// Predeclared comparable interface type.
 	ComparableType *Type
-	// Predeclared any interface type.
-	AnyType *Type
 
 	// Types to represent untyped string and boolean constants.
 	UntypedString = newType(TSTRING)
@@ -1207,6 +1209,11 @@ func (t *Type) cmp(x *Type) Cmp {
 			if (t == Types[RuneType.kind] || t == RuneType) && (x == Types[RuneType.kind] || x == RuneType) {
 				return CMPeq
 			}
+
+		case TINTER:
+			if (t == Types[AnyType.kind] || t == AnyType) && (x == Types[AnyType.kind] || x == AnyType) {
+				return CMPeq
+			}
 		}
 	}
 

src/cmd/compile/internal/types/universe.go

@@ -59,6 +59,7 @@ func InitTypes(defTypeName func(sym *Sym, typ *Type) Object) {
 
 	Types[TANY] = newType(TANY)
 	Types[TINTER] = NewInterface(LocalPkg, nil, false)
+	CheckSize(Types[TINTER])
 
 	defBasic := func(kind Kind, pkg *Pkg, name string) *Type {
 		typ := newType(kind)
@@ -108,11 +109,14 @@ func InitTypes(defTypeName func(sym *Sym, typ *Type) Object) {
 	ResumeCheckSize()
 
 	// any type (interface)
-	if base.Flag.G > 0 {
 	DeferCheckSize()
 	AnyType = defBasic(TFORW, BuiltinPkg, "any")
 	AnyType.SetUnderlying(NewInterface(NoPkg, []*Field{}, false))
 	ResumeCheckSize()
+
+	if base.Flag.G == 0 {
+		ComparableType.Sym().Def = nil
+		AnyType.Sym().Def = nil
 	}
 
 	Types[TUNSAFEPTR] = defBasic(TUNSAFEPTR, UnsafePkg, "Pointer")

test/fixedbugs/issue49665.go

@@ -0,0 +1,18 @@
+// run
+
+// Copyright 2021 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.
+
+package main
+
+import "fmt"
+
+var x any
+var y interface{}
+
+var _ = &x == &y // assert x and y have identical types
+
+func main() {
+	fmt.Printf("%T\n%T\n", &x, &y)
+}

test/fixedbugs/issue49665.out

@@ -0,0 +1,2 @@
+*interface {}
+*interface {}