cmd/go: implement the long-promised -run flag for go generate

Trivial to do, but overlooked for 1.4, which is good because I prefer
the new design, which is just to match against the source code of
the line rather than the command word alone.

Change-Id: Idcf7c4479e97bb7cd732f0d058012321b6057628
Reviewed-on: https://go-review.googlesource.com/9005
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/doc.go

@@ -322,9 +322,10 @@ The generator is run in the package's source directory.
 Go generate accepts one specific flag:
 
 	-run=""
-		TODO: This flag is unimplemented.
-		if non-empty, specifies a regular expression to
-		select directives whose command matches the expression.
+		if non-empty, specifies a regular expression to select
+		directives whose full original source text (excluding
+		any trailing spaces and final newline) matches the
+		expression.
 
 It also accepts the standard build flags -v, -n, and -x.
 The -v flag prints the names of packages and files as they are

src/cmd/go/generate.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"strconv"
 	"strings"
@@ -108,9 +109,10 @@ The generator is run in the package's source directory.
 Go generate accepts one specific flag:
 
 	-run=""
-		TODO: This flag is unimplemented.
-		if non-empty, specifies a regular expression to
-		select directives whose command matches the expression.
+		if non-empty, specifies a regular expression to select
+		directives whose full original source text (excluding
+		any trailing spaces and final newline) matches the
+		expression.
 
 It also accepts the standard build flags -v, -n, and -x.
 The -v flag prints the names of packages and files as they are
@@ -122,7 +124,10 @@ For more about specifying packages, see 'go help packages'.
 	`,
 }
 
-var generateRunFlag string // generate -run flag
+var (
+	generateRunFlag string         // generate -run flag
+	generateRunRE   *regexp.Regexp // compiled expression for -run
+)
 
 func init() {
 	addBuildFlags(cmdGenerate)
@@ -130,6 +135,13 @@ func init() {
 }
 
 func runGenerate(cmd *Command, args []string) {
+	if generateRunFlag != "" {
+		var err error
+		generateRunRE, err = regexp.Compile(generateRunFlag)
+		if err != nil {
+			log.Fatalf("generate: %s", err)
+		}
+	}
 	// Even if the arguments are .go files, this loop suffices.
 	for _, pkg := range packages(args) {
 		for _, file := range pkg.gofiles {
@@ -223,6 +235,11 @@ func (g *Generator) run() (ok bool) {
 		if !isGoGenerate(buf) {
 			continue
 		}
+		if generateRunFlag != "" {
+			if !generateRunRE.Match(bytes.TrimSpace(buf)) {
+				continue
+			}
+		}
 
 		words := g.split(string(buf))
 		if len(words) == 0 {

src/cmd/go/test.bash

@@ -1069,28 +1069,40 @@ fi
 
 TEST 'go generate handles simple command'
 if ! ./testgo generate ./testdata/generate/test1.go > testdata/std.out; then
-	echo "go test ./testdata/generate/test1.go failed to run"
+	echo "go generate ./testdata/generate/test1.go failed to run"
 	ok=false
 elif ! grep 'Success' testdata/std.out > /dev/null; then
-	echo "go test ./testdata/generate/test1.go generated wrong output"
+	echo "go generate ./testdata/generate/test1.go generated wrong output"
 	ok=false
 fi
 
 TEST 'go generate handles command alias'
 if ! ./testgo generate ./testdata/generate/test2.go > testdata/std.out; then
-	echo "go test ./testdata/generate/test2.go failed to run"
+	echo "go generate ./testdata/generate/test2.go failed to run"
 	ok=false
 elif ! grep 'Now is the time for all good men' testdata/std.out > /dev/null; then
-	echo "go test ./testdata/generate/test2.go generated wrong output"
+	echo "go generate ./testdata/generate/test2.go generated wrong output"
 	ok=false
 fi
 
 TEST 'go generate variable substitution'
 if ! ./testgo generate ./testdata/generate/test3.go > testdata/std.out; then
-	echo "go test ./testdata/generate/test3.go failed to run"
+	echo "go generate ./testdata/generate/test3.go failed to run"
 	ok=false
 elif ! grep "$GOARCH test3.go p xyzp/test3.go/123" testdata/std.out > /dev/null; then
-	echo "go test ./testdata/generate/test3.go generated wrong output"
+	echo "go generate ./testdata/generate/test3.go generated wrong output"
+	ok=false
+fi
+
+TEST 'go generate run flag'
+if ! ./testgo generate -run y.s ./testdata/generate/test4.go > testdata/std.out; then
+	echo "go test -run y.s ./testdata/generate/test4.go failed to run"
+	ok=false
+elif ! grep "yes" testdata/std.out > /dev/null; then
+	echo "go generate -run y.s ./testdata/generate/test4.go did not select yes"
+	ok=false
+elif grep "no" testdata/std.out > /dev/null; then
+	echo "go generate -run y.s ./testdata/generate/test4.go selected no"
 	ok=false
 fi
 

src/cmd/go/testdata/generate/test4.go

@@ -0,0 +1,10 @@
+// Copyright 2015 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.
+
+// Test -run flag
+
+//go:generate echo oh yes my man
+//go:generate echo no, no, a thousand times no
+
+package p