internal/imports: carve out a Source interface for index integration

In preparation for integrating the newly implemented shared module cache
index, carve out a minimal imports.Source interface to be used by
FixImports. For now, this interface has a single implementation,
wrapping the legacy ProcessEnv abstraction, but in the future we can
replace it with an implementation that synthesizes the module cache
index with gopls' own view of the workspace.

This CL intentionally avoids any refactoring aside from extracting the
ProcessEnv-specific logic into a ProcessEnvSource.

For golang/go#36077

Change-Id: I189a908c917aba68868b08845880b1f0aa731180
Reviewed-on: https://go-review.googlesource.com/c/tools/+/623296
Reviewed-by: Peter Weinberger <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Robert Findley <[email protected]>

Author: findleyr

gopls/internal/cache/view.go

@@ -69,6 +69,7 @@ type GoEnv struct {
 	GOFLAGS     string
 	GO111MODULE string
 	GOTOOLCHAIN string
+	GOROOT      string
 
 	// Go version output.
 	GoVersion       int    // The X in Go 1.X
@@ -998,6 +999,7 @@ func FetchGoEnv(ctx context.Context, folder protocol.DocumentURI, opts *settings
 		"GOFLAGS":     &env.GOFLAGS,
 		"GO111MODULE": &env.GO111MODULE,
 		"GOTOOLCHAIN": &env.GOTOOLCHAIN,
+		"GOROOT":      &env.GOROOT,
 	}
 	if err := loadGoEnv(ctx, dir, opts.EnvSlice(), runner, envvars); err != nil {
 		return nil, err

gopls/internal/golang/format.go

@@ -120,7 +120,7 @@ func allImportsFixes(ctx context.Context, snapshot *cache.Snapshot, pgf *parsego
 	defer done()
 
 	if err := snapshot.RunProcessEnvFunc(ctx, func(ctx context.Context, opts *imports.Options) error {
-		allFixEdits, editsPerFix, err = computeImportEdits(ctx, pgf, opts)
+		allFixEdits, editsPerFix, err = computeImportEdits(ctx, pgf, snapshot.View().Folder().Env.GOROOT, opts)
 		return err
 	}); err != nil {
 		return nil, nil, fmt.Errorf("allImportsFixes: %v", err)
@@ -130,11 +130,12 @@ func allImportsFixes(ctx context.Context, snapshot *cache.Snapshot, pgf *parsego
 
 // computeImportEdits computes a set of edits that perform one or all of the
 // necessary import fixes.
-func computeImportEdits(ctx context.Context, pgf *parsego.File, options *imports.Options) (allFixEdits []protocol.TextEdit, editsPerFix []*importFix, err error) {
+func computeImportEdits(ctx context.Context, pgf *parsego.File, goroot string, options *imports.Options) (allFixEdits []protocol.TextEdit, editsPerFix []*importFix, err error) {
 	filename := pgf.URI.Path()
 
 	// Build up basic information about the original file.
-	allFixes, err := imports.FixImports(ctx, filename, pgf.Src, options)
+	isource, err := imports.NewProcessEnvSource(options.Env, filename, pgf.File.Name.Name)
+	allFixes, err := imports.FixImports(ctx, filename, pgf.Src, goroot, options.Env.Logf, isource)
 	if err != nil {
 		return nil, nil, err
 	}