synthesise a handler module

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

@@ -78,6 +78,9 @@ async def package_python_awslambda(
             layout=layout,
             output_path=field_set.output_path,
             include_requirements=field_set.include_requirements.value,
+            # this isn't built or run via lambdex, but the name is arbitrary, so we stick with the
+            # 'tradition' to reduce churn.
+            reexported_handler_module="lambdex_handler",
         ),
     )
 

src/python/pants/backend/awslambda/python/rules_test.py

@@ -296,27 +296,29 @@ def handler(event, context):
     zip_file_relpath, content = create_python_awslambda(
         rule_runner,
         Address("src/python/foo/bar", target_name="lambda"),
-        expected_extra_log_lines=(
-            "    Handler: foo.bar.hello_world.handler",
-        ),
+        expected_extra_log_lines=("    Handler: lambdex_handler.handler",),
     )
     assert "src.python.foo.bar/lambda.zip" == zip_file_relpath
 
     zipfile = ZipFile(BytesIO(content))
     names = set(zipfile.namelist())
     assert "mureq/__init__.py" in names
     assert "foo/bar/hello_world.py" in names
+    assert (
+        zipfile.read("lambdex_handler.py") == b"from foo.bar.hello_world import handler as handler"
+    )
 
     zip_file_relpath, content = create_python_awslambda(
         rule_runner,
         Address("src/python/foo/bar", target_name="slimlambda"),
-        expected_extra_log_lines=(
-            "    Handler: foo.bar.hello_world.handler",
-        ),
+        expected_extra_log_lines=("    Handler: lambdex_handler.handler",),
     )
     assert "src.python.foo.bar/slimlambda.zip" == zip_file_relpath
 
     zipfile = ZipFile(BytesIO(content))
     names = set(zipfile.namelist())
     assert "mureq/__init__.py" not in names
     assert "foo/bar/hello_world.py" in names
+    assert (
+        zipfile.read("lambdex_handler.py") == b"from foo.bar.hello_world import handler as handler"
+    )

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

@@ -83,6 +83,14 @@ async def package_python_google_cloud_function(
             layout=layout,
             output_path=field_set.output_path,
             include_requirements=True,
+            # GCP requires "Your main file must be named main.py"
+            # https://cloud.google.com/functions/docs/writing#directory-structure-python
+            # setting a `GOOGLE_FUNCTION_SOURCE` Google Cloud build environment variable; e.g.:
+            # `gcloud functions deploy {--build-env-vars-file,--set-build-env-vars}`, but it's non-trivial
+            # to do this right or with intended effect) and the handler name you configure GCF with is just
+            # the unqualified function name, which we log here.
+            reexported_handler_module="main",
+            log_only_reexported_handler_func=True,
         ),
     )
 

src/python/pants/backend/google_cloud_function/python/rules_test.py

@@ -276,13 +276,12 @@ def handler(event, context):
     zip_file_relpath, content = create_python_google_cloud_function(
         rule_runner,
         Address("src/python/foo/bar", target_name="gcf"),
-        expected_extra_log_lines=(
-            "    Handler: foo.bar.hello_world.handler",
-        ),
+        expected_extra_log_lines=("    Handler: handler",),
     )
     assert "src.python.foo.bar/gcf.zip" == zip_file_relpath
 
     zipfile = ZipFile(BytesIO(content))
     names = set(zipfile.namelist())
     assert "mureq/__init__.py" in names
     assert "foo/bar/hello_world.py" in names
+    assert zipfile.read("main.py") == b"from foo.bar.hello_world import handler as handler"

src/python/pants/backend/python/util_rules/faas.py

@@ -45,7 +45,14 @@
 from pants.core.goals.package import BuiltPackage, BuiltPackageArtifact, OutputPathField
 from pants.core.target_types import FileSourceField
 from pants.engine.addresses import Address, UnparsedAddressInputs
-from pants.engine.fs import GlobMatchErrorBehavior, PathGlobs, Paths
+from pants.engine.fs import (
+    CreateDigest,
+    Digest,
+    FileContent,
+    GlobMatchErrorBehavior,
+    PathGlobs,
+    Paths,
+)
 from pants.engine.platform import Platform
 from pants.engine.process import ProcessResult
 from pants.engine.rules import Get, MultiGet, collect_rules, rule
@@ -450,6 +457,9 @@ class BuildPythonFaaSRequest:
 
     include_requirements: bool
 
+    reexported_handler_module: str
+    log_only_reexported_handler_func: bool = False
+
 
 @rule
 async def build_python_faas(
@@ -466,12 +476,27 @@ async def build_python_faas(
         "--resolve-local-platforms",
     )
 
-    complete_platforms = await Get(
-        CompletePlatforms, PythonFaaSCompletePlatforms, request.complete_platforms
+    complete_platforms, handler = await MultiGet(
+        Get(CompletePlatforms, PythonFaaSCompletePlatforms, request.complete_platforms),
+        Get(ResolvedPythonFaaSHandler, ResolvePythonFaaSHandlerRequest(request.handler)),
     )
 
     # TODO: improve diagnostics if there's more than one platform/complete_platform
 
+    # synthesise a source file that gives a fixed handler path, no matter what the entry point is:
+    # some platforms require a certain name (e.g. GCF), and even on others, giving a fixed name
+    # means users don't need to duplicate the entry_point config in both the pants BUILD file and
+    # infrastructure definitions (the latter can always use the same names, for every lambda).
+    reexported_handler_file = f"{request.reexported_handler_module}.py"
+    reexported_handler_func = "handler"
+    reexported_handler_content = (
+        f"from {handler.module} import {handler.func} as {reexported_handler_func}"
+    )
+    additional_sources = await Get(
+        Digest,
+        CreateDigest([FileContent(reexported_handler_file, reexported_handler_content.encode())]),
+    )
+
     repository_filename = "faas_repository.pex"
     pex_request = PexFromTargetsRequest(
         addresses=[request.address],
@@ -483,12 +508,10 @@ async def build_python_faas(
         layout=PexLayout.PACKED,
         additional_args=additional_pex_args,
         additional_lockfile_args=additional_pex_args,
+        additional_sources=additional_sources,
     )
 
-    pex_result, handler = await MultiGet(
-        Get(Pex, PexFromTargetsRequest, pex_request),
-        Get(ResolvedPythonFaaSHandler, ResolvePythonFaaSHandlerRequest(request.handler)),
-    )
+    pex_result = await Get(Pex, PexFromTargetsRequest, pex_request)
 
     output_filename = request.output_path.value_or_default(file_ending="zip")
 
@@ -504,11 +527,14 @@ async def build_python_faas(
         ),
     )
 
+    if request.log_only_reexported_handler_func:
+        handler_text = reexported_handler_func
+    else:
+        handler_text = f"{request.reexported_handler_module}.{reexported_handler_func}"
+
     artifact = BuiltPackageArtifact(
         output_filename,
-        extra_log_lines=(
-            f"    Handler: {handler.module}.{handler.func}",
-        ),
+        extra_log_lines=(f"    Handler: {handler_text}",),
     )
     return BuiltPackage(digest=result.digest, artifacts=(artifact,))