Add interpreter constraints rule

src/python/pants/backend/python/register.py

@@ -8,6 +8,7 @@
 from pants.backend.python.rules import (
   download_pex_bin,
   inject_init,
+  interpreter_constraints,
   pex,
   python_run_binary,
   python_test_runner,
@@ -99,6 +100,7 @@ def rules():
   return (
     download_pex_bin.rules() +
     inject_init.rules() +
+    interpreter_constraints.rules() +
     python_test_runner.rules() +
     python_run_binary.rules() +
     python_native_code_rules() +

src/python/pants/backend/python/rules/interpreter_constraints.py

@@ -0,0 +1,42 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from dataclasses import dataclass
+from typing import FrozenSet, List, Tuple
+
+from pants.backend.python.subsystems.python_setup import PythonSetup
+from pants.engine.legacy.structs import PythonTargetAdaptor
+from pants.engine.rules import RootRule, rule
+
+
+@dataclass(frozen=True)
+class BuildConstraintsForAdaptors:
+  adaptors: Tuple[PythonTargetAdaptor]
+
+
+@dataclass(frozen=True)
+class PexInterpreterContraints:
+  constraint_set: FrozenSet[str] = frozenset()
+
+  def generate_pex_arg_list(self) -> List[str]:
+    args = []
+    for constraint in self.constraint_set:
+      args.extend(["--interpreter-constraint", constraint])
+    return args
+
+
+@rule
+def handle_constraints(build_constraints_for_adaptors: BuildConstraintsForAdaptors, python_setup: PythonSetup) -> PexInterpreterContraints:
+  interpreter_constraints = frozenset(
+    [constraint
+    for target_adaptor in build_constraints_for_adaptors.adaptors
+    for constraint in python_setup.compatibility_or_constraints(
+      getattr(target_adaptor, 'compatibility', None)
+    )]
+  )
+
+  yield PexInterpreterContraints(constraint_set=interpreter_constraints)
+
+
+def rules():
+  return [handle_constraints, RootRule(BuildConstraintsForAdaptors)]

src/python/pants/backend/python/rules/pex.py

@@ -6,6 +6,7 @@
 
 from pants.backend.python.rules.download_pex_bin import DownloadedPexBin
 from pants.backend.python.rules.hermetic_pex import HermeticPex
+from pants.backend.python.rules.interpreter_constraints import PexInterpreterContraints
 from pants.backend.python.subsystems.python_native_code import PexBuildEnvironment
 from pants.backend.python.subsystems.python_setup import PythonSetup
 from pants.backend.python.subsystems.subprocess_environment import SubprocessEncodingEnvironment
@@ -31,7 +32,7 @@ class CreatePex:
   """Represents a generic request to create a PEX from its inputs."""
   output_filename: str
   requirements: Tuple[str] = ()
-  interpreter_constraints: Tuple[str] = ()
+  interpreter_constraints: PexInterpreterContraints = PexInterpreterContraints()
   entry_point: Optional[str] = None
   input_files_digest: Optional[Digest] = None
 
@@ -57,9 +58,7 @@ def create_pex(
   """Returns a PEX with the given requirements, optional entry point, and optional
   interpreter constraints."""
 
-  interpreter_constraint_args = []
-  for constraint in request.interpreter_constraints:
-    interpreter_constraint_args.extend(["--interpreter-constraint", constraint])
+  interpreter_constraint_args = request.interpreter_constraints.generate_pex_arg_list()
 
   argv = ["--output-file", request.output_filename]
   if request.entry_point is not None:
@@ -118,7 +117,7 @@ class RunnablePex:
 # necessarily the interpreter that PEX will use to execute the generated .pex file.
 @rule
 def pex_execute_request(
-  runnable_pex: RunnablePex,
+  runnable_pex: RunnablePex, #TODO if this rule is a Pex the rule graph blows up wtf?
   subprocess_encoding_environment: SubprocessEncodingEnvironment,
   python_setup: PythonSetup
   ) -> ExecuteProcessRequest:

src/python/pants/backend/python/rules/python_run_binary.py

@@ -2,6 +2,10 @@
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
 from pants.backend.python.rules.inject_init import InjectedInitDigest
+from pants.backend.python.rules.interpreter_constraints import (
+  BuildConstraintsForAdaptors,
+  PexInterpreterContraints,
+)
 from pants.backend.python.rules.pex import CreatePex, RunnablePex
 from pants.backend.python.subsystems.python_setup import PythonSetup
 from pants.backend.python.targets.python_binary import PythonBinary
@@ -25,13 +29,9 @@ def run_python_binary(python_binary_target: PythonBinaryAdaptor,
   all_targets = transitive_hydrated_targets.closure
   all_target_adaptors = [t.adaptor for t in all_targets]
 
-  interpreter_constraints = {
-    constraint
-    for target_adaptor in all_target_adaptors
-    for constraint in python_setup.compatibility_or_constraints(
-      getattr(target_adaptor, 'compatibility', None)
-    )
-  }
+
+  interpreter_constraints = yield Get(PexInterpreterContraints,
+      BuildConstraintsForAdaptors(adaptors=tuple(all_target_adaptors)))
 
   source_root_stripped_sources = yield [
     Get(SourceRootStrippedSources, HydratedTarget, target_adaptor)
@@ -74,7 +74,7 @@ def run_python_binary(python_binary_target: PythonBinaryAdaptor,
   create_requirements_pex = CreatePex(
     output_filename=output_thirdparty_requirements_pex_filename,
     requirements=tuple(sorted(all_requirements)),
-    interpreter_constraints=tuple(sorted(interpreter_constraints)),
+    interpreter_constraints=interpreter_constraints,
     entry_point=entry_point,
     input_files_digest=merged_input_files,
   )

src/python/pants/backend/python/rules/python_test_runner.py

@@ -2,6 +2,10 @@
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
 from pants.backend.python.rules.inject_init import InjectedInitDigest
+from pants.backend.python.rules.interpreter_constraints import (
+  BuildConstraintsForAdaptors,
+  PexInterpreterContraints,
+)
 from pants.backend.python.rules.pex import CreatePex, Pex
 from pants.backend.python.subsystems.pytest import PyTest
 from pants.backend.python.subsystems.python_setup import PythonSetup
@@ -33,13 +37,8 @@ def run_python_test(
   )
   all_targets = transitive_hydrated_targets.closure
 
-  interpreter_constraints = {
-    constraint
-    for target_adaptor in all_targets
-    for constraint in python_setup.compatibility_or_constraints(
-      getattr(target_adaptor, 'compatibility', None)
-    )
-  }
+  interpreter_constraints = yield Get(PexInterpreterContraints,
+      BuildConstraintsForAdaptors(adaptors=tuple(all_targets)))
 
   # Produce a pex containing pytest and all transitive 3rdparty requirements.
   output_pytest_requirements_pex_filename = 'pytest-with-requirements.pex'
@@ -58,7 +57,7 @@ def run_python_test(
     Pex, CreatePex(
       output_filename=output_pytest_requirements_pex_filename,
       requirements=tuple(sorted(all_requirements)),
-      interpreter_constraints=tuple(sorted(interpreter_constraints)),
+      interpreter_constraints=interpreter_constraints,
       entry_point="pytest:main",
     )
   )