cmd/cue: use fewer go/types.Type.String calls

Reimplement the same logic without roundtrips to the String method,
which makes our logic more precise and less error prone,
and also avoids the relatively expensive String call with its buffer
and printer allocations and added complexity.

More String method calls remain; these were the lowest hanging fruit.
Also tweak the TODO about []byte and []uint8.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ifedcf04f1c492b69b23760f5b8e8858fe3cd99bc
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1185034
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

Author: mvdan

cmd/cue/cmd/get_go.go

@@ -281,9 +281,11 @@ func (e *extractor) usedPkg(pkg string) {
 }
 
 var (
-	typeAny   = types.NewInterfaceType(nil, nil).Complete() // interface{}
-	typeBytes = types.NewSlice(types.Typ[types.Byte])       // []byte
-	typeError = types.Universe.Lookup("error").Type()       // error
+	typeAny    = types.Universe.Lookup("any").Type()    // any or interface{}
+	typeByte   = types.Universe.Lookup("byte").Type()   // byte
+	typeBytes  = types.NewSlice(typeByte)               // []byte
+	typeString = types.Universe.Lookup("string").Type() // string
+	typeError  = types.Universe.Lookup("error").Type()  // error
 )
 
 // Note that we can leave positions, packages, and parameter/result names empty.
@@ -804,12 +806,13 @@ func (e *extractor) reportDecl(x *ast.GenDecl) (a []cueast.Decl) {
 				}
 
 				typ := e.pkg.TypesInfo.TypeOf(name)
-				if s := typ.String(); !strings.Contains(s, "untyped") {
-					switch s {
-					case "byte", "string", "error":
-					default:
-						cv = cueast.NewBinExpr(cuetoken.AND, e.makeType(typ), cv)
+				switch typ {
+				case typeByte, typeString, typeError:
+				default:
+					if basic, ok := typ.(*types.Basic); ok && basic.Info()&types.IsUntyped != 0 {
+						break // untyped basic types do not make valid identifiers
 					}
+					cv = cueast.NewBinExpr(cuetoken.AND, e.makeType(typ), cv)
 				}
 
 				f.Value = cv
@@ -963,7 +966,7 @@ func supportedType(stack []types.Type, t types.Type) (ok bool) {
 	t = t.Underlying()
 	switch x := t.(type) {
 	case *types.Basic:
-		return x.String() != "invalid type"
+		return x.Kind() != types.Invalid
 	case *types.Named:
 		return true
 	case *types.Pointer:
@@ -1042,9 +1045,8 @@ func (e *extractor) makeType(expr types.Type) (result cueast.Expr) {
 			return e.ident("_", false)
 		}
 		// Check for builtin packages.
-		// TODO: replace these literal types with a reference to the fixed
-		switch obj.Type().String() {
-		case "time.Time":
+		switch {
+		case obj.Pkg().Path() == "time" && obj.Name() == "Time":
 			ref := e.ident(e.pkgNames[obj.Pkg().Path()].name, false)
 			var name *cueast.Ident
 			if ref.Name != "time" {
@@ -1053,7 +1055,7 @@ func (e *extractor) makeType(expr types.Type) (result cueast.Expr) {
 			ref.Node = cueast.NewImport(name, "time")
 			return cueast.NewSel(ref, obj.Name())
 
-		case "math/big.Int":
+		case obj.Pkg().Path() == "math/big" && obj.Name() == "Int":
 			return e.ident("int", false)
 
 		default:
@@ -1151,16 +1153,18 @@ func (e *extractor) makeType(expr types.Type) (result cueast.Expr) {
 		return st
 
 	case *types.Slice:
-		// TODO: should this be x.Elem().Underlying().String()? One could
-		// argue either way.
-		if x.Elem().String() == "byte" {
+		// Note that []byte is treated different from []uint8,
+		// even though byte is an alias for the basic type uint8.
+		// TODO: reconsider this; both encoding/json and the future v2
+		// encode []uint8, or anything assignable to []byte, as bytes.
+		if x.Elem() == typeByte {
 			return e.ident("bytes", false)
 		}
 		return cueast.NewList(&cueast.Ellipsis{Type: e.makeType(x.Elem())})
 
 	case *types.Array:
-		if x.Elem().String() == "byte" {
-			// TODO: no way to constraint lengths of bytes for now, as regexps
+		if x.Elem() == typeByte {
+			// TODO: no way to constrain lengths of bytes for now, as regexps
 			// operate on Unicode, not bytes. So we need
 			//     fmt.Fprint(e.w, fmt.Sprintf("=~ '^\C{%d}$'", x.Len())),
 			// but regexp does not support that.
@@ -1202,7 +1206,7 @@ func (e *extractor) makeType(expr types.Type) (result cueast.Expr) {
 		case types.Complex64, types.Complex128:
 			return e.ident("_", false)
 		}
-		return e.ident(x.String(), false)
+		return e.ident(x.Name(), false)
 
 	case *types.Union:
 		var exprs []cueast.Expr