update modinfo.txt test for 1.18's build and VCS info

That is, use a very specific build tag and git commit,
and ensure that neither ends up in the binary.

Luckily, we have nothing to do here.
We were already removing _gomod_.go from the build entirely,
and that is still the mechanism that "go build" uses to bundle the data.

Note that the test will still work if git is not installed,
but it will simply not check the VCS side.

Finally, we use "go version -m" to check the existing fields,
which is easier than calling the Go APIs directly.

It seems like "go test" passes on yesterday's Go master, now.
So, enable test-gotip again with that commit hash.

Fixes #385.

.github/workflows/test.yml

@@ -32,13 +32,12 @@ jobs:
         go test -race ./...
 
   test-gotip:
-    if: ${{ false }} # TODO: support Go 1.18, see https://github.com/burrowers/garble/issues/385
     runs-on: ubuntu-latest
-    continue-on-error: true # master breaks sometimes
+    continue-on-error: true # master may not be as stable
     steps:
     - name: Install Go
       env:
-        GO_COMMIT: 46fd547d899286982971474b329d7a95da4f2a6b # 2021-08-11
+        GO_COMMIT: 578ada410de8065dbca46bca08a5993d1307f423 # 2021-11-09
       run: |
         cd $HOME
         mkdir $HOME/gotip

main_test.go

@@ -91,6 +91,7 @@ func TestScripts(t *testing.T) {
 			"binsubstr":         binsubstr,
 			"bincmp":            bincmp,
 			"generate-literals": generateLiterals,
+			"setenvfile":        setenvfile,
 		},
 		UpdateScripts: *update,
 	}
@@ -216,6 +217,17 @@ func generateLiterals(ts *testscript.TestScript, neg bool, args []string) {
 	}
 }
 
+func setenvfile(ts *testscript.TestScript, neg bool, args []string) {
+	if neg {
+		ts.Fatalf("unsupported: ! setenvfile")
+	}
+	if len(args) != 2 {
+		ts.Fatalf("usage: setenvfile name file")
+	}
+
+	ts.Setenv(args[0], ts.ReadFile(args[1]))
+}
+
 func TestSplitFlagsFromArgs(t *testing.T) {
 	t.Parallel()
 	tests := []struct {

testdata/scripts/modinfo.txt

@@ -1,16 +1,31 @@
 env GOPRIVATE=test/main
 
-garble build
-exec ./main
-cmp stderr main.stderr
-! binsubstr main$exe '(devel)'
+[exec:git] exec git init -q
+[exec:git] exec git config user.name "name"
+[exec:git] exec git config user.email "name@email.local"
+[exec:git] exec git add go.mod main.go
+[exec:git] exec git commit -q -m 'very unique commit message'
+[exec:git] exec git rev-parse HEAD
+[exec:git] setenvfile HEAD_COMMIT_SHA stdout
+
+garble build -tags veryuniquebuildtag
+! binsubstr main$exe '(devel)' 'veryuniquebuildtag' ${HEAD_COMMIT_SHA}
+
+go version -m main$exe
+stdout 'main(\.exe)?: unknown'
+stdout -count=1 '^.+$' # expect just one line
 
 [short] stop # no need to verify this with -short
 
-go build
-exec ./main
-cmp stderr main.stderr-orig
-binsubstr main$exe '(devel)'
+go build -tags veryuniquebuildtag
+[!go1.18] binsubstr main$exe '(devel)'
+[go1.18] binsubstr main$exe '(devel)' 'veryuniquebuildtag' ${HEAD_COMMIT_SHA}
+
+go version -m main$exe
+stdout 'path\s*test/main'
+stdout 'mod\s*test/main\s*\(devel\)'
+[go1.18] stdout 'build\s*tags.*veryuniquebuildtag'
+[go1.18] stdout 'build\s*gitrevision.*'${HEAD_COMMIT_SHA}
 
 -- go.mod --
 module test/main
@@ -19,16 +34,4 @@ go 1.17
 -- main.go --
 package main
 
-import "runtime/debug"
-
-func main() {
-	if info, ok := debug.ReadBuildInfo(); ok {
-		println("version", info.Main.Version)
-	} else {
-		println("no version")
-	}
-}
--- main.stderr-orig --
-version (devel)
--- main.stderr --
-no version
+func main() { println("hello world") }