From 264715e1fdcc9e8df2bbdff1168b68725864c01b Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Wed, 19 Apr 2017 14:51:30 -0700
Subject: [PATCH] Always write the cache (unless cache_dir is /dev/null)
 (#3133)

---
 mypy/build.py | 59 ++++++++++++++++++++++++++++++---------------------
 1 file changed, 35 insertions(+), 24 deletions(-)

diff --git a/mypy/build.py b/mypy/build.py
index 682fa1e00398..5ab87ab323f0 100644
--- a/mypy/build.py
+++ b/mypy/build.py
@@ -860,8 +860,7 @@ def write_cache(id: str, path: str, tree: MypyFile,
 
     # Make sure directory for cache files exists
     parent = os.path.dirname(data_json)
-    if not os.path.isdir(parent):
-        os.makedirs(parent)
+    os.makedirs(parent, exist_ok=True)
     assert os.path.dirname(meta_json) == parent
 
     # Construct temp file names
@@ -877,6 +876,20 @@ def write_cache(id: str, path: str, tree: MypyFile,
         data_str = json.dumps(data, sort_keys=True)
     interface_hash = compute_hash(data_str)
 
+    # Obtain and set up metadata
+    try:
+        st = manager.get_stat(path)
+    except OSError as err:
+        manager.log("Cannot get stat for {}: {}".format(path, err))
+        # Remove apparently-invalid cache files.
+        for filename in [data_json, meta_json]:
+            try:
+                os.remove(filename)
+            except OSError:
+                pass
+        # Still return the interface hash we computed.
+        return interface_hash
+
     # Write data cache file, if applicable
     if old_interface_hash == interface_hash:
         # If the interface is unchanged, the cached data is guaranteed
@@ -891,8 +904,6 @@ def write_cache(id: str, path: str, tree: MypyFile,
         os.replace(data_json_tmp, data_json)
         manager.trace("Interface for {} has changed".format(id))
 
-    # Obtain and set up metadata
-    st = manager.get_stat(path)  # TODO: Handle errors
     mtime = st.st_mtime
     size = st.st_size
     options = manager.options.clone_for_module(id)
@@ -1524,26 +1535,26 @@ def valid_references(self) -> Set[str]:
         return valid_refs
 
     def write_cache(self) -> None:
-        ok = self.path and self.options.incremental
-        if ok:
-            if self.manager.options.quick_and_dirty:
-                is_errors = self.manager.errors.is_errors_for_file(self.path)
-            else:
-                is_errors = self.manager.errors.is_errors()
-            ok = not is_errors
-        if ok:
-            dep_prios = [self.priorities.get(dep, PRI_HIGH) for dep in self.dependencies]
-            new_interface_hash = write_cache(
-                self.id, self.path, self.tree,
-                list(self.dependencies), list(self.suppressed), list(self.child_modules),
-                dep_prios, self.interface_hash,
-                self.manager)
-            if new_interface_hash == self.interface_hash:
-                self.manager.log("Cached module {} has same interface".format(self.id))
-            else:
-                self.manager.log("Cached module {} has changed interface".format(self.id))
-                self.mark_interface_stale()
-                self.interface_hash = new_interface_hash
+        if not self.path or self.options.cache_dir == os.devnull:
+            return
+        if self.manager.options.quick_and_dirty:
+            is_errors = self.manager.errors.is_errors_for_file(self.path)
+        else:
+            is_errors = self.manager.errors.is_errors()
+        if is_errors:
+            return
+        dep_prios = [self.priorities.get(dep, PRI_HIGH) for dep in self.dependencies]
+        new_interface_hash = write_cache(
+            self.id, self.path, self.tree,
+            list(self.dependencies), list(self.suppressed), list(self.child_modules),
+            dep_prios, self.interface_hash,
+            self.manager)
+        if new_interface_hash == self.interface_hash:
+            self.manager.log("Cached module {} has same interface".format(self.id))
+        else:
+            self.manager.log("Cached module {} has changed interface".format(self.id))
+            self.mark_interface_stale()
+            self.interface_hash = new_interface_hash
 
 
 def dispatch(sources: List[BuildSource], manager: BuildManager) -> Graph: