make "garble version" include VCS information

When someone builds garble from a git clone,
the resulting binary used to not contain any information:

	$ garble version
	(devel)

Since Go 1.18, VCS information is stamped by default into binaries.
We now print it, alongside any other available build settings:

	$ garble version
	mvdan.cc/garble (devel)

	Build settings:
	       -compiler gc
	     CGO_ENABLED 1
	          GOARCH amd64
	            GOOS linux
	         GOAMD64 v3
	             vcs git
	    vcs.revision 91ea246
	        vcs.time 2022-03-18T13:45:11Z
	    vcs.modified true

Note that it's still possible for a garble build to contain no useful
version information, such as when built via "go build -buildvcs=false".
However, if a user opts into omitting the information, it's on them to
figure out what version of garble they actually built.

While here, bump test-gotip.

Fixes #491.

.github/workflows/test.yml

@@ -72,7 +72,7 @@ jobs:
     steps:
     - name: Install Go
       env:
-        GO_COMMIT: e475cf2e705d4eda8647426e060898ab3f643610 # 2022-03-14
+        GO_COMMIT: 80a7504a13a5dccb60757d1fc66d71bcba359799 # 2022-03-25
       run: |
         cd $HOME
         mkdir $HOME/gotip

main.go

@@ -42,11 +42,7 @@ import (
 	"mvdan.cc/garble/internal/literals"
 )
 
-var (
-	flagSet = flag.NewFlagSet("garble", flag.ContinueOnError)
-
-	version = "(devel)" // to match the default from runtime/debug
-)
+var flagSet = flag.NewFlagSet("garble", flag.ContinueOnError)
 
 var (
 	flagLiterals bool
@@ -328,15 +324,47 @@ func mainErr(args []string) error {
 			fmt.Fprintf(os.Stderr, "usage: garble version\n")
 			return errJustExit(2)
 		}
-		// don't overwrite the version if it was set by -ldflags=-X
-		if info, ok := debug.ReadBuildInfo(); ok && version == "(devel)" {
-			mod := &info.Main
-			if mod.Replace != nil {
-				mod = mod.Replace
+		info, ok := debug.ReadBuildInfo()
+		if !ok {
+			// The build binary was stripped of build info?
+			// Could be the case if garble built itself.
+			fmt.Println("unknown")
+			return nil
+		}
+		mod := &info.Main
+		if mod.Replace != nil {
+			mod = mod.Replace
+		}
+
+		// For the tests.
+		if v := os.Getenv("GARBLE_TEST_VERSION"); v != "" {
+			mod.Version = v
+		}
+		if v := os.Getenv("GARBLE_TEST_SUM"); v != "" {
+			mod.Sum = v
+		}
+		if v := os.Getenv("GARBLE_TEST_SETTINGS"); v != "" {
+			var extra []debug.BuildSetting
+			if err := json.Unmarshal([]byte(v), &extra); err != nil {
+				return err
+			}
+			info.Settings = append(info.Settings, extra...)
+		}
+
+		fmt.Printf("%s %s %s\n\n", mod.Path, mod.Version, mod.Sum)
+		fmt.Printf("Build settings:\n")
+		for _, setting := range info.Settings {
+			if setting.Value == "" {
+				continue // do empty build settings even matter?
 			}
-			version = mod.Version
+			// The padding helps keep readability by aligning:
+			//
+			//   veryverylong.key value
+			//          short.key some-other-value
+			//
+			// Empirically, 16 is enough; the longest key seen is "vcs.revision".
+			fmt.Printf("%16s %s\n", setting.Key, setting.Value)
 		}
-		fmt.Println(version)
 		return nil
 	case "reverse":
 		return commandReverse(args)

testdata/scripts/help.txt

@@ -77,8 +77,32 @@ stderr 'must precede command, like: garble -seed=random build \./pkg'
 [windows] ! garble C:\does\not\exist\compile
 stderr 'not running "garble \[command\]"'
 
+# Test the version command. Note that test binaries exclude VCS build info,
+# and we reuse the test binary for garble itself, so that's missing.
+# To avoid building another garble binary,
+# and to be able to use static VCS info, use an environment variable.
+# First, test without the information, and then with it.
+#
+# Note that Go 1.18.0 shipped with -buildvcs=true for "go test",
+# so it's a special case that we need to handle until 1.18.1 is out.
 garble version
-stdout 'devel|^v0'
+stdout -count=1 'mvdan.cc/garble \(devel\)'
+stdout -count=1 'Build settings'
+stdout -count=3 '-compiler|GOOS|GOARCH'
+[go1.19] ! stdout 'vcs'
+
+env GARBLE_TEST_VERSION='v0.88.99'
+env GARBLE_TEST_SUM='h1:someBase64epYSXwA'
+# Obtained from a real build while developing.
+env GARBLE_TEST_SETTINGS='[{"Key":"vcs","Value":"git"},{"Key":"vcs.revision","Value":"91ea246349544769f5100c29f79cb0f173abfeea"},{"Key":"vcs.time","Value":"2022-03-18T13:45:11Z"},{"Key":"vcs.modified","Value":"true"}]'
+garble version
+stdout -count=1 'mvdan.cc/garble v0\.88\.99 h1:someBase64epYSXwA'
+stdout -count=1 'Build settings'
+stdout -count=3 '-compiler|GOOS|GOARCH'
+[go1.19] stdout -count=1 'vcs git'
+[go1.19] stdout -count=1 'vcs.revision 91ea246349544769f5100c29f79cb0f173abfeea'
+[go1.19] stdout -count=1 'vcs.time 2022-03-18T13:45:11Z'
+[go1.19] stdout -count=1 'vcs.modified true'
 
 ! garble version -flag
 stderr 'usage: garble version'