internal/filetypes: speed up common case

Creating a `*build.File` value is somewhat expensive in the general
case, but the general case is fairly unusual: it's much more common to
have files interpreted according to their extension only with defaults
for all other encoding attributes.

Make this operation more efficient (no CUE value lookup required) for
this common case by caching the resulting `*build.File` values for each
of the known file extensions at init time.

While we're about it, change the existing "common case" logic to use a
check that matches the actual invariants of the common case for CUE:
specifically the default encoding for CUE uses `form: ""` not `form:
"schema"`: this makes a difference in subsequent CLs in the checks for
whether a given parsed CUE file can be cached.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I46f8c823cca08a44a09dece8d5e9a3df55bcf928
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197557
Reviewed-by: Paul Jolly <paul@myitcv.io>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

internal/filetypes/filetypes.go

@@ -78,7 +78,7 @@ func FromFile(b *build.File, mode Mode) (*FileInfo, error) {
 	// isolation without interference from evaluating these files.
 	if mode == Input &&
 		b.Encoding == build.CUE &&
-		b.Form == build.Schema &&
+		b.Form == "" &&
 		b.Interpretation == "" {
 		return &FileInfo{
 			File: b,
@@ -175,11 +175,9 @@ func ParseArgs(args []string) (files []*build.File, err error) {
 			if !fileVal.Exists() {
 				if len(a) == 1 && strings.HasSuffix(a[0], ".cue") {
 					// Handle majority case.
-					files = append(files, &build.File{
-						Filename: a[0],
-						Encoding: build.CUE,
-						Form:     build.Schema,
-					})
+					f := *fileForCUE
+					f.Filename = a[0]
+					files = append(files, &f)
 					hasFiles = true
 					continue
 				}
@@ -269,15 +267,20 @@ func ParseFileAndType(file, scope string, mode Mode) (*build.File, error) {
 	// Quickly discard files which we aren't interested in.
 	// These cases are very common when loading `./...` in a large repository.
 	typesInit()
-	if scope == "" {
+	if scope == "" && file != "-" {
 		ext := fileExt(file)
-		if file == "-" {
-			// not handled here
-		} else if ext == "" {
+		if ext == "" {
 			return nil, errors.Newf(token.NoPos, "no encoding specified for file %q", file)
-		} else if !knownExtensions[ext] {
+		}
+		f, ok := fileForExt[ext]
+		if !ok {
 			return nil, errors.Newf(token.NoPos, "unknown file extension %s", ext)
 		}
+		if mode == Input {
+			f1 := *f
+			f1.Filename = file
+			return &f1, nil
+		}
 	}
 	modeVal, fileVal, err := parseType(scope, mode)
 	if err != nil {

internal/filetypes/types.cue

@@ -3,7 +3,7 @@
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
-// 
+//
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
@@ -56,15 +56,15 @@ package build
 	attributes?:   bool          // include/allow attributes
 }
 
-// knownExtensions derives all the known file extensions
-// from those that are mentioned in modes,
-// allowing us to quickly discard files with unknown extensions.
-knownExtensions: {
-	for mode in modes
-	for ext, _ in mode.extensions {
-		(ext): true
-	}
-}
+// fileForExtVanilla holds the extensions supported in
+// input mode with scope="" - the most common form
+// of file type to evaluate.
+//
+// It's also used as a source of truth for all known file
+// extensions as all modes define attributes for
+// all file extensions. If that ever changed, we'd need
+// to change this.
+fileForExtVanilla: modes.input.extensions
 
 // modes sets defaults for different operational modes.
 modes: [string]: {

internal/filetypes/types.go

@@ -16,25 +16,38 @@ package filetypes
 
 import (
 	_ "embed"
+	"fmt"
 	"sync"
 
 	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/build"
 	"cuelang.org/go/cue/cuecontext"
 )
 
 //go:embed types.cue
 var typesCUE string
 
-var typesValue cue.Value
-var knownExtensions map[string]bool
+var (
+	typesValue cue.Value
+	fileForExt map[string]*build.File
+	fileForCUE *build.File
+)
 
 var typesInit = sync.OnceFunc(func() {
 	ctx := cuecontext.New()
 	typesValue = ctx.CompileString(typesCUE, cue.Filename("types.cue"))
 	if err := typesValue.Err(); err != nil {
 		panic(err)
 	}
-	if err := typesValue.LookupPath(cue.MakePath(cue.Str("knownExtensions"))).Decode(&knownExtensions); err != nil {
+	// Reading a file in input mode with a non-explicit scope is a very
+	// common operation, so cache the build.File value for all
+	// the known file extensions.
+	if err := typesValue.LookupPath(cue.MakePath(cue.Str("fileForExtVanilla"))).Decode(&fileForExt); err != nil {
 		panic(err)
 	}
+	fileForCUE = fileForExt[".cue"]
+	// Check invariants assumed by FromFile
+	if fileForCUE.Form != "" || fileForCUE.Interpretation != "" || fileForCUE.Encoding != build.CUE {
+		panic(fmt.Errorf("unexpected value for CUE file type: %#v", fileForCUE))
+	}
 })