internal/lsp: added a code action which generates key-value pairs of individual

fields and default values between a struct's enclosing braces

Fixes #37576

Author: luciolas

internal/lsp/code_action.go

@@ -134,6 +134,11 @@ func (s *Server) codeAction(ctx context.Context, params *protocol.CodeActionPara
 				})
 			}
 		}
+		fillActions, err := source.FillStruct(ctx, snapshot, fh, params.Range)
+		if err != nil {
+			return nil, err
+		}
+		codeActions = append(codeActions, fillActions...)
 	default:
 		// Unsupported file kind for a code action.
 		return nil, nil

internal/lsp/source/fill_struct.go

@@ -0,0 +1,132 @@
+// Copyright 2020 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 source
+
+import (
+	"context"
+	"fmt"
+	"go/format"
+	"go/types"
+	"strings"
+
+	"golang.org/x/tools/go/ast/astutil"
+	"golang.org/x/tools/internal/lsp/protocol"
+)
+
+// FillStruct completes all of targeted struct's fields with their default values.
+func FillStruct(ctx context.Context, snapshot Snapshot, fh FileHandle, protoRng protocol.Range) ([]protocol.CodeAction, error) {
+
+	pkg, pgh, err := getParsedFile(ctx, snapshot, fh, NarrowestPackageHandle)
+	if err != nil {
+		return nil, fmt.Errorf("getting file for struct fill code action: %v", err)
+	}
+	file, src, m, _, err := pgh.Cached()
+	if err != nil {
+		return nil, err
+	}
+	spn, err := m.PointSpan(protoRng.Start)
+	if err != nil {
+		return nil, err
+	}
+	spanRng, err := spn.Range(m.Converter)
+	if err != nil {
+		return nil, err
+	}
+	path, _ := astutil.PathEnclosingInterval(file, spanRng.Start, spanRng.End)
+	if path == nil {
+		return nil, nil
+	}
+
+	ecl := enclosingCompositeLiteral(path, spanRng.Start, pkg.GetTypesInfo())
+	if ecl == nil || !ecl.isStruct() {
+		return nil, nil
+	}
+
+	// If in F{ Bar<> : V} or anywhere in F{Bar : V, ...}
+	// we should not fill the struct.
+	if ecl.inKey || len(ecl.cl.Elts) != 0 {
+		return nil, nil
+	}
+
+	var codeActions []protocol.CodeAction
+	qfFunc := qualifier(file, pkg.GetTypes(), pkg.GetTypesInfo())
+	switch obj := ecl.clType.(type) {
+	case *types.Struct:
+		fieldCount := obj.NumFields()
+		if fieldCount == 0 {
+			return nil, nil
+		}
+		var edit string
+		for i := 0; i < fieldCount; i++ {
+			field := obj.Field(i)
+			// Ignore fields that are not accessible in the current package.
+			if field.Pkg() != nil && field.Pkg() != pkg.GetTypes() && !field.Exported() {
+				continue
+			}
+
+			label := field.Name()
+			value := formatZeroValue(field.Type(), qfFunc)
+			text := "\n" + label + " : " + value + ","
+			edit += text
+		}
+		edit += "\n"
+
+		// the range of all text between '<>', inclusive. E.g.  {<> ...  <}>
+		mappedRange := newMappedRange(snapshot.View().Session().Cache().FileSet(), m, ecl.cl.Lbrace, ecl.cl.Rbrace+1)
+		protoRange, err := mappedRange.Range()
+		if err != nil {
+			return nil, err
+		}
+		// consider formatting from the first character of the line the lbrace is on.
+		// ToOffset is 1-based
+		beginOffset, err := m.Converter.ToOffset(int(protoRange.Start.Line)+1, 1)
+		if err != nil {
+			return nil, err
+		}
+
+		endOffset, err := m.Converter.ToOffset(int(protoRange.Start.Line)+1, int(protoRange.Start.Character)+1)
+		if err != nil {
+			return nil, err
+		}
+
+		// An increment to make sure the lbrace is included in the slice.
+		endOffset++
+		// Append the edits. Then append the closing brace.
+		sourceCode := string(src[beginOffset:endOffset]) + edit + "}"
+
+		buf, err := format.Source([]byte(sourceCode))
+		if err != nil {
+			return nil, err
+		}
+
+		// it is guranteed that a left brace exists.
+		edit = string(buf[strings.IndexByte(string(buf), '{'):])
+
+		codeActions = append(codeActions, protocol.CodeAction{
+			Title: "Fill struct",
+			Kind:  protocol.RefactorRewrite,
+			Edit: protocol.WorkspaceEdit{
+				DocumentChanges: []protocol.TextDocumentEdit{
+					{
+						TextDocument: protocol.VersionedTextDocumentIdentifier{
+							Version: fh.Identity().Version,
+							TextDocumentIdentifier: protocol.TextDocumentIdentifier{
+								URI: protocol.URIFromSpanURI(fh.Identity().URI),
+							},
+						},
+						Edits: []protocol.TextEdit{
+							{
+								Range:   protoRange,
+								NewText: edit,
+							},
+						},
+					},
+				},
+			},
+		})
+	}
+
+	return codeActions, nil
+}

internal/lsp/source/options.go

@@ -69,6 +69,7 @@ func DefaultOptions() Options {
 					protocol.SourceFixAll:          true,
 					protocol.SourceOrganizeImports: true,
 					protocol.QuickFix:              true,
+					protocol.RefactorRewrite:       true,
 				},
 				Mod: {
 					protocol.SourceOrganizeImports: true,