Add support for packaging type stubs in pure Rust project layout

Changelog.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Add PEP 656 musllinux support in [#543](https://github.com/PyO3/maturin/pull/543)
 * `--manylinux` is now called `--compatibility` and supports musllinux
 * The pure rust install layout changed from just the shared library to a python module that reexports the shared library. This should have now observable consequences for users of the created wheel expect that `my_project.my_project` is now also importable (and equal to just `my_project`)
+* Add support for packaging type stubs in pure Rust project layout in [#567](https://github.com/PyO3/maturin/pull/567)
 
 ## 0.10.6 - 2021-05-21
 

src/build_context.rs

@@ -56,7 +56,12 @@ pub enum ProjectLayout {
     /// A rust crate compiled into a shared library with only some glue python for cffi
     ///
     /// Contains the the rust extension name
-    PureRust(String),
+    PureRust {
+        /// Contains the canonicialized (i.e. absolute) path to the rust part of the project
+        rust_module: PathBuf,
+        /// rust extension name
+        extension_name: String,
+    },
     /// A python package that is extended by a native rust module.
     Mixed {
         /// Contains the canonicialized (i.e. absolute) path to the python part of the project
@@ -73,18 +78,19 @@ impl ProjectLayout {
     pub fn determine(project_root: impl AsRef<Path>, module_name: &str) -> Result<ProjectLayout> {
         // A dot in the module name means the extension module goes into the module folder specified by the path
         let parts: Vec<&str> = module_name.split('.').collect();
+        let project_root = project_root.as_ref();
         let (python_module, rust_module, extension_name) = if parts.len() > 1 {
-            let mut rust_module = project_root.as_ref().to_path_buf();
+            let mut rust_module = project_root.to_path_buf();
             rust_module.extend(&parts[0..parts.len() - 1]);
             (
-                project_root.as_ref().join(parts[0]),
+                project_root.join(parts[0]),
                 rust_module,
                 parts[parts.len() - 1].to_string(),
             )
         } else {
             (
-                project_root.as_ref().join(module_name),
-                project_root.as_ref().join(module_name),
+                project_root.join(module_name),
+                project_root.join(module_name),
                 module_name.to_string(),
             )
         };
@@ -101,13 +107,18 @@ impl ProjectLayout {
                 extension_name,
             })
         } else {
-            Ok(ProjectLayout::PureRust(extension_name))
+            Ok(ProjectLayout::PureRust {
+                rust_module: project_root.to_path_buf(),
+                extension_name,
+            })
         }
     }
 
     pub fn extension_name(&self) -> &str {
         match *self {
-            ProjectLayout::PureRust(ref name) => name,
+            ProjectLayout::PureRust {
+                ref extension_name, ..
+            } => extension_name,
             ProjectLayout::Mixed {
                 ref extension_name, ..
             } => extension_name,
@@ -435,7 +446,7 @@ impl BuildContext {
                 write_python_part(&mut builder, python_module, extension_name)
                     .context("Failed to add the python module to the package")?;
             }
-            ProjectLayout::PureRust(_) => {}
+            ProjectLayout::PureRust { .. } => {}
         }
 
         // I wouldn't know of any case where this would be the wrong (and neither do

src/module_writer.rs

@@ -609,14 +609,23 @@ pub fn write_bindings_module(
             let relative = rust_module.strip_prefix(python_module.parent().unwrap())?;
             writer.add_file_with_permissions(relative.join(&so_filename), &artifact, 0o755)?;
         }
-        ProjectLayout::PureRust(_) => {
+        ProjectLayout::PureRust {
+            ref rust_module, ..
+        } => {
             let module = PathBuf::from(module_name);
             writer.add_directory(&module)?;
             // Reexport the shared library as if it were the top level module
             writer.add_bytes(
                 &module.join("__init__.py"),
                 format!("from .{} import *\n", module_name).as_bytes(),
             )?;
+            let type_stub = rust_module.join(format!("{}.pyi", module_name));
+            if type_stub.exists() {
+                writer.add_bytes(
+                    &module.join("__init__.pyi"),
+                    &fs_err::read(type_stub).context("Failed to read type stub file")?,
+                )?;
+            }
             writer.add_file_with_permissions(&module.join(so_filename), &artifact, 0o755)?;
         }
     }
@@ -663,11 +672,23 @@ pub fn write_cffi_module(
 
             let relative = rust_module.strip_prefix(python_module.parent().unwrap())?;
             module = relative.join(extension_name);
+            writer.add_directory(&module)?;
+        }
+        ProjectLayout::PureRust {
+            ref rust_module, ..
+        } => {
+            module = PathBuf::from(module_name);
+            writer.add_directory(&module)?;
+            let type_stub = rust_module.join(format!("{}.pyi", module_name));
+            if type_stub.exists() {
+                writer.add_bytes(
+                    &module.join("__init__.pyi"),
+                    &fs_err::read(type_stub).context("Failed to read type stub file")?,
+                )?;
+            }
         }
-        ProjectLayout::PureRust(_) => module = PathBuf::from(module_name),
     };
 
-    writer.add_directory(&module)?;
     writer.add_bytes(&module.join("__init__.py"), cffi_init_file().as_bytes())?;
     writer.add_bytes(&module.join("ffi.py"), cffi_declarations.as_bytes())?;
     writer.add_file_with_permissions(&module.join("native.so"), &artifact, 0o755)?;

test-crates/pyo3-pure/check_installed/check_installed.py

@@ -1,6 +1,12 @@
 #!/usr/bin/env python3
+import os
 
 import pyo3_pure
 
 assert pyo3_pure.DummyClass.get_42() == 42
+
+# Check type stub
+type_stub = os.path.join(os.path.dirname(pyo3_pure.__file__), "__init__.pyi")
+assert os.path.exists(type_stub)
+
 print("SUCCESS")

test-crates/pyo3-pure/pyo3_pure.pyi

@@ -0,0 +1,5 @@
+class DummyClass:
+    @staticmethod
+    def get_42(self) -> int: ...
+
+fourtytwo: int