Speed up mypy startup by avoiding imports (#6127)

Move some imports that aren't always needed to functions bodies. This
speeds up mypy startup by up to 120ms on my laptop (when not compiled).
Tests are a bit faster as well.

Author: JukkaL

mypy/build.py

@@ -38,7 +38,8 @@
 from mypy.indirection import TypeIndirectionVisitor
 from mypy.errors import Errors, CompileError, report_internal_error
 from mypy.util import DecodeError, decode_python_encoding, is_sub_path
-from mypy.report import Reports
+if MYPY:
+    from mypy.report import Reports  # Avoid unconditional slow import
 from mypy import moduleinfo
 from mypy.fixup import fixup_module
 from mypy.modulefinder import BuildSource, compute_search_paths, FindModuleCache, SearchPaths
@@ -50,7 +51,6 @@
 from mypy.version import __version__
 from mypy.plugin import Plugin, ChainedPlugin, plugin_types
 from mypy.plugins.default import DefaultPlugin
-from mypy.server.deps import get_dependencies
 from mypy.fscache import FileSystemCache
 from mypy.metastore import MetadataStore, FilesystemMetadataStore, SqliteMetadataStore
 from mypy.typestate import TypeState, reset_global_state
@@ -182,7 +182,12 @@ def _build(sources: List[BuildSource],
 
     search_paths = compute_search_paths(sources, options, data_dir, alt_lib_path)
 
-    reports = Reports(data_dir, options.report_dirs)
+    reports = None
+    if options.report_dirs:
+        # Import lazily to avoid slowing down startup.
+        from mypy.report import Reports  # noqa
+        reports = Reports(data_dir, options.report_dirs)
+
     source_set = BuildSourceSet(sources)
     errors = Errors(options.show_error_context, options.show_column_numbers)
     plugin, snapshot = load_plugins(options, errors)
@@ -214,8 +219,9 @@ def _build(sources: List[BuildSource],
                     (time.time() - manager.start_time,
                      len(manager.modules),
                      manager.errors.num_messages()))
-        # Finish the HTML or XML reports even if CompileError was raised.
-        reports.finish()
+        if reports is not None:
+            # Finish the HTML or XML reports even if CompileError was raised.
+            reports.finish()
 
 
 def default_data_dir() -> str:
@@ -473,7 +479,7 @@ def __init__(self, data_dir: str,
                  search_paths: SearchPaths,
                  ignore_prefix: str,
                  source_set: BuildSourceSet,
-                 reports: Reports,
+                 reports: Optional['Reports'],
                  options: Options,
                  version_id: str,
                  plugin: Plugin,
@@ -504,10 +510,11 @@ def __init__(self, data_dir: str,
         self.stale_modules = set()  # type: Set[str]
         self.rechecked_modules = set()  # type: Set[str]
         self.flush_errors = flush_errors
+        has_reporters = reports is not None and reports.reporters
         self.cache_enabled = (options.incremental
                               and (not options.fine_grained_incremental
                                    or options.use_fine_grained_cache)
-                              and not reports.reporters)
+                              and not has_reporters)
         self.fscache = fscache
         self.find_module_cache = FindModuleCache(self.search_paths, self.fscache, self.options)
         if options.sqlite_cache:
@@ -679,7 +686,7 @@ def report_file(self,
                     file: MypyFile,
                     type_map: Dict[Expression, Type],
                     options: Options) -> None:
-        if self.source_set.is_source(file):
+        if self.reports is not None and self.source_set.is_source(file):
             self.reports.file(file, type_map, options)
 
     def stats_summary(self) -> Mapping[str, object]:
@@ -1845,6 +1852,7 @@ def compute_fine_grained_deps(self) -> None:
             # TODO: Not a reliable test, as we could have a package named typeshed.
             # TODO: Consider relaxing this -- maybe allow some typeshed changes to be tracked.
             return
+        from mypy.server.deps import get_dependencies  # Lazy import to speed up startup
         self.fine_grained_deps = get_dependencies(target=self.tree,
                                                   type_map=self.type_map(),
                                                   python_version=self.options.python_version,

mypy/defaults.py

@@ -10,3 +10,17 @@
 SHARED_CONFIG_FILES = ('setup.cfg',)  # type: Final
 USER_CONFIG_FILES = ('~/.mypy.ini',)  # type: Final
 CONFIG_FILES = (CONFIG_FILE,) + SHARED_CONFIG_FILES + USER_CONFIG_FILES  # type: Final
+
+# This must include all reporters defined in mypy.report. This is defined here
+# to make reporter names available without importing mypy.report -- this speeds
+# up startup.
+REPORTER_NAMES = ['linecount',
+                  'any-exprs',
+                  'linecoverage',
+                  'memory-xml',
+                  'cobertura-xml',
+                  'xml',
+                  'xslt-html',
+                  'xslt-txt',
+                  'html',
+                  'txt']  # type: Final

mypy/main.py

@@ -20,7 +20,6 @@
 from mypy.fscache import FileSystemCache
 from mypy.errors import CompileError
 from mypy.options import Options, BuildType, PER_MODULE_OPTIONS
-from mypy.report import reporter_classes
 
 from mypy.version import __version__
 
@@ -606,7 +605,7 @@ def add_invertible_flag(flag: str,
     report_group = parser.add_argument_group(
         title='Report generation',
         description='Generate a report in the specified format.')
-    for report_type in sorted(reporter_classes):
+    for report_type in sorted(defaults.REPORTER_NAMES):
         report_group.add_argument('--%s-report' % report_type.replace('_', '-'),
                                   metavar='DIR',
                                   dest='special-opts:%s_report' % report_type)
@@ -968,7 +967,7 @@ def parse_section(prefix: str, template: Options,
             if dv is None:
                 if key.endswith('_report'):
                     report_type = key[:-7].replace('_', '-')
-                    if report_type in reporter_classes:
+                    if report_type in defaults.REPORTER_NAMES:
                         report_dirs[report_type] = section[key]
                     else:
                         print("%s: Unrecognized report type: %s" % (prefix, key),

mypy/report.py

@@ -23,6 +23,7 @@
 from mypy.traverser import TraverserVisitor
 from mypy.types import Type, TypeOfAny
 from mypy.version import __version__
+from mypy.defaults import REPORTER_NAMES
 
 MYPY = False
 if MYPY:
@@ -749,3 +750,7 @@ def on_finish(self) -> None:
 
 alias_reporter('xslt-html', 'html')
 alias_reporter('xslt-txt', 'txt')
+
+# Reporter class names are defined twice to speed up mypy startup, as this
+# module is slow to import. Ensure that the two definitions match.
+assert set(reporter_classes) == set(REPORTER_NAMES)

mypy/util.py

@@ -1,11 +1,9 @@
 """Utility functions with no non-trivial dependencies."""
-import inspect
 import os
 import pathlib
 import re
 import subprocess
 import sys
-from xml.sax.saxutils import escape
 from typing import TypeVar, List, Tuple, Optional, Dict, Sequence
 
 MYPY = False
@@ -143,7 +141,7 @@ def try_find_python2_interpreter() -> Optional[str]:
 
 
 def write_junit_xml(dt: float, serious: bool, messages: List[str], path: str) -> None:
-    """XXX"""
+    from xml.sax.saxutils import escape
     if not messages and not serious:
         xml = PASS_TEMPLATE.format(time=dt)
     elif not serious:
@@ -205,6 +203,7 @@ def correct_relative_import(cur_mod_id: str,
 
 
 def get_class_descriptors(cls: 'Type[object]') -> Sequence[str]:
+    import inspect  # Lazy import for minor startup speed win
     # Maintain a cache of type -> attributes defined by descriptors in the class
     # (that is, attributes from __slots__ and C extension classes)
     if cls not in fields_cache: