Improve missing module error for subdirectories (#8927)

Fixes #7405

Author: ethan-leba

mypy/modulefinder.py

@@ -49,10 +49,18 @@ class ModuleNotFoundReason(Enum):
     # corresponding *-stubs package.
     FOUND_WITHOUT_TYPE_HINTS = 1
 
+    # The module was not found in the current working directory, but
+    # was able to be found in the parent directory.
+    WRONG_WORKING_DIRECTORY = 2
+
     def error_message_templates(self) -> Tuple[str, str]:
         if self is ModuleNotFoundReason.NOT_FOUND:
             msg = "Cannot find implementation or library stub for module named '{}'"
             note = "See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports"
+        elif self is ModuleNotFoundReason.WRONG_WORKING_DIRECTORY:
+            msg = "Cannot find implementation or library stub for module named '{}'"
+            note = ("You may be running mypy in a subpackage, "
+                    "mypy should be run on the package root")
         elif self is ModuleNotFoundReason.FOUND_WITHOUT_TYPE_HINTS:
             msg = "Skipping analyzing '{}': found module but no type hints or library stubs"
             note = "See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports"
@@ -166,6 +174,9 @@ def find_module(self, id: str) -> ModuleSearchResult:
         """Return the path of the module source file or why it wasn't found."""
         if id not in self.results:
             self.results[id] = self._find_module(id)
+            if (self.results[id] is ModuleNotFoundReason.NOT_FOUND
+                    and self._can_find_module_in_parent_dir(id)):
+                self.results[id] = ModuleNotFoundReason.WRONG_WORKING_DIRECTORY
         return self.results[id]
 
     def _find_module_non_stub_helper(self, components: List[str],
@@ -192,6 +203,20 @@ def _update_ns_ancestors(self, components: List[str], match: Tuple[str, bool]) -
                 self.ns_ancestors[pkg_id] = path
             path = os.path.dirname(path)
 
+    def _can_find_module_in_parent_dir(self, id: str) -> bool:
+        """Test if a module can be found by checking the parent directories
+        of the current working directory.
+        """
+        working_dir = os.getcwd()
+        parent_search = FindModuleCache(SearchPaths((), (), (), ()))
+        while any(file.endswith(("__init__.py", "__init__.pyi"))
+                  for file in os.listdir(working_dir)):
+            working_dir = os.path.dirname(working_dir)
+            parent_search.search_paths = SearchPaths((working_dir,), (), (), ())
+            if not isinstance(parent_search._find_module(id), ModuleNotFoundReason):
+                return True
+        return False
+
     def _find_module(self, id: str) -> ModuleSearchResult:
         fscache = self.fscache
 

mypy/test/testcmdline.py

@@ -10,6 +10,7 @@
 import sys
 
 from typing import List
+from typing import Optional
 
 from mypy.test.config import test_temp_dir, PREFIX
 from mypy.test.data import DataDrivenTestCase, DataSuite
@@ -45,6 +46,7 @@ def test_python_cmdline(testcase: DataDrivenTestCase, step: int) -> None:
         for s in testcase.input:
             file.write('{}\n'.format(s))
     args = parse_args(testcase.input[0])
+    custom_cwd = parse_cwd(testcase.input[1]) if len(testcase.input) > 1 else None
     args.append('--show-traceback')
     args.append('--no-site-packages')
     if '--error-summary' not in args:
@@ -56,7 +58,10 @@ def test_python_cmdline(testcase: DataDrivenTestCase, step: int) -> None:
     process = subprocess.Popen(fixed + args,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE,
-                               cwd=test_temp_dir,
+                               cwd=os.path.join(
+                                   test_temp_dir,
+                                   custom_cwd or ""
+                                   ),
                                env=env)
     outb, errb = process.communicate()
     result = process.returncode
@@ -112,3 +117,18 @@ def parse_args(line: str) -> List[str]:
     if not m:
         return []  # No args; mypy will spit out an error.
     return m.group(1).split()
+
+
+def parse_cwd(line: str) -> Optional[str]:
+    """Parse the second line of the program for the command line.
+
+    This should have the form
+
+      # cwd: <directory>
+
+    For example:
+
+      # cwd: main/subdir
+    """
+    m = re.match('# cwd: (.*)$', line)
+    return m.group(1) if m else None

test-data/unit/cmdline.test

@@ -486,6 +486,37 @@ ignore_missing_imports = True
 [out]
 main.py:2: note: Revealed type is 'Any'
 
+
+[case testFailedImportOnWrongCWD]
+# cmd: mypy main.py
+# cwd: main/subdir1/subdir2
+[file main/subdir1/subdir2/main.py]
+import parent
+import grandparent
+import missing
+[file main/subdir1/subdir2/__init__.py]
+[file main/subdir1/parent.py]
+[file main/subdir1/__init__.py]
+[file main/grandparent.py]
+[file main/__init__.py]
+[out]
+main.py:1: error: Cannot find implementation or library stub for module named 'parent'
+main.py:1: note: You may be running mypy in a subpackage, mypy should be run on the package root
+main.py:2: error: Cannot find implementation or library stub for module named 'grandparent'
+main.py:3: error: Cannot find implementation or library stub for module named 'missing'
+main.py:3: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
+
+[case testImportInParentButNoInit]
+# cmd: mypy main.py
+# cwd: main/not_a_package
+[file main/not_a_package/main.py]
+import needs_init
+[file main/needs_init.py]
+[file main/__init__.py]
+[out]
+main.py:1: error: Cannot find implementation or library stub for module named 'needs_init'
+main.py:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
+
 [case testConfigNoErrorForUnknownXFlagInSubsection]
 # cmd: mypy -c pass
 [file mypy.ini]