internal/lsp/cache: move mod-related functions and file

This is a pure move with no code changes.
Rename parse_mod.go to mod_tidy.go since it's changed a bit.
Move the modfile.go functions into view.go since (1) Heschi doesn't
like spreading methods into multiple files and (2) it only has 2
functions in it anyway.

Change-Id: If0d7e4b50ac22c57302d90d68c2181dbb3ca8b87
Reviewed-on: https://go-review.googlesource.com/c/tools/+/216142
Reviewed-by: Rohan Challa <[email protected]>
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: stamblerre

internal/lsp/cache/parse_mod.go renamed to internal/lsp/cache/mod_tidy.go

@@ -11,6 +11,8 @@ import (
 	"fmt"
 	"go/ast"
 	"go/token"
+	"io"
+	"io/ioutil"
 	stdlog "log"
 	"os"
 	"path/filepath"
@@ -23,6 +25,7 @@ import (
 	"golang.org/x/tools/internal/imports"
 	"golang.org/x/tools/internal/lsp/debug"
 	"golang.org/x/tools/internal/lsp/source"
+	"golang.org/x/tools/internal/lsp/telemetry"
 	"golang.org/x/tools/internal/memoize"
 	"golang.org/x/tools/internal/span"
 	"golang.org/x/tools/internal/telemetry/log"
@@ -660,3 +663,85 @@ func (v *view) setGoEnv(ctx context.Context, dir string, env []string) (string,
 	}
 	return "", nil
 }
+
+// This function will return the main go.mod file for this folder if it exists and whether the -modfile
+// flag exists for this version of go.
+func (v *view) modfileFlagExists(ctx context.Context, env []string) (bool, error) {
+	// Check the go version by running "go list" with modules off.
+	// Borrowed from internal/imports/mod.go:620.
+	const format = `{{range context.ReleaseTags}}{{if eq . "go1.14"}}{{.}}{{end}}{{end}}`
+	folder := v.folder.Filename()
+	stdout, err := source.InvokeGo(ctx, folder, append(env, "GO111MODULE=off"), "list", "-e", "-f", format)
+	if err != nil {
+		return false, err
+	}
+	// If the output is not go1.14 or an empty string, then it could be an error.
+	lines := strings.Split(stdout.String(), "\n")
+	if len(lines) < 2 && stdout.String() != "" {
+		log.Error(ctx, "unexpected stdout when checking for go1.14", errors.Errorf("%q", stdout), telemetry.Directory.Of(folder))
+		return false, nil
+	}
+	return lines[0] == "go1.14", nil
+}
+
+func (v *view) setModuleInformation(ctx context.Context, gomod string, modfileFlagEnabled bool) error {
+	modFile := strings.TrimSpace(gomod)
+	if modFile == os.DevNull {
+		return nil
+	}
+	v.mod = moduleInformation{
+		realMod: span.FileURI(modFile),
+	}
+	// The user has disabled the use of the -modfile flag.
+	if !modfileFlagEnabled {
+		return nil
+	}
+	if modfileFlag, err := v.modfileFlagExists(ctx, v.Options().Env); err != nil {
+		return err
+	} else if !modfileFlag {
+		return nil
+	}
+	// Copy the current go.mod file into the temporary go.mod file.
+	// The file's name will be of the format go.1234.mod.
+	// It's temporary go.sum file should have the corresponding format of go.1234.sum.
+	tempModFile, err := ioutil.TempFile("", "go.*.mod")
+	if err != nil {
+		return err
+	}
+	defer tempModFile.Close()
+
+	origFile, err := os.Open(modFile)
+	if err != nil {
+		return err
+	}
+	defer origFile.Close()
+
+	if _, err := io.Copy(tempModFile, origFile); err != nil {
+		return err
+	}
+	v.mod.tempMod = span.FileURI(tempModFile.Name())
+
+	// Copy go.sum file as well (if there is one).
+	sumFile := filepath.Join(filepath.Dir(modFile), "go.sum")
+	stat, err := os.Stat(sumFile)
+	if err != nil || !stat.Mode().IsRegular() {
+		return nil
+	}
+	contents, err := ioutil.ReadFile(sumFile)
+	if err != nil {
+		return err
+	}
+	if err := ioutil.WriteFile(tempSumFile(tempModFile.Name()), contents, stat.Mode()); err != nil {
+		return err
+	}
+	return nil
+}
+
+// tempSumFile returns the path to the copied temporary go.sum file.
+// It simply replaces the extension of the temporary go.mod file with "sum".
+func tempSumFile(filename string) string {
+	if filename == "" {
+		return ""
+	}
+	return filename[:len(filename)-len("mod")] + "sum"
+}