Use plugin API for Solver instantiation

.github/workflows/main.yml

@@ -29,6 +29,8 @@ jobs:
       matrix:
         os: [macos-latest, ubuntu-latest, windows-latest]
         pyver: ["3.7", "3.8", "3.9", "3.10"]
+    env:
+      PYTHONUNBUFFERED: True
     steps:
       - name: Print github context
         run: |
@@ -59,7 +61,6 @@ jobs:
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
           PYTHONIOENCODING: utf-8
-          PYTHONUNBUFFERED: True
           # Uncomment to run within conda build
           # RUN_EXAMPLES: "1"
         run: |
@@ -116,7 +117,14 @@ jobs:
           source $CONDA/etc/profile.d/conda.sh
           conda activate constructor
           mkdir -p examples_artifacts/
-          python -u scripts/run_examples.py --keep-artifacts=examples_artifacts/
+          python scripts/run_examples.py --keep-artifacts=examples_artifacts/
+      - name: Test with conda-libmamba-solver
+        run: |
+          source $CONDA/etc/profile.d/conda.sh
+          conda activate constructor
+          conda install -yq conda-libmamba-solver
+          conda list
+          CONDA_SOLVER=libmamba CONDA_VERBOSITY=1 constructor examples/noconda/ --output-dir=examples_artifacts/
       - name: Upload the example installers as artifacts
         if: github.event_name == 'pull_request' && matrix.pyver == '3.9'
         uses: actions/upload-artifact@v3

CONSTRUCT.md

@@ -73,6 +73,10 @@ included in a `conda create --file` command. Packages may also be specified
 by an exact URL; e.g.,
 `https://repo.anaconda.com/pkgs/main/osx-64/openssl-1.0.2o-h26aff7b_0.tar.bz2`.
 
+The specs will be solved with the solver configured for your `base` conda installation,
+if any. Starting with conda 22.11, this behavior can be overriden with the
+`CONDA_SOLVER` environment variable.
+
 ## `user_requested_specs`
 
 _required:_ no<br/>
@@ -137,13 +141,15 @@ that, and the temporary environment will be removed. This ensures that
 constructor is using the precise local conda configuration to discover
 and install the packages. The created environment MUST include `python`.
 
+Read notes about the solver in the `specs` field.
+
 ## `transmute_file_type`
 
 _required:_ no<br/>
 _type:_ string<br/>
 File type extension for the files to be transmuted into. Currently supports
 only '.conda'. See conda-package-handling for supported extension names.
-If left empty, no transumating is done.
+If left empty, no transmuting is done.
 
 ## `conda_default_channels`
 

constructor/conda_interface.py

@@ -51,9 +51,9 @@
     except ImportError:
         from conda.models.package_cache_record import PackageCacheRecord as _PackageCacheRecord
     try:
-        from conda.core.solve import _get_solver_class
-        _Solver = _get_solver_class()
-    except ImportError:
+        from conda.base.context import context
+        _Solver = context.plugin_manager.get_cached_solver_backend()
+    except (ImportError, AttributeError):
         from conda.core.solve import Solver as _Solver
 
     # used by fcp.py

constructor/construct.py

@@ -58,6 +58,10 @@
 included in a `conda create --file` command. Packages may also be specified
 by an exact URL; e.g.,
 `https://repo.anaconda.com/pkgs/main/osx-64/openssl-1.0.2o-h26aff7b_0.tar.bz2`.
+
+The specs will be solved with the solver configured for your `base` conda installation,
+if any. Starting with conda 22.11, this behavior can be overriden with the
+`CONDA_SOLVER` environment variable.
 '''),
 
     ('user_requested_specs',                  False, (list, str), '''
@@ -108,12 +112,14 @@
 that, and the temporary environment will be removed. This ensures that
 constructor is using the precise local conda configuration to discover
 and install the packages. The created environment MUST include `python`.
+
+Read notes about the solver in the `specs` field.
 '''),
 
     ('transmute_file_type', False, str, '''
 File type extension for the files to be transmuted into. Currently supports
 only '.conda'. See conda-package-handling for supported extension names.
-If left empty, no transumating is done.
+If left empty, no transmuting is done.
 '''),
 
     ('conda_default_channels', False, list, '''

news/531-enable-alternative-solvers

@@ -1,6 +1,6 @@
 ### Enhancements:
 
-* Enable alternative solvers by obeying `CONDA_EXPERIMENTAL_SOLVER` if set and available. (#531)
+* Enable alternative solvers by obeying `CONDA_SOLVER` if set and available. (#531, #597)
 
 ### Bug fixes: