internal/lsp: support textDocument/hover for .mod extension

This change implements support for textDocument/hover when it comes to go.mod files.

Updates golang/go#36501

Change-Id: Ie7da0194bb972955b7ab9cf7b9c9972bd9f4b8a9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/220359
Run-TryBot: Rohan Challa <rohan@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/cache/mod.go

@@ -78,6 +78,10 @@ type modData struct {
 	// upgrades is a map of path->version that contains any upgrades for the go.mod.
 	upgrades map[string]string
 
+	// why is a map of path->explanation that contains all the "go mod why" contents
+	// for each require statement.
+	why map[string]string
+
 	// parseErrors are the errors that arise when we diff between a user's go.mod
 	// and the "tidied" go.mod.
 	parseErrors []source.Error
@@ -112,6 +116,15 @@ func (mh *modHandle) Upgrades(ctx context.Context) (*modfile.File, *protocol.Col
 	return data.origParsedFile, data.origMapper, data.upgrades, data.err
 }
 
+func (mh *modHandle) Why(ctx context.Context) (*modfile.File, *protocol.ColumnMapper, map[string]string, error) {
+	v := mh.handle.Get(ctx)
+	if v == nil {
+		return nil, nil, nil, errors.Errorf("no parsed file for %s", mh.File().Identity().URI)
+	}
+	data := v.(*modData)
+	return data.origParsedFile, data.origMapper, data.why, data.err
+}
+
 func (s *snapshot) ModHandle(ctx context.Context, fh source.FileHandle) source.ModHandle {
 	uri := fh.Identity().URI
 	if handle := s.getModHandle(uri); handle != nil {
@@ -165,7 +178,15 @@ func (s *snapshot) ModHandle(ctx context.Context, fh source.FileHandle) source.M
 			}
 		}
 		// Only get dependency upgrades if the go.mod file is the same as the view's.
-		data.upgrades, data.err = dependencyUpgrades(ctx, cfg, folder, data)
+		if err := dependencyUpgrades(ctx, cfg, folder, data); err != nil {
+			data.err = err
+			return data
+		}
+		// Only run "go mod why" if the go.mod file is the same as the view's.
+		if err := goModWhy(ctx, cfg, folder, data); err != nil {
+			data.err = err
+			return data
+		}
 		return data
 	})
 	s.mu.Lock()
@@ -178,9 +199,39 @@ func (s *snapshot) ModHandle(ctx context.Context, fh source.FileHandle) source.M
 	return s.modHandles[uri]
 }
 
-func dependencyUpgrades(ctx context.Context, cfg *packages.Config, folder string, data *modData) (map[string]string, error) {
+func goModWhy(ctx context.Context, cfg *packages.Config, folder string, data *modData) error {
 	if len(data.origParsedFile.Require) == 0 {
-		return nil, nil
+		return nil
+	}
+	// Run "go mod why" on all the dependencies to get information about the usages.
+	inv := gocommand.Invocation{
+		Verb:       "mod",
+		Args:       []string{"why", "-m"},
+		BuildFlags: cfg.BuildFlags,
+		Env:        cfg.Env,
+		WorkingDir: folder,
+	}
+	for _, req := range data.origParsedFile.Require {
+		inv.Args = append(inv.Args, req.Mod.Path)
+	}
+	stdout, err := inv.Run(ctx)
+	if err != nil {
+		return err
+	}
+	whyList := strings.Split(stdout.String(), "\n\n")
+	if len(whyList) <= 1 || len(whyList) > len(data.origParsedFile.Require) {
+		return nil
+	}
+	data.why = make(map[string]string)
+	for i, req := range data.origParsedFile.Require {
+		data.why[req.Mod.Path] = whyList[i]
+	}
+	return nil
+}
+
+func dependencyUpgrades(ctx context.Context, cfg *packages.Config, folder string, data *modData) error {
+	if len(data.origParsedFile.Require) == 0 {
+		return nil
 	}
 	// Run "go list -u -m all" to be able to see which deps can be upgraded.
 	inv := gocommand.Invocation{
@@ -192,13 +243,13 @@ func dependencyUpgrades(ctx context.Context, cfg *packages.Config, folder string
 	}
 	stdout, err := inv.Run(ctx)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	upgradesList := strings.Split(stdout.String(), "\n")
 	if len(upgradesList) <= 1 {
-		return nil, nil
+		return nil
 	}
-	upgrades := make(map[string]string)
+	data.upgrades = make(map[string]string)
 	for _, upgrade := range upgradesList[1:] {
 		// Example: "github.com/x/tools v1.1.0 [v1.2.0]"
 		info := strings.Split(upgrade, " ")
@@ -208,9 +259,9 @@ func dependencyUpgrades(ctx context.Context, cfg *packages.Config, folder string
 		dep, version := info[0], info[2]
 		latest := version[1:]                    // remove the "["
 		latest = strings.TrimSuffix(latest, "]") // remove the "]"
-		upgrades[dep] = latest
+		data.upgrades[dep] = latest
 	}
-	return upgrades, nil
+	return nil
 }
 
 func (mh *modHandle) Tidy(ctx context.Context) (*modfile.File, *protocol.ColumnMapper, map[string]*modfile.Require, []source.Error, error) {

internal/lsp/hover.go

@@ -7,36 +7,21 @@ package lsp
 import (
 	"context"
 
+	"golang.org/x/tools/internal/lsp/mod"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 )
 
 func (s *Server) hover(ctx context.Context, params *protocol.HoverParams) (*protocol.Hover, error) {
-	snapshot, fh, ok, err := s.beginFileRequest(params.TextDocument.URI, source.Go)
+	snapshot, fh, ok, err := s.beginFileRequest(params.TextDocument.URI, source.UnknownKind)
 	if !ok {
 		return nil, err
 	}
-	ident, err := source.Identifier(ctx, snapshot, fh, params.Position)
-	if err != nil {
-		return nil, nil
+	switch fh.Identity().Kind {
+	case source.Mod:
+		return mod.Hover(ctx, snapshot, fh, params.Position)
+	case source.Go:
+		return source.Hover(ctx, snapshot, fh, params.Position)
 	}
-	h, err := ident.Hover(ctx)
-	if err != nil {
-		return nil, err
-	}
-	rng, err := ident.Range()
-	if err != nil {
-		return nil, err
-	}
-	hover, err := source.FormatHover(h, snapshot.View().Options())
-	if err != nil {
-		return nil, err
-	}
-	return &protocol.Hover{
-		Contents: protocol.MarkupContent{
-			Kind:  snapshot.View().Options().PreferredContentFormat,
-			Value: hover,
-		},
-		Range: rng,
-	}, nil
+	return nil, nil
 }

internal/lsp/mod/hover.go

@@ -0,0 +1,149 @@
+package mod
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"go/token"
+	"strings"
+
+	"golang.org/x/mod/modfile"
+	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/lsp/source"
+	"golang.org/x/tools/internal/span"
+	"golang.org/x/tools/internal/telemetry/trace"
+)
+
+func Hover(ctx context.Context, snapshot source.Snapshot, fh source.FileHandle, position protocol.Position) (*protocol.Hover, error) {
+	realURI, _ := snapshot.View().ModFiles()
+	// Only get hover information on the go.mod for the view.
+	if realURI == "" || fh.Identity().URI != realURI {
+		return nil, nil
+	}
+	ctx, done := trace.StartSpan(ctx, "mod.Hover")
+	defer done()
+
+	file, m, why, err := snapshot.ModHandle(ctx, fh).Why(ctx)
+	if err != nil {
+		return nil, err
+	}
+	// Get the position of the cursor.
+	spn, err := m.PointSpan(position)
+	if err != nil {
+		return nil, err
+	}
+	hoverRng, err := spn.Range(m.Converter)
+	if err != nil {
+		return nil, err
+	}
+
+	var req *modfile.Require
+	var startPos, endPos int
+	for _, r := range file.Require {
+		dep := []byte(r.Mod.Path)
+		s, e := r.Syntax.Start.Byte, r.Syntax.End.Byte
+		i := bytes.Index(m.Content[s:e], dep)
+		if i == -1 {
+			continue
+		}
+		// Shift the start position to the location of the
+		// dependency within the require statement.
+		startPos, endPos = s+i, s+i+len(dep)
+		if token.Pos(startPos) <= hoverRng.Start && hoverRng.Start <= token.Pos(endPos) {
+			req = r
+			break
+		}
+	}
+	if req == nil || why == nil {
+		return nil, nil
+	}
+	explanation, ok := why[req.Mod.Path]
+	if !ok {
+		return nil, nil
+	}
+	// Get the range to highlight for the hover.
+	line, col, err := m.Converter.ToPosition(startPos)
+	if err != nil {
+		return nil, err
+	}
+	start := span.NewPoint(line, col, startPos)
+
+	line, col, err = m.Converter.ToPosition(endPos)
+	if err != nil {
+		return nil, err
+	}
+	end := span.NewPoint(line, col, endPos)
+
+	spn = span.New(fh.Identity().URI, start, end)
+	rng, err := m.Range(spn)
+	if err != nil {
+		return nil, err
+	}
+	options := snapshot.View().Options()
+	explanation = formatExplanation(explanation, req, options)
+	return &protocol.Hover{
+		Contents: protocol.MarkupContent{
+			Kind:  options.PreferredContentFormat,
+			Value: explanation,
+		},
+		Range: rng,
+	}, nil
+}
+
+func formatExplanation(text string, req *modfile.Require, options source.Options) string {
+	text = strings.TrimSuffix(text, "\n")
+	splt := strings.Split(text, "\n")
+	length := len(splt)
+
+	var b strings.Builder
+	// Write the heading as an H3.
+	b.WriteString("##" + splt[0])
+	if options.PreferredContentFormat == protocol.Markdown {
+		b.WriteString("\n\n")
+	} else {
+		b.WriteRune('\n')
+	}
+
+	// If the explanation is 2 lines, then it is of the form:
+	// # golang.org/x/text/encoding
+	// (main module does not need package golang.org/x/text/encoding)
+	if length == 2 {
+		b.WriteString(splt[1])
+		return b.String()
+	}
+
+	imp := splt[length-1]
+	target := imp
+	if strings.ToLower(options.LinkTarget) == "pkg.go.dev" {
+		target = strings.Replace(target, req.Mod.Path, req.Mod.String(), 1)
+	}
+	target = fmt.Sprintf("https://%s/%s", options.LinkTarget, target)
+
+	b.WriteString("This module is necessary because ")
+	msg := fmt.Sprintf("[%s](%s) is imported in", imp, target)
+	b.WriteString(msg)
+
+	// If the explanation is 3 lines, then it is of the form:
+	// # golang.org/x/tools
+	// modtest
+	// golang.org/x/tools/go/packages
+	if length == 3 {
+		msg := fmt.Sprintf(" `%s`.", splt[1])
+		b.WriteString(msg)
+		return b.String()
+	}
+
+	// If the explanation is more than 3 lines, then it is of the form:
+	// # golang.org/x/text/language
+	// rsc.io/quote
+	// rsc.io/sampler
+	// golang.org/x/text/language
+	b.WriteString(":\n```text")
+	dash := ""
+	for _, imp := range splt[1 : length-1] {
+		dash += "-"
+		b.WriteString("\n" + dash + " " + imp)
+	}
+	b.WriteString("\n```")
+	return b.String()
+}

internal/lsp/source/hover.go

@@ -44,6 +44,32 @@ type HoverInformation struct {
 	comment *ast.CommentGroup
 }
 
+func Hover(ctx context.Context, snapshot Snapshot, fh FileHandle, position protocol.Position) (*protocol.Hover, error) {
+	ident, err := Identifier(ctx, snapshot, fh, position)
+	if err != nil {
+		return nil, nil
+	}
+	h, err := ident.Hover(ctx)
+	if err != nil {
+		return nil, err
+	}
+	rng, err := ident.Range()
+	if err != nil {
+		return nil, err
+	}
+	hover, err := FormatHover(h, snapshot.View().Options())
+	if err != nil {
+		return nil, err
+	}
+	return &protocol.Hover{
+		Contents: protocol.MarkupContent{
+			Kind:  snapshot.View().Options().PreferredContentFormat,
+			Value: hover,
+		},
+		Range: rng,
+	}, nil
+}
+
 func (i *IdentifierInfo) Hover(ctx context.Context) (*HoverInformation, error) {
 	ctx, done := trace.StartSpan(ctx, "source.Hover")
 	defer done()

internal/lsp/source/view.go

@@ -271,6 +271,11 @@ type ModHandle interface {
 	// for the go.mod file. Note that this will only work if the go.mod is the view's go.mod.
 	// If the file is not available, returns nil and an error.
 	Upgrades(ctx context.Context) (*modfile.File, *protocol.ColumnMapper, map[string]string, error)
+
+	// Why returns the parsed modfile, a mapper, and any explanations why a dependency should be
+	// in the go.mod file. Note that this will only work if the go.mod is the view's go.mod.
+	// If the file is not available, returns nil and an error.
+	Why(ctx context.Context) (*modfile.File, *protocol.ColumnMapper, map[string]string, error)
 }
 
 // ModTidyHandle represents a handle to the modfile for the view.