cmd/go: add go generate -skip flag

Following proposal discussion in #38687, add go generate -skip
to allow easier skipping of specific //go:generate directives.

Fixes #38687.

Change-Id: Ied5b4042965dd6a2b93c1c517045fccae2d95c3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/421440
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

3 files changed, 41 insertions, 7 deletions

diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index a3c1fecb91..ce152171fd 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -594,7 +594,7 @@
 //
 // The generator is run in the package's source directory.
 //
-// Go generate accepts one specific flag:
+// Go generate accepts two specific flags:
 //
 //	-run=""
 //		if non-empty, specifies a regular expression to select
@@ -602,6 +602,13 @@
 //		any trailing spaces and final newline) matches the
 //		expression.
 //
+//	-skip=""
+//		if non-empty, specifies a regular expression to suppress
+//		directives whose full original source text (excluding
+//		any trailing spaces and final newline) matches the
+//		expression. If a directive matches both the -run and
+//		the -skip arguments, it is skipped.
+//
 // It also accepts the standard build flags including -v, -n, and -x.
 // The -v flag prints the names of packages and files as they are
 // processed.
diff --git a/src/cmd/go/internal/generate/generate.go b/src/cmd/go/internal/generate/generate.go
index 65e7148aa8..3eda6c7145 100644
--- a/src/cmd/go/internal/generate/generate.go
+++ b/src/cmd/go/internal/generate/generate.go
@@ -133,7 +133,7 @@ all further processing for that package.
 
 The generator is run in the package's source directory.
 
-Go generate accepts one specific flag:
+Go generate accepts two specific flags:
 
 	-run=""
 		if non-empty, specifies a regular expression to select
@@ -141,6 +141,13 @@ Go generate accepts one specific flag:
 		any trailing spaces and final newline) matches the
 		expression.
 
+	-skip=""
+		if non-empty, specifies a regular expression to suppress
+		directives whose full original source text (excluding
+		any trailing spaces and final newline) matches the
+		expression. If a directive matches both the -run and
+		the -skip arguments, it is skipped.
+
 It also accepts the standard build flags including -v, -n, and -x.
 The -v flag prints the names of packages and files as they are
 processed.
@@ -156,11 +163,15 @@ For more about specifying packages, see 'go help packages'.
 var (
 	generateRunFlag string         // generate -run flag
 	generateRunRE   *regexp.Regexp // compiled expression for -run
+
+	generateSkipFlag string         // generate -skip flag
+	generateSkipRE   *regexp.Regexp // compiled expression for -skip
 )
 
 func init() {
 	work.AddBuildFlags(CmdGenerate, work.DefaultBuildFlags)
 	CmdGenerate.Flag.StringVar(&generateRunFlag, "run", "", "")
+	CmdGenerate.Flag.StringVar(&generateSkipFlag, "skip", "", "")
 }
 
 func runGenerate(ctx context.Context, cmd *base.Command, args []string) {
@@ -171,6 +182,13 @@ func runGenerate(ctx context.Context, cmd *base.Command, args []string) {
 			log.Fatalf("generate: %s", err)
 		}
 	}
+	if generateSkipFlag != "" {
+		var err error
+		generateSkipRE, err = regexp.Compile(generateSkipFlag)
+		if err != nil {
+			log.Fatalf("generate: %s", err)
+		}
+	}
 
 	cfg.BuildContext.BuildTags = append(cfg.BuildContext.BuildTags, "generate")
 
@@ -291,10 +309,11 @@ func (g *Generator) run() (ok bool) {
 		if !isGoGenerate(buf) {
 			continue
 		}
-		if generateRunFlag != "" {
-			if !generateRunRE.Match(bytes.TrimSpace(buf)) {
-				continue
-			}
+		if generateRunFlag != "" && !generateRunRE.Match(bytes.TrimSpace(buf)) {
+			continue
+		}
+		if generateSkipFlag != "" && generateSkipRE.Match(bytes.TrimSpace(buf)) {
+			continue
 		}
 
 		g.setEnv()
diff --git a/src/cmd/go/testdata/script/generate.txt b/src/cmd/go/testdata/script/generate.txt
index 73f5bbd57a..58777c5865 100644
--- a/src/cmd/go/testdata/script/generate.txt
+++ b/src/cmd/go/testdata/script/generate.txt
@@ -17,11 +17,19 @@ stdout 'Now is the time for all good men'
 go generate './generate/substitution.go'
 stdout $GOARCH' substitution.go:7 pabc xyzp/substitution.go/123'
 
-# Test go generate's run flag
+# Test go generate's run and skip flags
 go generate -run y.s './generate/flag.go'
 stdout 'yes' # flag.go should select yes
 ! stdout 'no' # flag.go should not select no
 
+go generate -skip th..sand './generate/flag.go'
+stdout 'yes' # flag.go should select yes
+! stdout 'no' # flag.go should not select no
+
+go generate -run . -skip th..sand './generate/flag.go'
+stdout 'yes' # flag.go should select yes
+! stdout 'no' # flag.go should not select no
+
 # Test go generate provides the right "$GOPACKAGE" name in an x_test
 go generate './generate/env_test.go'
 stdout 'main_test'