gopls/internal/lsp/mod: optimizations for mod tidy diagnostics

Run mod tidy diagnostics in parallel, and don't parse files to determine
missing imports if there are no missing requires.

BenchmarkDiagnoseSave: 8s->1.8s

For golang/go#60089

Change-Id: I5d41827914e4eb9264b16ed14af323c017eb327c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/496439
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

Author: findleyr

gopls/doc/commands.md

@@ -267,6 +267,9 @@ Args:
 	"URI": string,
 	// The module path to remove.
 	"ModulePath": string,
+	// If the module is tidied apart from the one unused diagnostic, we can
+	// run `go get module@none`, and then run `go mod tidy`. Otherwise, we
+	// must make textual edits.
 	"OnlyDiagnostic": bool,
 }
 ```

gopls/internal/lsp/cache/mod_tidy.go

@@ -183,7 +183,33 @@ func modTidyDiagnostics(ctx context.Context, snapshot *snapshot, pm *source.Pars
 	// go.mod file. The fixes will be for the go.mod file, but the
 	// diagnostics should also appear in both the go.mod file and the import
 	// statements in the Go files in which the dependencies are used.
+	// Finally, add errors for any unused dependencies.
+	if len(missing) > 0 {
+		missingModuleDiagnostics, err := missingModuleDiagnostics(ctx, snapshot, pm, ideal, missing)
+		if err != nil {
+			return nil, err
+		}
+		diagnostics = append(diagnostics, missingModuleDiagnostics...)
+	}
+
+	// Opt: if this is the only diagnostic, we can avoid textual edits and just
+	// run the Go command.
+	//
+	// See also the documentation for command.RemoveDependencyArgs.OnlyDiagnostic.
+	onlyDiagnostic := len(diagnostics) == 0 && len(unused) == 1
+	for _, req := range unused {
+		srcErr, err := unusedDiagnostic(pm.Mapper, req, onlyDiagnostic)
+		if err != nil {
+			return nil, err
+		}
+		diagnostics = append(diagnostics, srcErr)
+	}
+	return diagnostics, nil
+}
+
+func missingModuleDiagnostics(ctx context.Context, snapshot *snapshot, pm *source.ParsedModule, ideal *modfile.File, missing map[string]*modfile.Require) ([]*source.Diagnostic, error) {
 	missingModuleFixes := map[*modfile.Require][]source.SuggestedFix{}
+	var diagnostics []*source.Diagnostic
 	for _, req := range missing {
 		srcDiag, err := missingModuleDiagnostic(pm, req)
 		if err != nil {
@@ -290,15 +316,6 @@ func modTidyDiagnostics(ctx context.Context, snapshot *snapshot, pm *source.Pars
 			}
 		}
 	}
-	// Finally, add errors for any unused dependencies.
-	onlyDiagnostic := len(diagnostics) == 0 && len(unused) == 1
-	for _, req := range unused {
-		srcErr, err := unusedDiagnostic(pm.Mapper, req, onlyDiagnostic)
-		if err != nil {
-			return nil, err
-		}
-		diagnostics = append(diagnostics, srcErr)
-	}
 	return diagnostics, nil
 }
 

gopls/internal/lsp/command.go

@@ -360,10 +360,9 @@ func (c *commandHandler) RemoveDependency(ctx context.Context, args command.Remo
 		progress: "Removing dependency",
 		forURI:   args.URI,
 	}, func(ctx context.Context, deps commandDeps) error {
-		// If the module is tidied apart from the one unused diagnostic, we can
-		// run `go get module@none`, and then run `go mod tidy`. Otherwise, we
-		// must make textual edits.
-		// TODO(rstambler): In Go 1.17+, we will be able to use the go command
+		// See the documentation for OnlyDiagnostic.
+		//
+		// TODO(rfindley): In Go 1.17+, we will be able to use the go command
 		// without checking if the module is tidy.
 		if args.OnlyDiagnostic {
 			return c.s.runGoModUpdateCommands(ctx, deps.snapshot, args.URI.SpanURI(), func(invoke func(...string) (*bytes.Buffer, error)) error {

gopls/internal/lsp/command/interface.go

@@ -236,7 +236,10 @@ type RemoveDependencyArgs struct {
 	// The go.mod file URI.
 	URI protocol.DocumentURI
 	// The module path to remove.
-	ModulePath     string
+	ModulePath string
+	// If the module is tidied apart from the one unused diagnostic, we can
+	// run `go get module@none`, and then run `go mod tidy`. Otherwise, we
+	// must make textual edits.
 	OnlyDiagnostic bool
 }
 

gopls/internal/lsp/mod/diagnostics.go

@@ -9,11 +9,14 @@ package mod
 import (
 	"context"
 	"fmt"
+	"runtime"
 	"sort"
 	"strings"
+	"sync"
 
 	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/semver"
+	"golang.org/x/sync/errgroup"
 	"golang.org/x/tools/gopls/internal/govulncheck"
 	"golang.org/x/tools/gopls/internal/lsp/command"
 	"golang.org/x/tools/gopls/internal/lsp/protocol"
@@ -58,24 +61,36 @@ func VulnerabilityDiagnostics(ctx context.Context, snapshot source.Snapshot) (ma
 }
 
 func collectDiagnostics(ctx context.Context, snapshot source.Snapshot, diagFn func(context.Context, source.Snapshot, source.FileHandle) ([]*source.Diagnostic, error)) (map[span.URI][]*source.Diagnostic, error) {
+
+	g, ctx := errgroup.WithContext(ctx)
+	cpulimit := runtime.GOMAXPROCS(0)
+	g.SetLimit(cpulimit)
+
+	var mu sync.Mutex
 	reports := make(map[span.URI][]*source.Diagnostic)
+
 	for _, uri := range snapshot.ModFiles() {
-		fh, err := snapshot.ReadFile(ctx, uri)
-		if err != nil {
-			return nil, err
-		}
-		reports[fh.URI()] = []*source.Diagnostic{}
-		diagnostics, err := diagFn(ctx, snapshot, fh)
-		if err != nil {
-			return nil, err
-		}
-		for _, d := range diagnostics {
-			fh, err := snapshot.ReadFile(ctx, d.URI)
+		uri := uri
+		g.Go(func() error {
+			fh, err := snapshot.ReadFile(ctx, uri)
 			if err != nil {
-				return nil, err
+				return err
 			}
-			reports[fh.URI()] = append(reports[fh.URI()], d)
-		}
+			diagnostics, err := diagFn(ctx, snapshot, fh)
+			if err != nil {
+				return err
+			}
+			for _, d := range diagnostics {
+				mu.Lock()
+				reports[d.URI] = append(reports[fh.URI()], d)
+				mu.Unlock()
+			}
+			return nil
+		})
+	}
+
+	if err := g.Wait(); err != nil {
+		return nil, err
 	}
 	return reports, nil
 }