Provide an API for passing plugins to the Coverage constructor

coverage/control.py

@@ -43,14 +43,14 @@
 from coverage.misc import DefaultValue, ensure_dir_for_file, isolate_module
 from coverage.multiproc import patch_multiprocessing
 from coverage.plugin import FileReporter
-from coverage.plugin_support import Plugins
+from coverage.plugin_support import Plugins, TCoverageInit
 from coverage.python import PythonFileReporter
 from coverage.report import SummaryReporter
 from coverage.report_core import render_report
 from coverage.results import Analysis, analysis_from_file_reporter
 from coverage.types import (
     FilePath, TConfigurable, TConfigSectionIn, TConfigValueIn, TConfigValueOut,
-    TFileDisposition, TLineNo, TMorf,
+    TFileDisposition, TLineNo, TMorf
 )
 from coverage.xmlreport import XmlReporter
 
@@ -138,6 +138,7 @@ def __init__(                       # pylint: disable=too-many-arguments
         check_preimported: bool = False,
         context: str | None = None,
         messages: bool = False,
+        plugins: Iterable[TCoverageInit] | None = None,
     ) -> None:
         """
         Many of these arguments duplicate and override values that can be
@@ -211,6 +212,10 @@ def __init__(                       # pylint: disable=too-many-arguments
         If `messages` is true, some messages will be printed to stdout
         indicating what is happening.
 
+        If `plugins` are passed, they are an iterable of functions with the
+        `coverage_init` signature. When they are provided, they will override
+        the plugins found in the coverage configuration file.
+
         .. versionadded:: 4.0
             The `concurrency` parameter.
 
@@ -260,6 +265,7 @@ def __init__(                       # pylint: disable=too-many-arguments
         self._debug: DebugControl = NoDebugging()
         self._inorout: InOrOut | None = None
         self._plugins: Plugins = Plugins()
+        self._plugin_override = plugins
         self._data: CoverageData | None = None
         self._core: Core | None = None
         self._collector: Collector | None = None
@@ -340,7 +346,12 @@ def _init(self) -> None:
             self._file_mapper = relative_filename
 
         # Load plugins
-        self._plugins = Plugins.load_plugins(self.config.plugins, self.config, self._debug)
+        self._plugins = Plugins.load_plugins(
+            self.config.plugins,
+            self.config,
+            self._debug,
+            plugin_override=self._plugin_override
+        )
 
         # Run configuring plugins.
         for plugin in self._plugins.configurers:

coverage/plugin_support.py

@@ -11,13 +11,14 @@
 
 from types import FrameType
 from typing import Any
+from typing import Callable
 from collections.abc import Iterable, Iterator
 
 from coverage.exceptions import PluginError
 from coverage.misc import isolate_module
 from coverage.plugin import CoveragePlugin, FileTracer, FileReporter
 from coverage.types import (
-    TArc, TConfigurable, TDebugCtl, TLineNo, TPluginConfig, TSourceTokenLines,
+    TArc, TConfigurable, TDebugCtl, TLineNo, TPluginConfig, TSourceTokenLines, TConfigSectionOut
 )
 
 os = isolate_module(os)
@@ -42,6 +43,7 @@ def load_plugins(
         modules: Iterable[str],
         config: TPluginConfig,
         debug: TDebugCtl | None = None,
+        plugin_override: Iterable[TCoverageInit] | None = None,
     ) -> Plugins:
         """Load plugins from `modules`.
 
@@ -51,19 +53,23 @@ def load_plugins(
         plugins = cls()
         plugins.debug = debug
 
-        for module in modules:
-            plugins.current_module = module
-            __import__(module)
-            mod = sys.modules[module]
+        if plugin_override is not None:
+            for override in plugin_override:
+                override(plugins, {})
+        else:
+            for module in modules:
+                plugins.current_module = module
+                __import__(module)
+                mod = sys.modules[module]
 
-            coverage_init = getattr(mod, "coverage_init", None)
-            if not coverage_init:
-                raise PluginError(
-                    f"Plugin module {module!r} didn't define a coverage_init function",
-                )
+                coverage_init = getattr(mod, "coverage_init", None)
+                if not coverage_init:
+                    raise PluginError(
+                        f"Plugin module {module!r} didn't define a coverage_init function",
+                    )
 
-            options = config.get_plugin_options(module)
-            coverage_init(plugins, options)
+                options = config.get_plugin_options(module)
+                coverage_init(plugins, options)
 
         plugins.current_module = None
         return plugins
@@ -138,6 +144,9 @@ def get(self, plugin_name: str) -> CoveragePlugin:
         return self.names[plugin_name]
 
 
+TCoverageInit = Callable[[Plugins, TConfigSectionOut], None]
+
+
 class LabelledDebug:
     """A Debug writer, but with labels for prepending to the messages."""
 

tests/test_plugins.py

@@ -272,6 +272,21 @@ def coverage_init(reg, options):
         out = self.run_command("coverage html -q")  # sneak in a test of -q
         assert out == ""
 
+    def test_coverage_init_plugins(self) -> None:
+        called = False
+        def coverage_init(
+            reg: Plugins, # pylint: disable=unused-argument
+            options: TConfigSectionOut # pylint: disable=unused-argument
+        ) -> None:
+            nonlocal called
+            called = True
+
+        cov = coverage.Coverage(plugins=[coverage_init])
+        # Calls _init() and loads plugins
+        cov.sys_info()
+
+        assert called
+
 
 @pytest.mark.skipif(testenv.PLUGINS, reason="This core doesn't support plugins.")
 class PluginWarningOnPyTracerTest(CoverageTest):