improve and test PmgVaspPspDirError msg in PotcarSingle.from_symbol_and_functional

Author: janosh

src/pymatgen/io/vasp/inputs.py

@@ -2277,9 +2277,7 @@ def from_symbol_and_functional(
         functional_subdir = SETTINGS.get("PMG_VASP_PSP_SUB_DIRS", {}).get(functional, cls.functional_dir[functional])
         PMG_VASP_PSP_DIR = SETTINGS.get("PMG_VASP_PSP_DIR")
         if PMG_VASP_PSP_DIR is None:
-            raise PmgVaspPspDirError(
-                f"No POTCAR for {symbol} with {functional=} found. Please set the PMG_VASP_PSP_DIR in .pmgrc.yaml."
-            )
+            raise PmgVaspPspDirError("Set PMG_VASP_PSP_DIR=<directory-path> in .pmgrc.yaml (needed to find POTCARs)")
         if not os.path.isdir(PMG_VASP_PSP_DIR):
             raise FileNotFoundError(f"{PMG_VASP_PSP_DIR=} does not exist.")
 

tests/io/vasp/test_inputs.py

@@ -28,6 +28,7 @@
     Incar,
     Kpoints,
     KpointsSupportedModes,
+    PmgVaspPspDirError,
     Poscar,
     Potcar,
     PotcarSingle,
@@ -1211,7 +1212,16 @@ def test_from_symbol_and_functional_raises(self):
         # test FileNotFoundError on non-existent PMG_VASP_PSP_DIR in SETTINGS
         PMG_VASP_PSP_DIR = "missing-dir"
         symbol, functional = "Fe", "PBE_64"
-        with (
+        with (  # test PMG_VASP_PSP_DIR not set in SETTINGS
+            patch.dict(SETTINGS, PMG_VASP_PSP_DIR=None),
+            pytest.raises(
+                PmgVaspPspDirError,
+                match=re.escape("Set PMG_VASP_PSP_DIR=<directory-path> in .pmgrc.yaml (needed to find POTCARs)"),
+            ),
+        ):
+            PotcarSingle.from_symbol_and_functional(symbol, functional)
+
+        with (  # test FileNotFoundError on non-existent PMG_VASP_PSP_DIR in SETTINGS
             patch.dict(SETTINGS, PMG_VASP_PSP_DIR=PMG_VASP_PSP_DIR),
             pytest.raises(FileNotFoundError, match=f"{PMG_VASP_PSP_DIR=} does not exist."),
         ):