go/types, types2: remove under(Type) in favor of Type.Underlying()

As of CL 695977, under(Type) simply delegates to Type.Underlying().
This is just a cleanup.

Change-Id: I48d5fddc38560dfe485184faa6a5ff713bea74a0
Reviewed-on: https://go-review.googlesource.com/c/go/+/712400
Commit-Queue: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: Mark Freeman

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

@@ -91,7 +91,7 @@ func (check *Checker) assignment(x *operand, T Type, context string) {
 	// x.typ is typed
 
 	// A generic (non-instantiated) function value cannot be assigned to a variable.
-	if sig, _ := under(x.typ).(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
+	if sig, _ := x.typ.Underlying().(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
 		check.errorf(x, WrongTypeArgCount, "cannot use generic function %s without instantiation in %s", x, context)
 		x.mode = invalid
 		return
@@ -261,7 +261,7 @@ func (check *Checker) assignVar(lhs, rhs syntax.Expr, x *operand, context string
 		var target *target
 		// avoid calling ExprString if not needed
 		if T != nil {
-			if _, ok := under(T).(*Signature); ok {
+			if _, ok := T.Underlying().(*Signature); ok {
 				target = newTarget(T, ExprString(lhs))
 			}
 		}

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

@@ -144,7 +144,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		// len(x)
 		mode := invalid
 		var val constant.Value
-		switch t := arrayPtrDeref(under(x.typ)).(type) {
+		switch t := arrayPtrDeref(x.typ.Underlying()).(type) {
 		case *Basic:
 			if isString(t) && id == _Len {
 				if x.mode == constant_ {
@@ -203,7 +203,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 		if mode == invalid {
 			// avoid error if underlying type is invalid
-			if isValid(under(x.typ)) {
+			if isValid(x.typ.Underlying()) {
 				code := InvalidCap
 				if id == _Len {
 					code = InvalidLen
@@ -322,7 +322,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		// (applyTypeFunc never calls f with a type parameter)
 		f := func(typ Type) Type {
 			assert(!isTypeParam(typ))
-			if t, _ := under(typ).(*Basic); t != nil {
+			if t, _ := typ.Underlying().(*Basic); t != nil {
 				switch t.kind {
 				case Float32:
 					return Typ[Complex64]
@@ -472,7 +472,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 		// (applyTypeFunc never calls f with a type parameter)
 		f := func(typ Type) Type {
 			assert(!isTypeParam(typ))
-			if t, _ := under(typ).(*Basic); t != nil {
+			if t, _ := typ.Underlying().(*Basic); t != nil {
 				switch t.kind {
 				case Complex64:
 					return Typ[Float32]
@@ -1020,7 +1020,7 @@ func hasVarSize(t Type, seen map[*Named]bool) (varSized bool) {
 		}()
 	}
 
-	switch u := under(t).(type) {
+	switch u := t.Underlying().(type) {
 	case *Array:
 		return hasVarSize(u.elem, seen)
 	case *Struct:
@@ -1112,7 +1112,7 @@ func makeSig(res Type, args ...Type) *Signature {
 // otherwise it returns typ.
 func arrayPtrDeref(typ Type) Type {
 	if p, ok := Unalias(typ).(*Pointer); ok {
-		if a, _ := under(p.base).(*Array); a != nil {
+		if a, _ := p.base.Underlying().(*Array); a != nil {
 			return a
 		}
 	}

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

@@ -205,7 +205,7 @@ func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
 		case 1:
 			check.expr(nil, x, call.ArgList[0])
 			if x.mode != invalid {
-				if t, _ := under(T).(*Interface); t != nil && !isTypeParam(T) {
+				if t, _ := T.Underlying().(*Interface); t != nil && !isTypeParam(T) {
 					if !t.IsMethodSet() {
 						check.errorf(call, MisplacedConstraintIface, "cannot use interface %s in conversion (contains specific type constraints or is comparable)", T)
 						break
@@ -812,7 +812,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr, def *TypeName
 	obj, index, indirect = lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel, false)
 	if obj == nil {
 		// Don't report another error if the underlying type was invalid (go.dev/issue/49541).
-		if !isValid(under(x.typ)) {
+		if !isValid(x.typ.Underlying()) {
 			goto Error
 		}
 

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

@@ -33,7 +33,7 @@ func (check *Checker) overflow(x *operand, opPos syntax.Pos) {
 	// x.typ cannot be a type parameter (type
 	// parameters cannot be constant types).
 	if isTyped(x.typ) {
-		check.representable(x, under(x.typ).(*Basic))
+		check.representable(x, x.typ.Underlying().(*Basic))
 		return
 	}
 

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

@@ -18,7 +18,7 @@ func (check *Checker) conversion(x *operand, T Type) {
 	constArg := x.mode == constant_
 
 	constConvertibleTo := func(T Type, val *constant.Value) bool {
-		switch t, _ := under(T).(*Basic); {
+		switch t, _ := T.Underlying().(*Basic); {
 		case t == nil:
 			// nothing to do
 		case representableConst(x.val, check, t, val):
@@ -142,8 +142,8 @@ func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
 	origT := T
 	V := Unalias(x.typ)
 	T = Unalias(T)
-	Vu := under(V)
-	Tu := under(T)
+	Vu := V.Underlying()
+	Tu := T.Underlying()
 	Vp, _ := V.(*TypeParam)
 	Tp, _ := T.(*TypeParam)
 
@@ -158,7 +158,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
 	// and their pointer base types are not type parameters"
 	if V, ok := V.(*Pointer); ok {
 		if T, ok := T.(*Pointer); ok {
-			if IdenticalIgnoreTags(under(V.base), under(T.base)) && !isTypeParam(V.base) && !isTypeParam(T.base) {
+			if IdenticalIgnoreTags(V.base.Underlying(), T.base.Underlying()) && !isTypeParam(V.base) && !isTypeParam(T.base) {
 				return true
 			}
 		}
@@ -211,7 +211,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
 				return false
 			}
 		case *Pointer:
-			if a, _ := under(a.Elem()).(*Array); a != nil {
+			if a, _ := a.Elem().Underlying().(*Array); a != nil {
 				if Identical(s.Elem(), a.Elem()) {
 					if check == nil || check.allowVersion(go1_17) {
 						return true
@@ -292,23 +292,23 @@ func (x *operand) convertibleTo(check *Checker, T Type, cause *string) bool {
 }
 
 func isUintptr(typ Type) bool {
-	t, _ := under(typ).(*Basic)
+	t, _ := typ.Underlying().(*Basic)
 	return t != nil && t.kind == Uintptr
 }
 
 func isUnsafePointer(typ Type) bool {
-	t, _ := under(typ).(*Basic)
+	t, _ := typ.Underlying().(*Basic)
 	return t != nil && t.kind == UnsafePointer
 }
 
 func isPointer(typ Type) bool {
-	_, ok := under(typ).(*Pointer)
+	_, ok := typ.Underlying().(*Pointer)
 	return ok
 }
 
 func isBytesOrRunes(typ Type) bool {
-	if s, _ := under(typ).(*Slice); s != nil {
-		t, _ := under(s.elem).(*Basic)
+	if s, _ := typ.Underlying().(*Slice); s != nil {
+		t, _ := s.elem.Underlying().(*Basic)
 		return t != nil && (t.kind == Byte || t.kind == Rune)
 	}
 	return false

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

@@ -391,7 +391,7 @@ func (check *Checker) constDecl(obj *Const, typ, init syntax.Expr, inherited boo
 		if !isConstType(t) {
 			// don't report an error if the type is an invalid C (defined) type
 			// (go.dev/issue/22090)
-			if isValid(under(t)) {
+			if isValid(t.Underlying()) {
 				check.errorf(typ, InvalidConstType, "invalid constant type %s", t)
 			}
 			obj.typ = Typ[Invalid]

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

@@ -361,7 +361,7 @@ func (check *Checker) updateExprType(x syntax.Expr, typ Type, final bool) {
 	// If the new type is not final and still untyped, just
 	// update the recorded type.
 	if !final && isUntyped(typ) {
-		old.typ = under(typ).(*Basic)
+		old.typ = typ.Underlying().(*Basic)
 		check.untyped[x] = old
 		return
 	}
@@ -431,7 +431,7 @@ func (check *Checker) implicitTypeAndValue(x *operand, target Type) (Type, const
 		return nil, nil, InvalidUntypedConversion
 	}
 
-	switch u := under(target).(type) {
+	switch u := target.Underlying().(type) {
 	case *Basic:
 		if x.mode == constant_ {
 			v, code := check.representation(x, u)
@@ -616,7 +616,7 @@ Error:
 // incomparableCause returns a more specific cause why typ is not comparable.
 // If there is no more specific cause, the result is "".
 func (check *Checker) incomparableCause(typ Type) string {
-	switch under(typ).(type) {
+	switch typ.Underlying().(type) {
 	case *Slice, *Signature, *Map:
 		return compositeKind(typ) + " can only be compared to nil"
 	}
@@ -963,7 +963,7 @@ type target struct {
 // The result is nil if typ is not a signature.
 func newTarget(typ Type, desc string) *target {
 	if typ != nil {
-		if sig, _ := under(typ).(*Signature); sig != nil {
+		if sig, _ := typ.Underlying().(*Signature); sig != nil {
 			return &target{sig, desc}
 		}
 	}
@@ -1112,7 +1112,7 @@ func (check *Checker) exprInternal(T *target, x *operand, e syntax.Expr, hint Ty
 			check.errorf(x, InvalidAssert, invalidOp+"cannot use type assertion on type parameter value %s", x)
 			goto Error
 		}
-		if _, ok := under(x.typ).(*Interface); !ok {
+		if _, ok := x.typ.Underlying().(*Interface); !ok {
 			check.errorf(x, InvalidAssert, invalidOp+"%s is not an interface", x)
 			goto Error
 		}

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

@@ -16,7 +16,7 @@ func (s *gcSizes) Alignof(T Type) (result int64) {
 
 	// For arrays and structs, alignment is defined in terms
 	// of alignment of the elements and fields, respectively.
-	switch t := under(T).(type) {
+	switch t := T.Underlying().(type) {
 	case *Array:
 		// spec: "For a variable x of array type: unsafe.Alignof(x)
 		// is the same as unsafe.Alignof(x[0]), but at least 1."
@@ -96,7 +96,7 @@ func (s *gcSizes) Offsetsof(fields []*Var) []int64 {
 }
 
 func (s *gcSizes) Sizeof(T Type) int64 {
-	switch t := under(T).(type) {
+	switch t := T.Underlying().(type) {
 	case *Basic:
 		assert(isTyped(T))
 		k := t.kind

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

@@ -35,7 +35,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 		return false
 
 	case value:
-		if sig, _ := under(x.typ).(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
+		if sig, _ := x.typ.Underlying().(*Signature); sig != nil && sig.TypeParams().Len() > 0 {
 			// function instantiation
 			return true
 		}
@@ -50,7 +50,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 	// ordinary index expression
 	valid := false
 	length := int64(-1) // valid if >= 0
-	switch typ := under(x.typ).(type) {
+	switch typ := x.typ.Underlying().(type) {
 	case *Basic:
 		if isString(typ) {
 			valid = true
@@ -73,7 +73,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 		x.typ = typ.elem
 
 	case *Pointer:
-		if typ, _ := under(typ.base).(*Array); typ != nil {
+		if typ, _ := typ.base.Underlying().(*Array); typ != nil {
 			valid = true
 			length = typ.len
 			x.mode = variable
@@ -124,7 +124,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst boo
 					mode = value
 				}
 			case *Pointer:
-				if t, _ := under(t.base).(*Array); t != nil {
+				if t, _ := t.base.Underlying().(*Array); t != nil {
 					l = t.len
 					e = t.elem
 				}
@@ -247,7 +247,7 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
 		// but don't go from untyped string to string.
 		cu = Typ[String]
 		if !isTypeParam(x.typ) {
-			cu = under(x.typ) // untyped string remains untyped
+			cu = x.typ.Underlying() // untyped string remains untyped
 		}
 	}
 
@@ -292,7 +292,7 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
 		x.typ = &Slice{elem: u.elem}
 
 	case *Pointer:
-		if u, _ := under(u.base).(*Array); u != nil {
+		if u, _ := u.base.Underlying().(*Array); u != nil {
 			valid = true
 			length = u.len
 			x.typ = &Slice{elem: u.elem}

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

@@ -668,7 +668,7 @@ func coreTerm(tpar *TypeParam) (*term, bool) {
 	if n == 1 {
 		if debug {
 			u, _ := commonUnder(tpar, nil)
-			assert(under(single.typ) == u)
+			assert(single.typ.Underlying() == u)
 		}
 		return single, true
 	}