Add *_constrains run_export types

conda_build/render.py

@@ -410,31 +410,44 @@ def add_upstream_pins(m, permit_unsatisfiable_variants, exclude_pattern):
                                                     permit_unsatisfiable_variants, exclude_pattern)
         if m.noarch or m.noarch_python:
             extra_run_specs = set(extra_run_specs_from_host.get('noarch', []))
+            extra_run_constrained_specs = set([])
         else:
             extra_run_specs = set(extra_run_specs_from_host.get('strong', []) +
                                   extra_run_specs_from_host.get('weak', []) +
                                   extra_run_specs_from_build.get('strong', []))
+            extra_run_constrained_specs = set(
+                extra_run_specs_from_host.get('strong_constrains', []) +
+                extra_run_specs_from_host.get('weak_constrains', []) +
+                extra_run_specs_from_build.get('strong_constrains', [])
+            )
     else:
         host_deps = []
         host_unsat = []
         if m.noarch or m.noarch_python:
             if m.build_is_host:
                 extra_run_specs = set(extra_run_specs_from_build.get('noarch', []))
+                extra_run_constrained_specs = set([])
                 build_deps = set(build_deps or []).update(extra_run_specs_from_build.get('noarch', []))
             else:
                 extra_run_specs = set([])
+                extra_run_constrained_specs = set([])
                 build_deps = set(build_deps or [])
         else:
             extra_run_specs = set(extra_run_specs_from_build.get('strong', []))
+            extra_run_constrained_specs = set(extra_run_specs_from_build.get('strong_constrains', []))
             if m.build_is_host:
                 extra_run_specs.update(extra_run_specs_from_build.get('weak', []))
+                extra_run_constrained_specs.update(extra_run_specs_from_build.get('weak_constrains', []))
                 build_deps = set(build_deps or []).update(extra_run_specs_from_build.get('weak', []))
             else:
                 host_deps = set(extra_run_specs_from_build.get('strong', []))
 
     run_deps = extra_run_specs | set(utils.ensure_list(requirements.get('run')))
+    run_constrained_deps = extra_run_constrained_specs | set(utils.ensure_list(requirements.get('run_constrained')))
 
-    for section, deps in (('build', build_deps), ('host', host_deps), ('run', run_deps)):
+    for section, deps in (
+        ('build', build_deps), ('host', host_deps), ('run', run_deps), ('run_constrained', run_constrained_deps),
+    ):
         if deps:
             requirements[section] = list(deps)
 

conda_build/utils.py

@@ -115,6 +115,8 @@ def glob(pathname, recursive=True):
     "weak",
     "strong",
     "noarch",
+    "weak_constrains",
+    "strong_constrains",
 }
 
 PY_TMPL = """

docs/source/resources/define-metadata.rst

@@ -747,6 +747,30 @@ pinning relative to versions present at build time:
 With this example, if libpng were version 1.6.34, this pinning expression would
 evaluate to ``>=1.6.34,<1.7``.
 
+If build and link dependencies need to impose constraints on the run environment
+but not necessarily pull in additional packages, then this can be done by
+altering the :ref:`Run_constrained` entries. In addtion to ``weak``/``strong``
+``run_exports`` which add to the ``run`` requirements, ``weak_constrains`` and
+``strong_constrains`` add to the ``run_constrained`` requirements.
+With these, e.g., minimum versions of compatible but not required packages (like
+optional plugins for the linked dependency, or certain system attributes) can be
+expressed:
+
+..
+   TODO: Replace example below with actual ones that use constrains run_exports.
+
+.. code-block:: yaml
+
+   requirements:
+     build:
+       - build-tool                 # has a strong run_constrained export
+     host:
+       - link-dependency            # has a weak run_constrained export
+     run:
+     run_constrained:
+       # - system-dependency >=min  <-- implicitly added by build-tool
+       # - optional-plugin >=min    <-- implicitly added by link-dependency
+
 Note that ``run_exports`` can be specified both in the build section and on
 a per-output basis for split packages.
 

news/gh-4125-run_exports-constains.rst

@@ -0,0 +1,25 @@
+Enhancements:
+-------------
+
+* Add weak_constrains and strong_constrains run_exports types.
+
+Bug fixes:
+----------
+
+* <news item>
+
+Deprecations:
+-------------
+
+* <news item>
+
+Docs:
+-----
+
+* <news item>
+
+Other:
+------
+
+* <news item>
+

tests/test-recipes/metadata/_run_exports_constrains/meta.yaml

@@ -0,0 +1,29 @@
+package:
+  name: test_run_exports_constrains
+  version: 1.0
+
+outputs:
+  - name: run_exports_constrains
+    build:
+      run_exports:
+        strong:
+          - strong_run_export
+        weak:
+          - weak_run_export
+        strong_constrains:
+          - strong_constrains_export
+        weak_constrains:
+          - weak_constrains_export
+
+  - name: run_exports_constrains_only_weak
+    build:
+      run_exports:
+        weak:
+          - weak_run_export
+        weak_constrains:
+          - weak_constrains_export
+
+  - name: strong_run_export
+  - name: weak_run_export
+  - name: strong_constrains_export
+  - name: weak_constrains_export

tests/test_api_build.py

@@ -1052,6 +1052,43 @@ def test_run_exports_noarch_python(testing_metadata, testing_config):
     assert 'python 3.6 with_run_exports' not in m.meta['requirements'].get('run', [])
 
 
+def test_run_exports_constrains(testing_metadata, testing_config, testing_workdir):
+    api.build(os.path.join(metadata_dir, '_run_exports_constrains'), config=testing_config,
+              notest=True)
+
+    testing_metadata.meta['requirements']['build'] = ['run_exports_constrains']
+    testing_metadata.meta['requirements']['host'] = []
+    api.output_yaml(testing_metadata, 'in_build/meta.yaml')
+    m = api.render(os.path.join(testing_workdir, 'in_build'), config=testing_config)[0][0]
+    reqs_set = lambda section: set(m.meta['requirements'].get(section, []))
+    assert {'strong_run_export'} == reqs_set('run')
+    assert {'strong_constrains_export'} == reqs_set('run_constrained')
+
+    testing_metadata.meta['requirements']['build'] = []
+    testing_metadata.meta['requirements']['host'] = ['run_exports_constrains']
+    api.output_yaml(testing_metadata, 'in_host/meta.yaml')
+    m = api.render(os.path.join(testing_workdir, 'in_host'), config=testing_config)[0][0]
+    reqs_set = lambda section: set(m.meta['requirements'].get(section, []))
+    assert {'strong_run_export', 'weak_run_export'} == reqs_set('run')
+    assert {'strong_constrains_export', 'weak_constrains_export'} == reqs_set('run_constrained')
+
+    testing_metadata.meta['requirements']['build'] = ['run_exports_constrains_only_weak']
+    testing_metadata.meta['requirements']['host'] = []
+    api.output_yaml(testing_metadata, 'only_weak_in_build/meta.yaml')
+    m = api.render(os.path.join(testing_workdir, 'only_weak_in_build'), config=testing_config)[0][0]
+    reqs_set = lambda section: set(m.meta['requirements'].get(section, []))
+    assert set() == reqs_set('run')
+    assert set() == reqs_set('run_constrained')
+
+    testing_metadata.meta['requirements']['build'] = []
+    testing_metadata.meta['requirements']['host'] = ['run_exports_constrains_only_weak']
+    api.output_yaml(testing_metadata, 'only_weak_in_host/meta.yaml')
+    m = api.render(os.path.join(testing_workdir, 'only_weak_in_host'), config=testing_config)[0][0]
+    reqs_set = lambda section: set(m.meta['requirements'].get(section, []))
+    assert {'weak_run_export'} == reqs_set('run')
+    assert {'weak_constrains_export'} == reqs_set('run_constrained')
+
+
 def test_pin_subpackage_exact(testing_config):
     recipe = os.path.join(metadata_dir, '_pin_subpackage_exact')
     ms = api.render(recipe, config=testing_config)