internal/filetypes: simplify some of the CUE logic

hasEncoding returned both whether the encoding field was concrete
and whether the field had a concrete default value,
when in fact only the latter was necessary - no tests change behavior
with this change, even though a couple of unit tests did run into
the edge case of hasEncoding returning (false, true).

The change to have hasEncoding return two values is relatively recent,
from https://cue-review.googlesource.com/c/cue/+/5410 in mid 2020,
and it seems like none of the added test cases there needed the added
logic to hasEncoding.

While here, move "tags" back to the top-level scope.
Just like the "interpretations" struct, it does not vary between modes.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I7d238617f249bced74d0e5ee640e92e86e5d4dda
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1193575
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

internal/filetypes/filetypes.go

@@ -259,31 +259,26 @@ func ParseFile(s string, mode Mode) (*build.File, error) {
 	return toFile(modeVal, fileVal, file)
 }
 
-func hasEncoding(v cue.Value) (concrete, hasDefault bool) {
+func hasEncoding(v cue.Value) bool {
 	enc := v.LookupPath(cue.MakePath(cue.Str("encoding")))
 	d, _ := enc.Default()
-	return enc.IsConcrete(), d.IsConcrete()
+	return d.IsConcrete()
 }
 
 func toFile(modeVal, fileVal cue.Value, filename string) (*build.File, error) {
 	fileVal = fileVal.Fill(filename, "filename")
 
-	if concrete, hasDefault := hasEncoding(fileVal); !concrete {
+	if !hasEncoding(fileVal) {
 		if filename == "-" {
-			if !hasDefault {
-				fileVal = fileVal.Unify(modeVal.LookupPath(cue.MakePath(cue.Str("Default"))))
-			}
+			fileVal = fileVal.Unify(modeVal.LookupPath(cue.MakePath(cue.Str("Default"))))
 		} else if ext := fileExt(filename); ext != "" {
-			if x := modeVal.LookupPath(cue.MakePath(cue.Str("extensions"), cue.Str(ext))); x.Exists() || !hasDefault {
-				fileVal = fileVal.Unify(x)
-				if err := fileVal.Err(); err != nil {
-					return nil, errors.Newf(token.NoPos,
-						"unknown file extension %s", ext)
-				}
+			extFile := modeVal.LookupPath(cue.MakePath(cue.Str("extensions"), cue.Str(ext)))
+			fileVal = fileVal.Unify(extFile)
+			if err := fileVal.Err(); err != nil {
+				return nil, errors.Newf(token.NoPos, "unknown file extension %s", ext)
 			}
-		} else if !hasDefault {
-			return nil, errors.Newf(token.NoPos,
-				"no encoding specified for file %q", filename)
+		} else {
+			return nil, errors.Newf(token.NoPos, "no encoding specified for file %q", filename)
 		}
 	}
 
@@ -295,19 +290,19 @@ func toFile(modeVal, fileVal cue.Value, filename string) (*build.File, error) {
 	return f, nil
 }
 
-func parseType(s string, mode Mode) (modeVal, fileVal cue.Value, _ error) {
+func parseType(scope string, mode Mode) (modeVal, fileVal cue.Value, _ error) {
 	modeVal = typesValue.LookupPath(cue.MakePath(cue.Str("modes"), cue.Str(mode.String())))
 	fileVal = modeVal.LookupPath(cue.MakePath(cue.Str("File")))
 
-	if s != "" {
-		for _, t := range strings.Split(s, "+") {
-			if p := strings.IndexByte(t, '='); p >= 0 {
-				fileVal = fileVal.Fill(t[p+1:], "tags", t[:p])
+	if scope != "" {
+		for _, tag := range strings.Split(scope, "+") {
+			tagName, tagVal, ok := strings.Cut(tag, "=")
+			if ok {
+				fileVal = fileVal.Fill(tagVal, "tags", tagName)
 			} else {
-				info := modeVal.LookupPath(cue.MakePath(cue.Str("tags"), cue.Str(t)))
+				info := typesValue.LookupPath(cue.MakePath(cue.Str("tags"), cue.Str(tag)))
 				if !info.Exists() {
-					return cue.Value{}, cue.Value{}, errors.Newf(token.NoPos,
-						"unknown filetype %s", t)
+					return cue.Value{}, cue.Value{}, errors.Newf(token.NoPos, "unknown filetype %s", tag)
 				}
 				fileVal = fileVal.Unify(info)
 			}

internal/filetypes/types.cue

@@ -168,63 +168,6 @@ modes: [string]: {
 		// ".pb":        tags.binpb // binarypb
 	}
 
-	// tags maps command line tags to file properties.
-	tags: {
-		schema: form: "schema"
-		graph: form:  "graph"
-		dag: form:    "dag"
-		data: form:   "data"
-
-		cue: encoding: "cue"
-
-		json: encoding:      "json"
-		jsonl: encoding:     "jsonl"
-		yaml: encoding:      "yaml"
-		proto: encoding:     "proto"
-		textproto: encoding: "textproto"
-		// "binpb":  encodings.binproto
-
-		// pb is used either to indicate binary encoding, or to indicate
-		pb: *{
-			encoding:       "binarypb"
-			interpretation: ""
-		} | {
-			encoding:       !="binarypb"
-			interpretation: "pb"
-		}
-
-		text: {
-			encoding: "text"
-			form:     "data"
-		}
-		binary: {
-			encoding: "binary"
-			form:     "data"
-		}
-		go: {
-			encoding:       "code"
-			interpretation: ""
-			tags: lang: "go"
-		}
-		code: {
-			encoding:       "code"
-			interpretation: ""
-			tags: lang: *"" | string
-		}
-
-		auto: {
-			interpretation: "auto"
-			encoding:       *"json" | _
-		}
-		jsonschema: {
-			interpretation: "jsonschema"
-			encoding:       *"json" | _
-		}
-		openapi: {
-			interpretation: "openapi"
-			encoding:       *"json" | _
-		}
-	}
 	// encodings: "": error("no encoding specified")
 
 	encodings: cue: {
@@ -365,3 +308,61 @@ interpretations: pb: {
 	forms.data
 	stream: true
 }
+
+// tags maps command line tags to file properties.
+tags: {
+	schema: form: "schema"
+	graph: form:  "graph"
+	dag: form:    "dag"
+	data: form:   "data"
+
+	cue: encoding: "cue"
+
+	json: encoding:      "json"
+	jsonl: encoding:     "jsonl"
+	yaml: encoding:      "yaml"
+	proto: encoding:     "proto"
+	textproto: encoding: "textproto"
+	// "binpb":  encodings.binproto
+
+	// pb is used either to indicate binary encoding, or to indicate
+	pb: *{
+		encoding:       "binarypb"
+		interpretation: ""
+	} | {
+		encoding:       !="binarypb"
+		interpretation: "pb"
+	}
+
+	text: {
+		encoding: "text"
+		form:     "data"
+	}
+	binary: {
+		encoding: "binary"
+		form:     "data"
+	}
+	go: {
+		encoding:       "code"
+		interpretation: ""
+		tags: lang: "go"
+	}
+	code: {
+		encoding:       "code"
+		interpretation: ""
+		tags: lang: *"" | string
+	}
+
+	auto: {
+		interpretation: "auto"
+		encoding:       *"json" | _
+	}
+	jsonschema: {
+		interpretation: "jsonschema"
+		encoding:       *"json" | _
+	}
+	openapi: {
+		interpretation: "openapi"
+		encoding:       *"json" | _
+	}
+}