fix: use jib-compatible ${param} syntax for template parameters

Changes $${param} to ${param} to match Jib CLI's template parameter
syntax. Escaped parameters use $${param} to produce literal ${param}.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jbadeau

gib/buildfile/parse.go

@@ -174,18 +174,19 @@ func validateOctalPermissions(perm, field string) error {
 	return nil
 }
 
-// substituteParams replaces $${paramName} with values from the params map.
-// Escaped $$$${...} produces a literal $${...}.
+// substituteParams replaces ${paramName} with values from the params map.
+// Compatible with Jib CLI template parameter syntax.
+// Escaped $${...} produces a literal ${...}.
 func substituteParams(content string, params map[string]string) (string, error) {
-	if len(params) == 0 && !strings.Contains(content, "$${") {
+	if len(params) == 0 && !strings.Contains(content, "${") {
 		return content, nil
 	}
 
 	var result strings.Builder
 	i := 0
 	for i < len(content) {
-		// Look for $${
-		idx := strings.Index(content[i:], "$${")
+		// Look for ${
+		idx := strings.Index(content[i:], "${")
 		if idx == -1 {
 			result.WriteString(content[i:])
 			break
@@ -194,15 +195,15 @@ func substituteParams(content string, params map[string]string) (string, error)
 		// Write everything before the match
 		result.WriteString(content[i : i+idx])
 
-		// Check for escaped $$$${
+		// Check for escaped $${
 		if idx > 0 && content[i+idx-1] == '$' {
-			// This is an escaped $$$${...} -> produce literal $${...}
+			// This is an escaped $${...} -> produce literal ${...}
 			// Remove the extra $ we already wrote
 			s := result.String()
 			result.Reset()
 			result.WriteString(s[:len(s)-1]) // remove trailing $
-			result.WriteString("$${")
-			i = i + idx + 3
+			result.WriteString("${")
+			i = i + idx + 2
 			// Find closing }
 			end := strings.Index(content[i:], "}")
 			if end == -1 {
@@ -214,7 +215,7 @@ func substituteParams(content string, params map[string]string) (string, error)
 		}
 
 		// Find closing }
-		paramStart := i + idx + 3
+		paramStart := i + idx + 2
 		end := strings.Index(content[paramStart:], "}")
 		if end == -1 {
 			return "", fmt.Errorf("unclosed template parameter at position %d", i+idx)

gib/buildfile/parse_test.go

@@ -138,23 +138,29 @@ func TestSubstituteParams_NoParams(t *testing.T) {
 }
 
 func TestSubstituteParams_SingleParam(t *testing.T) {
-	result, err := substituteParams("image: $${name}", map[string]string{"name": "alpine"})
+	result, err := substituteParams("image: ${name}", map[string]string{"name": "alpine"})
 	require.NoError(t, err)
 	assert.Equal(t, "image: alpine", result)
 }
 
 func TestSubstituteParams_MultipleParams(t *testing.T) {
-	result, err := substituteParams("$${a}:$${b}", map[string]string{"a": "x", "b": "y"})
+	result, err := substituteParams("${a}:${b}", map[string]string{"a": "x", "b": "y"})
 	require.NoError(t, err)
 	assert.Equal(t, "x:y", result)
 }
 
 func TestSubstituteParams_UnclosedBrace(t *testing.T) {
-	_, err := substituteParams("$${unclosed", nil)
+	_, err := substituteParams("${unclosed", nil)
 	require.Error(t, err)
 	assert.Contains(t, err.Error(), "unclosed")
 }
 
+func TestSubstituteParams_EscapedParam(t *testing.T) {
+	result, err := substituteParams("literal: $${name}", map[string]string{"name": "alpine"})
+	require.NoError(t, err)
+	assert.Equal(t, "literal: ${name}", result)
+}
+
 // --- Validation tests ported from Jib's BuildFileSpecTest ---
 
 func TestParseBytes_EmptyAPIVersion(t *testing.T) {

gib/testdata/buildfiles/template_params.yaml

@@ -1,7 +1,7 @@
 apiVersion: jib/v1alpha1
 kind: BuildFile
 from:
-  image: "$${baseImage}"
+  image: "${baseImage}"
 environment:
-  VERSION: "$${version}"
-user: "$${user}"
+  VERSION: "${version}"
+user: "${user}"