Review

Author: konstin

crates/uv-build-backend/src/lib.rs

@@ -56,16 +56,17 @@ pub enum Error {
     #[error("Failed to write RECORD file")]
     Csv(#[from] csv::Error),
     #[error(
-        "Expected a Python module for `{}` with an `__init__.py` at: `{}`",
-        module_name,
-        project_src.user_display()
+        "Expected a Python module directory at: `{}`",
+        _0.user_display()
     )]
-    MissingModule {
-        module_name: Identifier,
-        project_src: PathBuf,
-    },
+    MissingModule(PathBuf),
+    #[error(
+        "Expected an `__init__.py` at: `{}`",
+        _0.user_display()
+    )]
+    MissingInitPy(PathBuf),
     #[error(
-        "Expected a single Python module for `{}` with an `__init__.py`, found multiple:\n* `{}`",
+        "Expected an `__init__.py` at `{}`, found multiple:\n* `{}`",
         module_name,
         paths.iter().map(Simplified::user_display).join("`\n* `")
     )]

crates/uv-build-backend/src/wheel.rs

@@ -254,17 +254,25 @@ fn find_module_root(src_root: &Path, module_name: Identifier) -> Result<PathBuf,
     let normalized = module_name.to_string();
     let modules = fs_err::read_dir(src_root)?
         .filter_ok(|entry| {
-            entry.file_name().to_string_lossy().to_lowercase() == normalized
-                && entry.path().join("__init__.py").is_file()
+            entry
+                .file_name()
+                .to_str()
+                .is_some_and(|file_name| file_name.to_lowercase() == normalized)
         })
         .map_ok(|entry| entry.path())
         .collect::<Result<Vec<_>, _>>()?;
     match modules.as_slice() {
-        [] => Err(Error::MissingModule {
-            module_name,
-            project_src: src_root.to_path_buf(),
-        }),
-        [module_root] => Ok(module_root.clone()),
+        [] => {
+            // Show the normalized path in the error message, as representative example.
+            Err(Error::MissingModule(src_root.join(module_name.as_ref())))
+        }
+        [module_root] => {
+            if module_root.join("__init__.py").is_file() {
+                Ok(module_root.clone())
+            } else {
+                Err(Error::MissingInitPy(module_root.join("__init__.py")))
+            }
+        }
         multiple => {
             let mut paths = multiple.to_vec();
             paths.sort();

crates/uv/tests/it/build_backend.rs

@@ -458,14 +458,28 @@ fn build_module_name_normalization() -> Result<()> {
     uv_snapshot!(context
         .build_backend()
         .arg("build-wheel")
-        .arg(&wheel_dir), @r"
+        .arg(&wheel_dir), @r###"
     success: false
     exit_code: 2
     ----- stdout -----
 
     ----- stderr -----
-    error: Expected a Python module for `django_plugin` with an `__init__.py` at: `src`
-    ");
+    error: Expected a Python module directory at: `src/django_plugin`
+    "###);
+
+    fs_err::create_dir_all(context.temp_dir.join("src/Django_plugin"))?;
+    // Error case 2: A matching module, but no `__init__.py`.
+    uv_snapshot!(context
+        .build_backend()
+        .arg("build-wheel")
+        .arg(&wheel_dir), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Expected an `__init__.py` at: `src/Django_plugin/__init__.py`
+    "###);
 
     // Use `Django_plugin` instead of `django_plugin`
     context
@@ -507,7 +521,7 @@ fn build_module_name_normalization() -> Result<()> {
     ----- stderr -----
     ");
 
-    // Error case 2: Multiple modules a matching name.
+    // Error case 3: Multiple modules a matching name.
     // Requires a case-sensitive filesystem.
     #[cfg(target_os = "linux")]
     {