Add support for python first src project layout

```
my-project
├── Readme.md
├── pyproject.toml
├── src
│   └── my_project
│       ├── __init__.py
│       └── bar.py
└── rust
    ├── Cargo.toml
    └── src
        └── lib.rs
```

Changelog.md

@@ -7,7 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
- * Initial support for shipping bin targets as wasm32-wasi binaries that are run through wasmtime in [#1107](https://github.com/PyO3/maturin/pull/1107). Note that wasmtime currently only support the five most popular platforms and that wasi binaries have restrictions when interacting with the host. Usage is by setting `--target wasm32-wasi`.
+ * Initial support for shipping bin targets as wasm32-wasi binaries that are run through wasmtime in [#1107](https://github.com/PyO3/maturin/pull/1107). 
+   Note that wasmtime currently only support the five most popular platforms and that wasi binaries have restrictions when interacting with the host.
+   Usage is by setting `--target wasm32-wasi`.
+ * Add support for python first `src` project layout in [#1185](https://github.com/PyO3/maturin/pull/1185)
 
 ## [0.13.6] - 2022-10-08
 

src/module_writer.rs

@@ -47,10 +47,6 @@ pub trait ModuleWriter {
 
     /// Copies the source file to the target path relative to the module base path
     fn add_file(&mut self, target: impl AsRef<Path>, source: impl AsRef<Path>) -> Result<()> {
-        let target = target.as_ref();
-        let source = source.as_ref();
-        debug!("Adding {} from {}", target.display(), source.display());
-
         self.add_file_with_permissions(target, source, 0o644)
     }
 
@@ -62,12 +58,16 @@ pub trait ModuleWriter {
         source: impl AsRef<Path>,
         permissions: u32,
     ) -> Result<()> {
-        let read_failed_context = format!("Failed to read {}", source.as_ref().display());
-        let mut file = File::open(source.as_ref()).context(read_failed_context.clone())?;
+        let target = target.as_ref();
+        let source = source.as_ref();
+        debug!("Adding {} from {}", target.display(), source.display());
+
+        let read_failed_context = format!("Failed to read {}", source.display());
+        let mut file = File::open(source).context(read_failed_context.clone())?;
         let mut buffer = Vec::new();
         file.read_to_end(&mut buffer).context(read_failed_context)?;
-        self.add_bytes_with_permissions(target.as_ref(), &buffer, permissions)
-            .context(format!("Failed to write to {}", target.as_ref().display()))?;
+        self.add_bytes_with_permissions(target, &buffer, permissions)
+            .context(format!("Failed to write to {}", target.display()))?;
         Ok(())
     }
 }
@@ -640,11 +640,6 @@ pub fn write_bindings_module(
     };
 
     if let Some(python_module) = &project_layout.python_module {
-        if !editable {
-            write_python_part(writer, python_module)
-                .context("Failed to add the python module to the package")?;
-        }
-
         if editable {
             let target = project_layout.rust_module.join(&so_filename);
             // Remove existing so file to avoid triggering SIGSEV in running process
@@ -658,9 +653,10 @@ pub fn write_bindings_module(
                 artifact.display(),
                 target.display()
             ))?;
-        }
+        } else {
+            write_python_part(writer, python_module)
+                .context("Failed to add the python module to the package")?;
 
-        if !editable {
             let relative = project_layout
                 .rust_module
                 .strip_prefix(python_module.parent().unwrap())?;

src/project_layout.rs

@@ -63,6 +63,10 @@ impl ProjectResolver {
                 manifest_file.display()
             );
         }
+
+        // Set Cargo manifest path
+        cargo_options.manifest_path = Some(manifest_file.clone());
+
         let cargo_toml = CargoToml::from_path(&manifest_file)?;
         cargo_toml.warn_deprecated_python_metadata();
 
@@ -123,7 +127,18 @@ impl ProjectResolver {
             Some(py_src) => py_src.to_path_buf(),
             None => match extra_metadata.python_source.as_ref() {
                 Some(py_src) => manifest_dir.join(py_src),
-                None => project_root.to_path_buf(),
+                None => match pyproject.and_then(|x| x.project_name()) {
+                    Some(project_name) => {
+                        // Detect src layout
+                        let import_name = project_name.replace('-', "_");
+                        if project_root.join("src").join(import_name).is_dir() {
+                            project_root.join("src")
+                        } else {
+                            project_root.to_path_buf()
+                        }
+                    }
+                    None => project_root.to_path_buf(),
+                },
             },
         };
         let data = match pyproject.and_then(|x| x.data()) {
@@ -166,8 +181,10 @@ impl ProjectResolver {
         // use command line argument if specified
         if let Some(path) = cargo_manifest_path {
             let workspace_root = Self::resolve_cargo_metadata(&path, cargo_options)?.workspace_root;
+            let workspace_parent = workspace_root.parent().unwrap_or(&workspace_root);
             for parent in fs::canonicalize(&path)?.ancestors().skip(1) {
-                if !parent.starts_with(&workspace_root) {
+                // Allow looking outside to the parent directory of Cargo workspace root
+                if !dunce::simplified(parent).starts_with(&workspace_parent) {
                     break;
                 }
                 let pyproject_file = parent.join(PYPROJECT_TOML);
@@ -196,6 +213,33 @@ impl ProjectResolver {
                     bail!("Cargo.toml can not be placed outside of the directory containing pyproject.toml");
                 }
                 return Ok((path.to_path_buf(), pyproject_file));
+            } else {
+                // Detect src layout:
+                //
+                // my-project
+                // ├── Readme.md
+                // ├── pyproject.toml
+                // ├── src
+                // │   └── my_project
+                // │       ├── __init__.py
+                // │       └── bar.py
+                // └── rust
+                //     ├── Cargo.toml
+                //     └── src
+                //         └── lib.rs
+                let path = current_dir.join("rust").join("Cargo.toml");
+                if path.exists() {
+                    if pyproject.python_source().is_some() {
+                        // python source directory is specified in pyproject.toml
+                        return Ok((path, pyproject_file));
+                    } else if let Some(project_name) = pyproject.project_name() {
+                        // Check if python source directory in `src/<project_name>`
+                        let import_name = project_name.replace('-', "_");
+                        if current_dir.join("src").join(import_name).is_dir() {
+                            return Ok((path, pyproject_file));
+                        }
+                    }
+                }
             }
         }
         // check Cargo.toml in current directory

src/pyproject_toml.rs

@@ -86,6 +86,11 @@ impl PyProjectToml {
         Ok(pyproject)
     }
 
+    /// Returns the value of `[project.name]` in pyproject.toml
+    pub fn project_name(&self) -> Option<&str> {
+        self.project.as_ref().map(|project| project.name.as_str())
+    }
+
     /// Returns the values of `[tool.maturin]` in pyproject.toml
     #[inline]
     pub fn maturin(&self) -> Option<&ToolMaturin> {

test-crates/pyo3-mixed-src/README.md

@@ -0,0 +1,14 @@
+# pyo3-mixed src layout
+
+A package for testing maturin with a src layout mixed pyo3/python project.
+
+## Usage
+
+```bash
+pip install .
+```
+
+```python
+import pyo3_mixed_src
+assert pyo3_mixed_src.get_42() == 42
+```

test-crates/pyo3-mixed-src/check_installed/check_installed.py

@@ -0,0 +1,7 @@
+#!/usr/bin/env python3
+
+import pyo3_mixed_src as pyo3_mixed
+
+assert pyo3_mixed.get_42() == 42
+
+print("SUCCESS")

test-crates/pyo3-mixed-src/pyproject.toml

@@ -0,0 +1,14 @@
+[build-system]
+requires = ["maturin>=0.13,<0.14"]
+build-backend = "maturin"
+
+[project]
+name = "pyo3-mixed-src"
+classifiers = [
+    "Programming Language :: Python",
+    "Programming Language :: Rust"
+]
+requires-python = ">=3.7"
+
+[project.scripts]
+get_42 = "pyo3_mixed_src:get_42"