[dev.typeparams] cmd/gofmt: add the -G flag to allow generic code

Add support for type parameters to cmd/gofmt, gated behind the -G flag.

The test was based on a test from go/printer, slightly modified to
exercise more formatting.

Change-Id: I489bcb3ad06e1ed4e6d9f5bc79825e60dcfe9953
Reviewed-on: https://go-review.googlesource.com/c/go/+/291011
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

diff --git a/src/cmd/gofmt/doc.go b/src/cmd/gofmt/doc.go
index e34066559415e76e6cbea9664d1a19939ca176fe..68476e7d4433d04da2c87ebfd0641aaba3a96597 100644 (file)
--- a/src/cmd/gofmt/doc.go
+++ b/src/cmd/gofmt/doc.go
@@ -26,6 +26,9 @@ The flags are:
                Do not print reformatted sources to standard output.
                If a file's formatting is different from gofmt's, print its name
                to standard output.
+       -G
+               Allow generic code, using type parameters.
+               See golang.org/issues/43651 for more information.
        -r rule
                Apply the rewrite rule to the source before reformatting.
        -s

diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index 2793c2c2a43f0891f9d91c0cdb94515c72572e50..b82aa7e7a9357daa014ed8eb59d195b86af959c8 100644 (file)
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -26,12 +26,13 @@ import (
 
 var (
        // main operation modes
-       list        = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
-       write       = flag.Bool("w", false, "write result to (source) file instead of stdout")
-       rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
-       simplifyAST = flag.Bool("s", false, "simplify code")
-       doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
-       allErrors   = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")
+       list            = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
+       write           = flag.Bool("w", false, "write result to (source) file instead of stdout")
+       rewriteRule     = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
+       simplifyAST     = flag.Bool("s", false, "simplify code")
+       doDiff          = flag.Bool("d", false, "display diffs instead of rewriting files")
+       allErrors       = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")
+       allowTypeParams = flag.Bool("G", false, "allow generic code")
 
        // debugging
        cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
@@ -71,6 +72,9 @@ func initParserMode() {
        if *allErrors {
                parserMode |= parser.AllErrors
        }
+       if *allowTypeParams {
+               parserMode |= parser.ParseTypeParams
+       }
 }
 
 func isGoFile(f fs.DirEntry) bool {

diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index bf2adfe64c52b1ef9362cd803cb04473b8ce0dae..60e4f2e03d2e0e093ba96a24f79b9f34782e85c5 100644 (file)
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -77,6 +77,8 @@ func runTest(t *testing.T, in, out string) {
                case "-stdin":
                        // fake flag - pretend input is from stdin
                        stdin = true
+               case "-G":
+                       *allowTypeParams = true
                default:
                        t.Errorf("unrecognized flag name: %s", name)
                }

diff --git a/src/cmd/gofmt/testdata/typeparams.golden b/src/cmd/gofmt/testdata/typeparams.golden
new file mode 100644 (file)
index 0000000..35f08d1
--- /dev/null
+++ b/src/cmd/gofmt/testdata/typeparams.golden
@@ -0,0 +1,35 @@
+// 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.
+
+//gofmt -G
+
+package typeparams
+
+type T[P any] struct{}
+type T[P1, P2, P3 any] struct{}
+
+type T[P C] struct{}
+type T[P1, P2, P3 C] struct{}
+
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1, P2, P3]] struct{}
+
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
+
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface {
+       m1(P1)
+       type P2, P3
+}](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](T1[P], T2[P]) T3[P]
+
+func (x T[P]) m()
+func (T[P]) m(x T[P]) P
+
+func _() {
+       type _ []T[P]
+       var _ []T[P]
+       _ = []T[P]{}
+}

diff --git a/src/cmd/gofmt/testdata/typeparams.input b/src/cmd/gofmt/testdata/typeparams.input
new file mode 100644 (file)
index 0000000..7f3212c
--- /dev/null
+++ b/src/cmd/gofmt/testdata/typeparams.input
@@ -0,0 +1,32 @@
+// 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.
+
+//gofmt -G
+
+package typeparams
+
+type T[  P any] struct{}
+type T[P1, P2, P3 any] struct{}
+
+type T[P C] struct{}
+type T[P1,P2, P3 C] struct{}
+
+type T[P C[P]] struct{}
+type T[P1, P2, P3 C[P1,P2,P3]] struct{}
+
+func f[P any](x P)
+func f[P1, P2, P3 any](x1 P1, x2 P2, x3 P3) struct{}
+
+func f[P interface{}](x P)
+func f[P1, P2, P3 interface{ m1(P1); type P2, P3 }](x1 P1, x2 P2, x3 P3) struct{}
+func f[P any](T1[P], T2[P]) T3[P]
+
+func (x T[P]) m()
+func ((T[P])) m(x T[P]) P
+
+func _() {
+       type _ []T[P]
+       var _ []T[P]
+       _ = []T[P]{}
+}