Add :latest tag to renderstatus when no tag provided

Signed-off-by: Aravindhan Ayyanathan <aravindhan.a@est.tech>

Author: aravindtga

e2e/testdata/fn-render/missing-fn-image/.expected/diff.patch

@@ -1,5 +1,5 @@
 diff --git a/Kptfile b/Kptfile
-index 11012de..9fadb6e 100644
+index 11012de..a0f4634 100644
 --- a/Kptfile
 +++ b/Kptfile
 @@ -7,6 +7,26 @@ pipeline:
@@ -22,11 +22,11 @@ index 11012de..9fadb6e 100644
 +    mutationSteps:
 +      - image: ghcr.io/kptdev/krm-functions-catalog/set-namespace:v0.2.0
 +        exitCode: 0
-+      - image: ghcr.io/kptdev/krm-functions-catalog/dne
++      - image: ghcr.io/kptdev/krm-functions-catalog/dne:latest
 +        stderr: |-
 +          docker: Error response from daemon: error from registry: denied
 +          denied
 +
 +          Run 'docker run --help' for more information
 +        exitCode: 125
-+    errorSummary: 'ghcr.io/kptdev/krm-functions-catalog/dne: exit code 125'
++    errorSummary: 'ghcr.io/kptdev/krm-functions-catalog/dne:latest: exit code 125'

e2e/testdata/fn-render/no-op/.expected/diff.patch

@@ -1,5 +1,5 @@
 diff --git a/Kptfile b/Kptfile
-index a7a2d0b..ed39ce3 100644
+index a7a2d0b..3dbfee4 100644
 --- a/Kptfile
 +++ b/Kptfile
 @@ -5,3 +5,12 @@ metadata:
@@ -13,5 +13,5 @@ index a7a2d0b..ed39ce3 100644
 +      reason: RenderSuccess
 +  renderStatus:
 +    mutationSteps:
-+      - image: ghcr.io/kptdev/krm-functions-catalog/no-op
++      - image: ghcr.io/kptdev/krm-functions-catalog/no-op:latest
 +        exitCode: 0

internal/fnruntime/runner.go

@@ -75,6 +75,8 @@ func NewRunner(
 			if err != nil {
 				return nil, err
 			}
+		} else if !hasTagOrDigest(f.Image) {
+			f.Image = f.Image + ":latest"
 		}
 	}
 
@@ -520,3 +522,15 @@ func newFnConfig(fsys filesys.FileSystem, f *kptfilev1.Function, pkgPath types.U
 	// no need to return ConfigMap if no config given
 	return nil, nil
 }
+
+// hasTagOrDigest reports whether the image reference contains an explicit tag or digest.
+func hasTagOrDigest(image string) bool {
+	if strings.Contains(image, "@") {
+		return true
+	}
+	lastSlash := strings.LastIndex(image, "/")
+	if lastSlash == -1 {
+		return strings.Contains(image, ":")
+	}
+	return strings.Contains(image[lastSlash:], ":")
+}

internal/fnruntime/runner_test.go

@@ -658,3 +658,38 @@ func getExpectedPrefix(prefix string) string {
 	}
 	return prefix
 }
+
+func TestHasTagOrDigest(t *testing.T) {
+	tests := []struct {
+		name  string
+		image string
+		want  bool
+	}{
+		// With explicit tag
+		{"tag", "nginx:1.25", true},
+		{"latest tag", "nginx:latest", true},
+		{"full path with tag", "ghcr.io/kptdev/krm-functions-catalog/set-labels:v0.1.5", true},
+
+		// With digest
+		{"digest only", "nginx@sha256:abc123", true},
+		{"full path with digest", "ghcr.io/kptdev/krm-functions-catalog/set-labels@sha256:abc123", true},
+		{"tag and digest", "nginx:1.25@sha256:abc123", true},
+
+		// Without tag or digest
+		{"bare image", "nginx", false},
+		{"full path no tag", "ghcr.io/kptdev/krm-functions-catalog/set-labels", false},
+		{"two-part no tag", "library/nginx", false},
+
+		// Registry with port (should not confuse port colon with tag colon)
+		{"registry port no tag", "localhost:5000/myimage", false},
+		{"registry port with tag", "localhost:5000/myimage:v1", true},
+		{"registry port with digest", "localhost:5000/myimage@sha256:abc123", true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := hasTagOrDigest(tt.image); got != tt.want {
+				t.Errorf("hasTagOrDigest(%q) = %v, want %v", tt.image, got, tt.want)
+			}
+		})
+	}
+}