Fail with an explicit error on PyPy

Author: ilevkivskyi

mypy-requirements.txt

@@ -4,4 +4,4 @@ typing_extensions>=4.6.0
 mypy_extensions>=1.0.0
 pathspec>=0.9.0
 tomli>=1.1.0; python_version<'3.11'
-librt>=0.6.2
+librt>=0.6.2; platform_python_implementation != 'PyPy'

mypy/build.py

@@ -40,7 +40,15 @@
     TypedDict,
 )
 
-from librt.internal import cache_version
+try:
+    from librt.internal import cache_version
+except ImportError:
+    print(
+        "Running mypy on PyPy is not supported yet."
+        "To type-check a PyPy library please run mypy on an equivalent CPython version,"
+        "see https://github.com/mypyc/librt/issues/16 for possible workarounds."
+    )
+    sys.exit(2)
 
 import mypy.semanal_main
 from mypy.cache import CACHE_VERSION, CacheMeta, ReadBuffer, WriteBuffer, write_json

pyproject.toml

@@ -9,7 +9,7 @@ requires = [
     "mypy_extensions>=1.0.0",
     "pathspec>=0.9.0",
     "tomli>=1.1.0; python_version<'3.11'",
-    "librt>=0.6.2",
+    "librt>=0.6.2; platform_python_implementation != 'PyPy'",
     # the following is from build-requirements.txt
     "types-psutil",
     "types-setuptools",
@@ -53,7 +53,7 @@ dependencies = [
   "mypy_extensions>=1.0.0",
   "pathspec>=0.9.0",
   "tomli>=1.1.0; python_version<'3.11'",
-  "librt>=0.6.2",
+  "librt>=0.6.2; platform_python_implementation != 'PyPy'",
 ]
 dynamic = ["version"]
 

test-requirements.txt

@@ -22,7 +22,7 @@ identify==2.6.15
     # via pre-commit
 iniconfig==2.1.0
     # via pytest
-librt==0.6.2
+librt==0.7.3 ; platform_python_implementation != 'PyPy'
     # via -r mypy-requirements.txt
 lxml==6.0.2 ; python_version < "3.15"
     # via -r test-requirements.in