Reduce size of JSON data in Mypy cache (#14808)

By default, Python outputs spaces after commas and colons when dumping
JSON data. This is normally fine, but when exporting large amounts of
JSON (such as cache info) it is more space efficient to export JSON
without whitespaces. To do this, simply pass `separators=(",", ":")` to
`json.dumps()`.

Although the space savings aren't massive, they do reduce the size of
the cache folder by a couple of megabytes:

| Method  | Size   |
|---------|--------|
| Current | 31.2MB |
| This PR | 29.3MB |

For comparison, the size of the cache folder with the `--sqlite-cache`
option is about 27.5MB.

mypy/build.py

@@ -919,7 +919,7 @@ def stats_summary(self) -> Mapping[str, object]:
 
 
 def deps_to_json(x: dict[str, set[str]]) -> str:
-    return json.dumps({k: list(v) for k, v in x.items()})
+    return json.dumps({k: list(v) for k, v in x.items()}, separators=(",", ":"))
 
 
 # File for storing metadata about all the fine-grained dependency caches
@@ -987,7 +987,7 @@ def write_deps_cache(
 
     meta = {"snapshot": meta_snapshot, "deps_meta": fg_deps_meta}
 
-    if not metastore.write(DEPS_META_FILE, json.dumps(meta)):
+    if not metastore.write(DEPS_META_FILE, json.dumps(meta, separators=(",", ":"))):
         manager.log(f"Error writing fine-grained deps meta JSON file {DEPS_META_FILE}")
         error = True
 
@@ -1055,7 +1055,8 @@ def generate_deps_for_cache(manager: BuildManager, graph: Graph) -> dict[str, di
 
 def write_plugins_snapshot(manager: BuildManager) -> None:
     """Write snapshot of versions and hashes of currently active plugins."""
-    if not manager.metastore.write(PLUGIN_SNAPSHOT_FILE, json.dumps(manager.plugins_snapshot)):
+    snapshot = json.dumps(manager.plugins_snapshot, separators=(",", ":"))
+    if not manager.metastore.write(PLUGIN_SNAPSHOT_FILE, snapshot):
         manager.errors.set_file(_cache_dir_prefix(manager.options), None, manager.options)
         manager.errors.report(0, 0, "Error writing plugins snapshot", blocker=True)
 
@@ -1487,7 +1488,7 @@ def validate_meta(
             if manager.options.debug_cache:
                 meta_str = json.dumps(meta_dict, indent=2, sort_keys=True)
             else:
-                meta_str = json.dumps(meta_dict)
+                meta_str = json.dumps(meta_dict, separators=(",", ":"))
             meta_json, _, _ = get_cache_names(id, path, manager.options)
             manager.log(
                 "Updating mtime for {}: file {}, meta {}, mtime {}".format(
@@ -1517,7 +1518,7 @@ def json_dumps(obj: Any, debug_cache: bool) -> str:
     if debug_cache:
         return json.dumps(obj, indent=2, sort_keys=True)
     else:
-        return json.dumps(obj, sort_keys=True)
+        return json.dumps(obj, sort_keys=True, separators=(",", ":"))
 
 
 def write_cache(
@@ -3639,4 +3640,4 @@ def write_undocumented_ref_info(state: State, metastore: MetadataStore, options:
     assert not ref_info_file.startswith(".")
 
     deps_json = get_undocumented_ref_info_json(state.tree)
-    metastore.write(ref_info_file, json.dumps(deps_json))
+    metastore.write(ref_info_file, json.dumps(deps_json, separators=(",", ":")))

mypyc/codegen/emitmodule.py

@@ -369,7 +369,7 @@ def write_cache(
             "src_hashes": hashes[group_map[id]],
         }
 
-        result.manager.metastore.write(newpath, json.dumps(ir_data))
+        result.manager.metastore.write(newpath, json.dumps(ir_data, separators=(",", ":")))
 
     result.manager.metastore.commit()