Guard against adding deprecated legacy variables

.github/workflows/legacy.yml

@@ -0,0 +1,32 @@
+# This workflow validates that (new) variables are not referenced as deprecated legacy variables
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
+
+name: Guard against legacy variables
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ '**' ]
+
+jobs:
+  legacy-validation:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Python 3.11
+      uses: actions/setup-python@v4
+      with:
+        python-version: 3.11
+
+    - name: Install requirements
+      run: pip install -r requirements.txt
+
+    - name: Install pytest
+      run: pip install pytest
+
+    - name: Run the legacy validation
+      run: pytest tests/test_legacy.py

requirements.txt

@@ -1 +1 @@
-nomenclature-iamc >= 0.12
+nomenclature-iamc >= 0.16

tests/test_legacy.py

@@ -0,0 +1,25 @@
+from nomenclature import DataStructureDefinition
+
+
+def test_legacy_variables():
+    # Check that (new) variables are not referenced as deprecated legacy variables
+    dsd = DataStructureDefinition("definitions/", dimensions=["variable"])
+    existing_variables = list(dsd.variable)
+
+    legacy_variables = {}
+    for code, attrs in dsd.variable.items():
+        for project in ["navigate", "engage"]:
+            if project in attrs.extra_attributes:
+                legacy_var = attrs.__getattr__(project)
+                if legacy_var in existing_variables:
+                    legacy_variables[legacy_var] = code
+
+    if legacy_variables:
+        error = [
+            f"'{legacy_var}' -> '{code}'" + "\n"
+            for legacy_var, code in legacy_variables.items()
+        ]
+
+        raise ValueError(
+            "Deprecated variables from legacy projects:\n" f"{''.join(error)}"
+        )