go/analysis/passes/gofmt: add gofmt analyzer

go/analysis/passes/gofmt/doc.go

@@ -0,0 +1,15 @@
+// Copyright 2026 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 gofmt defines an Analyzer that reports lines that would be
+// changed by gofmt.
+//
+// # Analyzer gofmt
+//
+// gofmt: report lines whose formatting differs from gofmt's
+//
+// This analyzer reports diagnostic warnings for lines in Go source files
+// that are not formatted according to gofmt. Each diagnostic includes a
+// suggested fix to apply the correct formatting.
+package gofmt

go/analysis/passes/gofmt/gofmt.go

@@ -0,0 +1,76 @@
+// Copyright 2026 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 gofmt
+
+import (
+	"bytes"
+	_ "embed"
+	"go/ast"
+	"go/format"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/internal/analysis/analyzerutil"
+	"golang.org/x/tools/internal/diff"
+	"golang.org/x/tools/internal/goplsexport"
+)
+
+//go:embed doc.go
+var doc string
+
+var analyzer = &analysis.Analyzer{
+	Name:             "gofmt",
+	Doc:              analyzerutil.MustExtractDoc(doc, "gofmt"),
+	URL:              "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/gofmt",
+	Run:              run,
+	RunDespiteErrors: true,
+}
+
+func init() {
+	// Export to gopls until this is a published analyzer.
+	goplsexport.GofmtAnalyzer = analyzer
+}
+
+func run(pass *analysis.Pass) (any, error) {
+	for _, file := range pass.Files {
+		if ast.IsGenerated(file) {
+			continue
+		}
+		tokenFile := pass.Fset.File(file.FileStart)
+		filename := tokenFile.Name()
+
+		src, err := pass.ReadFile(filename)
+		if err != nil {
+			continue
+		}
+
+		formatted, err := format.Source(src)
+		if err != nil {
+			continue
+		}
+
+		if bytes.Equal(src, formatted) {
+			continue
+		}
+
+		for _, edit := range diff.Lines(string(src), string(formatted)) {
+			pos := tokenFile.Pos(edit.Start)
+			end := tokenFile.Pos(edit.End)
+			pass.Report(analysis.Diagnostic{
+				Pos:     pos,
+				End:     end,
+				Message: "file not formatted correctly",
+				SuggestedFixes: []analysis.SuggestedFix{{
+					Message: "Format with gofmt",
+					TextEdits: []analysis.TextEdit{{
+						Pos:     pos,
+						End:     end,
+						NewText: []byte(edit.New),
+					}},
+				}},
+			})
+		}
+	}
+	return nil, nil
+}

go/analysis/passes/gofmt/gofmt_test.go

@@ -0,0 +1,19 @@
+// Copyright 2026 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 gofmt_test
+
+import (
+	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+	"golang.org/x/tools/internal/goplsexport"
+
+	_ "golang.org/x/tools/go/analysis/passes/gofmt"
+)
+
+func Test(t *testing.T) {
+	testdata := analysistest.TestData()
+	analysistest.RunWithSuggestedFixes(t, testdata, goplsexport.GofmtAnalyzer, "a")
+}

go/analysis/passes/gofmt/testdata/src/a/a.go

@@ -0,0 +1,9 @@
+package a
+
+import  "fmt" // want "file not formatted correctly"
+
+func f( ) { // want "file not formatted correctly"
+
+	x:=1 // want "file not formatted correctly"
+	fmt.Println(x)
+}

go/analysis/passes/gofmt/testdata/src/a/a.go.golden

@@ -0,0 +1,9 @@
+package a
+
+import "fmt" // want "file not formatted correctly"
+
+func f() { // want "file not formatted correctly"
+
+	x := 1 // want "file not formatted correctly"
+	fmt.Println(x)
+}

gopls/doc/analyzers.md

@@ -3227,6 +3227,16 @@ Default: on.
 
 Package documentation: [framepointer](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/framepointer)
 
+<a id='gofmt'></a>
+## `gofmt`: report lines whose formatting differs from gofmt's
+
+This analyzer reports diagnostic warnings for lines in Go source files that are not formatted according to gofmt. Each diagnostic includes a suggested fix to apply the correct formatting.
+
+
+Default: off. Enable by setting `"analyses": {"gofmt": true}`.
+
+Package documentation: [gofmt](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/gofmt)
+
 <a id='hostport'></a>
 ## `hostport`: check format of addresses passed to net.Dial
 

gopls/internal/doc/api.json

@@ -1496,6 +1496,12 @@
 							"Default": "true",
 							"Status": ""
 						},
+						{
+							"Name": "\"gofmt\"",
+							"Doc": "report lines whose formatting differs from gofmt's\n\nThis analyzer reports diagnostic warnings for lines in Go source files\nthat are not formatted according to gofmt. Each diagnostic includes a\nsuggested fix to apply the correct formatting.",
+							"Default": "false",
+							"Status": ""
+						},
 						{
 							"Name": "\"hostport\"",
 							"Doc": "check format of addresses passed to net.Dial\n\nThis analyzer flags code that produce network address strings using\nfmt.Sprintf, as in this example:\n\n    addr := fmt.Sprintf(\"%s:%d\", host, 12345) // \"will not work with IPv6\"\n    ...\n    conn, err := net.Dial(\"tcp\", addr)       // \"when passed to dial here\"\n\nThe analyzer suggests a fix to use the correct approach, a call to\nnet.JoinHostPort:\n\n    addr := net.JoinHostPort(host, \"12345\")\n    ...\n    conn, err := net.Dial(\"tcp\", addr)\n\nA similar diagnostic and fix are produced for a format string of \"%s:%s\".\n",
@@ -3443,6 +3449,12 @@
 			"URL": "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/framepointer",
 			"Default": true
 		},
+		{
+			"Name": "gofmt",
+			"Doc": "report lines whose formatting differs from gofmt's\n\nThis analyzer reports diagnostic warnings for lines in Go source files\nthat are not formatted according to gofmt. Each diagnostic includes a\nsuggested fix to apply the correct formatting.",
+			"URL": "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/gofmt",
+			"Default": false
+		},
 		{
 			"Name": "hostport",
 			"Doc": "check format of addresses passed to net.Dial\n\nThis analyzer flags code that produce network address strings using\nfmt.Sprintf, as in this example:\n\n    addr := fmt.Sprintf(\"%s:%d\", host, 12345) // \"will not work with IPv6\"\n    ...\n    conn, err := net.Dial(\"tcp\", addr)       // \"when passed to dial here\"\n\nThe analyzer suggests a fix to use the correct approach, a call to\nnet.JoinHostPort:\n\n    addr := net.JoinHostPort(host, \"12345\")\n    ...\n    conn, err := net.Dial(\"tcp\", addr)\n\nA similar diagnostic and fix are produced for a format string of \"%s:%s\".\n",

gopls/internal/settings/analysis.go

@@ -25,6 +25,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/errorsas"
 	"golang.org/x/tools/go/analysis/passes/fieldalignment"
 	"golang.org/x/tools/go/analysis/passes/framepointer"
+	_ "golang.org/x/tools/go/analysis/passes/gofmt"
 	"golang.org/x/tools/go/analysis/passes/hostport"
 	"golang.org/x/tools/go/analysis/passes/httpresponse"
 	"golang.org/x/tools/go/analysis/passes/ifaceassert"
@@ -220,6 +221,9 @@ var DefaultAnalyzers = []*Analyzer{
 	{analyzer: recursiveiter.Analyzer}, // under evaluation
 	{analyzer: writestring.Analyzer},
 
+	// disabled by default
+	{analyzer: goplsexport.GofmtAnalyzer, severity: protocol.SeverityInformation, nonDefault: true},
+
 	// disabled due to high false positives
 	{analyzer: shadow.Analyzer, severity: protocol.SeverityHint, nonDefault: true},         // very noisy
 	{analyzer: fieldalignment.Analyzer, severity: protocol.SeverityHint, nonDefault: true}, // #67762, #76237

internal/goplsexport/export.go

@@ -17,4 +17,5 @@ var (
 	UnsafeFuncsModernizer    *analysis.Analyzer // = modernize.unsafeFuncsAnalyzer
 	AtomicTypesModernizer    *analysis.Analyzer // = modernize.atomicTypesAnalyzer
 	EmbedLitModernizer       *analysis.Analyzer // = modernize.embedLitAnalyzer
+	GofmtAnalyzer            *analysis.Analyzer // = gofmt.analyzer
 )