fixes #427: Handle empty strings in elements enabling conditional logic

README.md

@@ -741,6 +741,43 @@ $ docker buildx bake --print webapp
 }
 ```
 
+Example of only adding tags if a variable is not empty using an `notequal` function:
+
+```
+$ cat <<'EOF' > docker-bake.hcl
+variable "TAG" {default="" }
+
+group "default" {
+	targets = [
+		"webapp",
+	]
+}
+
+target "webapp" {
+	context="."
+	dockerfile="Dockerfile"
+	tags = [
+		"my-image:latest",
+		notequal("",TAG) ? "my-image:${TAG}": "",
+	]
+}
+EOF
+
+$ docker buildx bake --print webapp
+{
+   "target": {
+      "webapp": {
+         "context": ".",
+         "dockerfile": "Dockerfile",
+         "tags": [
+            "my-image:latest"
+         ]
+      }
+   }
+}
+```
+
+
 ### `buildx imagetools create [OPTIONS] [SOURCE] [SOURCE...]`
 
 Imagetools contains commands for working with manifest lists in the registry. These commands are useful for inspecting multi-platform build results.

bake/bake.go

@@ -526,6 +526,9 @@ func removeDupes(s []string) []string {
 		if _, ok := seen[v]; ok {
 			continue
 		}
+		if v == "" {
+			continue
+		}
 		seen[v] = struct{}{}
 		s[i] = v
 		i++

bake/hcl.go

@@ -31,6 +31,7 @@ var (
 		"csvdecode":              stdlib.CSVDecodeFunc,
 		"coalesce":               stdlib.CoalesceFunc,
 		"coalescelist":           stdlib.CoalesceListFunc,
+		"compact":                stdlib.CompactFunc,
 		"concat":                 stdlib.ConcatFunc,
 		"contains":               stdlib.ContainsFunc,
 		"distinct":               stdlib.DistinctFunc,