go/packages: fix internal go list function signatures

After a discussion in cl/125535 this is a proposal to clean up some
internal function signatures that were becomming unwieldy.

Change-Id: I37a9e525ab18dface9ea9fb0b0ec68ac942ee632
Reviewed-on: https://go-review.googlesource.com/125659
Reviewed-by: Michael Matloob <matloob@golang.org>

go/packages/golist.go

@@ -8,7 +8,6 @@ package packages
 
 import (
 	"bytes"
-	"context"
 	"encoding/json"
 	"fmt"
 	"log"
@@ -31,7 +30,7 @@ type GoTooOldError struct {
 // golistPackages uses the "go list" command to expand the
 // pattern words and return metadata for the specified packages.
 // dir may be "" and env may be nil, as per os/exec.Command.
-func golistPackages(ctx context.Context, dir string, env []string, export, tests, deps bool, words []string) ([]*loaderPackage, error) {
+func golistPackages(cfg *rawConfig, words ...string) ([]*loaderPackage, error) {
 	// Fields must match go list;
 	// see $GOROOT/src/cmd/go/internal/load/pkg.go.
 	type jsonPackage struct {
@@ -53,7 +52,6 @@ func golistPackages(ctx context.Context, dir string, env []string, export, tests
 		ForTest      string // q in a "p [q.test]" package, else ""
 		DepOnly      bool
 	}
-
 	// go list uses the following identifiers in ImportPath and Imports:
 	//
 	// 	"p"			-- importable package or main (command)
@@ -68,7 +66,7 @@ func golistPackages(ctx context.Context, dir string, env []string, export, tests
 	// Run "go list" for complete
 	// information on the specified packages.
 
-	buf, err := golist(ctx, dir, env, export, tests, deps, words)
+	buf, err := golist(cfg, words)
 	if err != nil {
 		return nil, err
 	}
@@ -184,24 +182,15 @@ func absJoin(dir string, fileses ...[]string) (res []string) {
 }
 
 // golist returns the JSON-encoded result of a "go list args..." query.
-func golist(ctx context.Context, dir string, env []string, export, tests, deps bool, args []string) (*bytes.Buffer, error) {
+func golist(cfg *rawConfig, args []string) (*bytes.Buffer, error) {
 	out := new(bytes.Buffer)
-	cmd := exec.CommandContext(ctx, "go", append([]string{
-		"list",
-		"-e",
-		fmt.Sprintf("-cgo=%t", true),
-		fmt.Sprintf("-test=%t", tests),
-		fmt.Sprintf("-export=%t", export),
-		fmt.Sprintf("-deps=%t", deps),
-		"-json",
-		"--",
-	}, args...)...)
-
-	if env == nil {
-		env = os.Environ()
-	}
-	cmd.Env = env
-	cmd.Dir = dir
+	fullargs := []string{"list", "-e", "-json", "-cgo=true"}
+	fullargs = append(fullargs, cfg.Flags()...)
+	fullargs = append(fullargs, "--")
+	fullargs = append(fullargs, args...)
+	cmd := exec.CommandContext(cfg.Context, "go", fullargs...)
+	cmd.Env = cfg.Env
+	cmd.Dir = cfg.Dir
 	cmd.Stdout = out
 	cmd.Stderr = new(bytes.Buffer)
 	if err := cmd.Run(); err != nil {
@@ -222,7 +211,7 @@ func golist(ctx context.Context, dir string, env []string, export, tests, deps b
 		// If that build fails, errors appear on stderr
 		// (despite the -e flag) and the Export field is blank.
 		// Do not fail in that case.
-		if !export {
+		if !cfg.Export {
 			return nil, fmt.Errorf("go list: %s: %s", exitErr, cmd.Stderr)
 		}
 	}

go/packages/packages.go

@@ -266,9 +266,8 @@ func (ld *loader) load(patterns ...string) ([]*Package, error) {
 
 	// Do the metadata query and partial build.
 	// TODO(adonovan): support alternative build systems at this seam.
-	export := ld.Mode > LoadImports && ld.Mode < LoadAllSyntax
-	deps := ld.Mode >= LoadImports
-	list, err := golistPackages(ld.Context, ld.Dir, ld.Env, export, ld.Tests, deps, patterns)
+	rawCfg := newRawConfig(&ld.Config)
+	list, err := golistPackages(rawCfg, patterns...)
 	if _, ok := err.(GoTooOldError); ok {
 		return loaderFallback(ld.Dir, ld.Env, patterns)
 	}

go/packages/raw.go

@@ -0,0 +1,48 @@
+// Copyright 2018 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 packages
+
+import (
+	"context"
+	"fmt"
+	"os"
+)
+
+// This file contains the structs needed at the seam between the packages
+// loader and the underlying build tool
+
+// rawConfig specifies details about what raw package information is needed
+// and how the underlying build tool should load package data.
+type rawConfig struct {
+	Context context.Context
+	Dir     string
+	Env     []string
+	Export  bool
+	Tests   bool
+	Deps    bool
+}
+
+func newRawConfig(cfg *Config) *rawConfig {
+	rawCfg := &rawConfig{
+		Context: cfg.Context,
+		Dir:     cfg.Dir,
+		Env:     cfg.Env,
+		Export:  cfg.Mode > LoadImports && cfg.Mode < LoadAllSyntax,
+		Tests:   cfg.Tests,
+		Deps:    cfg.Mode >= LoadImports,
+	}
+	if rawCfg.Env == nil {
+		rawCfg.Env = os.Environ()
+	}
+	return rawCfg
+}
+
+func (cfg *rawConfig) Flags() []string {
+	return []string{
+		fmt.Sprintf("-test=%t", cfg.Tests),
+		fmt.Sprintf("-export=%t", cfg.Export),
+		fmt.Sprintf("-deps=%t", cfg.Deps),
+	}
+}