Better error message for implicit branches

Fixes #407

Signed-off-by: Erik Jaegervall <[email protected]>

Author: erikbosch

src/vss_tools/model.py

@@ -109,7 +109,7 @@ def as_dict(
 class VSSData(VSSRaw):
     model_config = ConfigDict(extra="allow")
     type: NodeType
-    description: str
+    description: str = ""
     comment: str | None = None
     delete: bool = False
     deprecation: str | None = None
@@ -126,6 +126,18 @@ def check_const_uid_format(cls, v: str | None) -> str | None:
         assert bool(re.match(pattern, v)), f"'{v}' is not a valid 'constUID'"
         return v
 
+    @field_validator("description", mode="before")
+    @classmethod
+    def ensure_description(cls, value: Any) -> Any:
+        """Give better explanation for empty description."""
+
+        if value == "":
+            raise ValueError(
+                "all nodes in the final tree must have a description. "
+                "Implicit branches are not allowed in final tree!"
+            )
+        return value
+
 
 class VSSDataBranch(VSSData):
     instances: Any = None

tests/vspec/test_description_error/test_description_error.py

@@ -40,5 +40,5 @@ def test_description_error(vspec_file: str, type_file: str, type_out_file: str,
     assert process.returncode != 0
     log_content = log.read_text()
     print(log_content)
-    assert "'type': 'missing'" in log_content
+    assert "'type': 'value_error'" in log_content
     assert "1 model error(s):" in log_content

tests/vspec/test_overlay/test_overlay.py

@@ -71,5 +71,5 @@ def test_overlay_branch_error(tmp_path):
     assert process.returncode != 0
     log_content = log.read_text()
     assert "'A.AB' has 1 model error(s)" in log_content
-    assert "'type': 'missing'" in log_content
+    assert "'type': 'value_error'" in log_content
     assert "description" in log_content