Improve shell quoting

Makefile

@@ -9,5 +9,7 @@ acid: acid.go
 	go build -ldflags "-X 'main.projectVersion=$(version)'" -o $@
 acid.1: acid.adoc
 	asciidoctor -b manpage -a release-version=$(version) -o $@ acid.adoc
+test: all
+	go test
 clean:
 	rm -f $(outputs)

acid.adoc

@@ -71,6 +71,9 @@ which has the following fields:
 *CloneURL*::
 	Gitea link for cloning the repository over HTTP.
 
+The special *quote* template function quotes fields for safe usage
+in *sh*(1) command arguments.
+
 Runners
 -------
 Runners receive the following additional environment variables:

acid.go

@@ -93,10 +93,30 @@ func parseConfig(path string) error {
 	}
 
 	var err error
-	gNotifyScript, err = ttemplate.New("notify").Parse(gConfig.Notify)
+	gNotifyScript, err =
+		ttemplate.New("notify").Funcs(shellFuncs).Parse(gConfig.Notify)
 	return err
 }
 
+var shellFuncs = ttemplate.FuncMap{
+	"quote": func(word string) string {
+		// History expansion is annoying, don't let it cut us.
+		if strings.IndexRune(word, '!') >= 0 {
+			return "'" + strings.ReplaceAll(word, "'", `'"'"'`) + "'"
+		}
+
+		const special = "$`\"\\"
+		quoted := []rune{'"'}
+		for _, r := range word {
+			if strings.IndexRune(special, r) >= 0 {
+				quoted = append(quoted, '\\')
+			}
+			quoted = append(quoted, r)
+		}
+		return string(append(quoted, '"'))
+	},
+}
+
 // --- Utilities ---------------------------------------------------------------
 
 func giteaSign(b []byte) string {
@@ -910,8 +930,9 @@ func executorRunTask(ctx context.Context, task Task) error {
 	//  - we might have to clone submodules as well.
 	// Otherwise, we could download a source archive from Gitea,
 	// and use SFTP to upload it to the runner.
-	tmplScript, err := ttemplate.New("script").Parse(rt.Runner.Setup + "\n" +
-		rt.ProjectRunner.Setup + "\n" + rt.ProjectRunner.Build)
+	tmplScript, err := ttemplate.New("script").Funcs(shellFuncs).
+		Parse(rt.Runner.Setup + "\n" +
+			rt.ProjectRunner.Setup + "\n" + rt.ProjectRunner.Build)
 	if err != nil {
 		return fmt.Errorf("script: %w", err)
 	}

acid.yaml.example

@@ -44,9 +44,9 @@ runners:
     setup: |
       set -ex
       sudo pacman -Syu --noconfirm git
-      git clone --recursive '{{.CloneURL}}' '{{.Repo}}'
-      cd '{{.Repo}}'
-      git -c advice.detachedHead=false checkout '{{.Hash}}'
+      git clone --recursive {{quote .CloneURL}} {{quote .Repo}}
+      cd {{quote .Repo}}
+      git -c advice.detachedHead=false checkout {{quote .Hash}}
 
 # Configuration for individual Gitea repositories.
 projects:

acid_test.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"bytes"
+	"testing"
+	ttemplate "text/template"
+)
+
+func TestTemplateQuote(t *testing.T) {
+	// Ideally, we should back-parse it using sh syntax.
+	// This is an unnecessarily fragile test.
+	for _, test := range []struct {
+		input, output string
+	}{
+		{`!!`, `'!!'`},
+		{``, `""`},
+		{`${var}`, `"\${var}"`},
+		{"`cat`", "\"\\`cat\\`\""},
+		{`"魚\"`, `"\"魚\\\""`},
+	} {
+		var b bytes.Buffer
+		err := ttemplate.Must(ttemplate.New("test").
+			Funcs(shellFuncs).Parse("{{quote .}}")).Execute(&b, test.input)
+		if err != nil {
+			t.Errorf("template execution error: %s\n", err)
+		}
+		if b.String() != test.output {
+			t.Errorf("%q should be quoted os %q, not %q\n",
+				test.input, test.output, b.String())
+		}
+	}
+}