gopls/internal/hooks: clean language version before passing to gofumpt

Fixes golang/go#61692

Change-Id: I97bd85c063ac1f525fd01c2b1a8b5ffe574e1c66
Reviewed-on: https://go-review.googlesource.com/c/tools/+/514815
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Peter Weinberger <pjw@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>

gopls/internal/hooks/gofumpt_118.go

@@ -9,16 +9,70 @@ package hooks
 
 import (
 	"context"
+	"fmt"
 
 	"golang.org/x/tools/gopls/internal/lsp/source"
 	"mvdan.cc/gofumpt/format"
 )
 
 func updateGofumpt(options *source.Options) {
 	options.GofumptFormat = func(ctx context.Context, langVersion, modulePath string, src []byte) ([]byte, error) {
+		fixedVersion, err := fixLangVersion(langVersion)
+		if err != nil {
+			return nil, err
+		}
 		return format.Source(src, format.Options{
-			LangVersion: langVersion,
+			LangVersion: fixedVersion,
 			ModulePath:  modulePath,
 		})
 	}
 }
+
+// fixLangVersion function cleans the input so that gofumpt doesn't panic. It is
+// rather permissive, and accepts version strings that aren't technically valid
+// in a go.mod file.
+//
+// More specifically, it looks for an optional 'v' followed by 1-3
+// '.'-separated numbers. The resulting string is stripped of any suffix beyond
+// this expected version number pattern.
+//
+// See also golang/go#61692: gofumpt does not accept the new language versions
+// appearing in go.mod files (e.g. go1.21rc3).
+func fixLangVersion(input string) (string, error) {
+	bad := func() (string, error) {
+		return "", fmt.Errorf("invalid language version syntax %q", input)
+	}
+	if input == "" {
+		return input, nil
+	}
+	i := 0
+	if input[0] == 'v' { // be flexible about 'v'
+		i++
+	}
+	// takeDigits consumes ascii numerals 0-9 and reports if at least one was
+	// consumed.
+	takeDigits := func() bool {
+		found := false
+		for ; i < len(input) && '0' <= input[i] && input[i] <= '9'; i++ {
+			found = true
+		}
+		return found
+	}
+	if !takeDigits() { // versions must start with at least one number
+		return bad()
+	}
+
+	// Accept optional minor and patch versions.
+	for n := 0; n < 2; n++ {
+		if i < len(input) && input[i] == '.' {
+			// Look for minor/patch version.
+			i++
+			if !takeDigits() {
+				i--
+				break
+			}
+		}
+	}
+	// Accept any suffix.
+	return input[:i], nil
+}

gopls/internal/hooks/gofumpt_118_test.go

@@ -0,0 +1,53 @@
+// Copyright 2022 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.
+
+//go:build go1.18
+// +build go1.18
+
+package hooks
+
+import "testing"
+
+func TestFixLangVersion(t *testing.T) {
+	tests := []struct {
+		input, want string
+		wantErr     bool
+	}{
+		{"", "", false},
+		{"1.18", "1.18", false},
+		{"v1.18", "v1.18", false},
+		{"1.21", "1.21", false},
+		{"1.21rc3", "1.21", false},
+		{"1.21.0", "1.21.0", false},
+		{"1.21.1", "1.21.1", false},
+		{"v1.21.1", "v1.21.1", false},
+		{"v1.21.0rc1", "v1.21.0", false}, // not technically valid, but we're flexible
+		{"v1.21.0.0", "v1.21.0", false},  // also technically invalid
+		{"1.1", "1.1", false},
+		{"v1", "v1", false},
+		{"1", "1", false},
+		{"v1.21.", "v1.21", false}, // also invalid
+		{"1.21.", "1.21", false},
+
+		// Error cases.
+		{"rc1", "", true},
+		{"x1.2.3", "", true},
+	}
+
+	for _, test := range tests {
+		got, err := fixLangVersion(test.input)
+		if test.wantErr {
+			if err == nil {
+				t.Errorf("fixLangVersion(%q) succeeded unexpectedly", test.input)
+			}
+			continue
+		}
+		if err != nil {
+			t.Fatalf("fixLangVersion(%q) failed: %v", test.input, err)
+		}
+		if got != test.want {
+			t.Errorf("fixLangVersion(%q) = %s, want %s", test.input, got, test.want)
+		}
+	}
+}

gopls/internal/regtest/misc/formatting_test.go

@@ -366,3 +366,30 @@ const Bar = 42
 		}
 	})
 }
+
+func TestGofumpt_Issue61692(t *testing.T) {
+	testenv.NeedsGo1Point(t, 21)
+
+	const input = `
+-- go.mod --
+module foo
+
+go 1.21rc3
+-- foo.go --
+package foo
+
+func _() {
+	foo :=
+		"bar"
+}
+`
+
+	WithOptions(
+		Settings{
+			"gofumpt": true,
+		},
+	).Run(t, input, func(t *testing.T, env *Env) {
+		env.OpenFile("foo.go")
+		env.FormatBuffer("foo.go") // golang/go#61692: must not panic
+	})
+}