Remove 'defaults' channel from environment.yaml and add libint2 symlink workaround to CI

Author: JMorado

.github/workflows/ci.yml

@@ -51,6 +51,15 @@ jobs:
           environment-file: environment.yaml
           auto-activate-base: false
 
+      - name: Fix libint2 soname (horton compiled against libint2.so.2 / libint2.2.dylib)
+        run: |
+          if [ -f "$CONDA_PREFIX/lib/libint2.so" ] && [ ! -f "$CONDA_PREFIX/lib/libint2.so.2" ]; then
+            ln -sf "$CONDA_PREFIX/lib/libint2.so" "$CONDA_PREFIX/lib/libint2.so.2"
+          fi
+          if [ -f "$CONDA_PREFIX/lib/libint2.dylib" ] && [ ! -f "$CONDA_PREFIX/lib/libint2.2.dylib" ]; then
+            ln -sf "$CONDA_PREFIX/lib/libint2.dylib" "$CONDA_PREFIX/lib/libint2.2.dylib"
+          fi
+
       - name: Install package + test dependencies
         run: pip install -e ".[test]"
 

README.md

@@ -93,6 +93,26 @@ xdm_results = session.calculator.calculate_xdm_moments(
 )
 ```
 
+## Troubleshooting
+
+### `ImportError` when importing HORTON (`libint2` not found)
+
+On some systems, HORTON is compiled against a versioned `libint2` (e.g. `libint2.so.2` on Linux, `libint2.2.dylib` on macOS), but conda-forge only installs the unversioned library. If you see an error like:
+
+```
+ImportError: libint2.so.2: cannot open shared object file: No such file or directory
+```
+
+Create the missing symlink manually:
+
+```bash
+# Linux
+ln -sf "$CONDA_PREFIX/lib/libint2.so" "$CONDA_PREFIX/lib/libint2.so.2"
+
+# macOS
+ln -sf "$CONDA_PREFIX/lib/libint2.dylib" "$CONDA_PREFIX/lib/libint2.2.dylib"
+```
+
 ## Acknowledgments
 
 Some implementations in this package, such as the Newton-Raphson algorithm for the Becke-Roussel (BR) exchange model, are based on [postg](https://github.com/aoterodelaroza/postg). As a state-of-the-art package for XDM calculations, postg serves as an essential reference for accuracy and methodology. The aim of this package is mainly to provide easy-to-use access to a broader range of partitioning schemes beyond Hirshfeld.

environment.yaml

@@ -1,7 +1,6 @@
 name: pyxdm
 channels:
   - conda-forge
-  - defaults
 dependencies:
   - python>=3.10
   - pip

pyxdm/core/session.py

@@ -13,8 +13,8 @@
 
 try:
     import horton as ht
-except ImportError:
-    logger.error("horton package is required for XDM calculations")
+except ImportError as e:
+    logger.error("horton package is required for XDM calculations.")
     sys.exit(1)