Detect imports in src layouts by default

CONTRIBUTING.md

@@ -911,9 +911,5 @@ There are three ways in which an import can be categorized as "first-party":
     the `src` setting and, for each directory, check for the existence of a subdirectory `foo` or a
     file `foo.py`.
 
-By default, `src` is set to the project root. In the above example, we'd want to set
-`src = ["./src"]` to ensure that we locate `./my_project/src/foo` and thus categorize `import foo`
-as first-party in `baz.py`. In practice, for this limited example, setting `src = ["./src"]` is
-unnecessary, as all imports within `./my_project/src/foo` would be categorized as first-party via
-the same-package heuristic; but if your project contains multiple packages, you'll want to set `src`
-explicitly.
+By default, `src` is set to the project root, along with `"src"` subdirectory in the project root.
+This ensures that Ruff supports both flat and "src" layouts out of the box

crates/ruff_workspace/src/configuration.rs

@@ -271,7 +271,6 @@ impl Configuration {
                         .chain(lint.extend_per_file_ignores)
                         .collect(),
                 )?,
-
                 fix_safety: FixSafetyTable::from_rule_selectors(
                     &lint.extend_safe_fixes,
                     &lint.extend_unsafe_fixes,
@@ -280,8 +279,9 @@ impl Configuration {
                         require_explicit: false,
                     },
                 ),
-
-                src: self.src.unwrap_or_else(|| vec![project_root.to_path_buf()]),
+                src: self
+                    .src
+                    .unwrap_or_else(|| vec![project_root.to_path_buf(), project_root.join("src")]),
                 explicit_preview_rules: lint.explicit_preview_rules.unwrap_or_default(),
 
                 task_tags: lint

crates/ruff_workspace/src/options.rs

@@ -323,7 +323,7 @@ pub struct Options {
     /// The directories to consider when resolving first- vs. third-party
     /// imports.
     ///
-    /// As an example: given a Python package structure like:
+    /// As an example, given a Python package structure like:
     ///
     /// ```text
     /// my_project
@@ -341,15 +341,17 @@ pub struct Options {
     ///
     /// When omitted, the `src` directory will typically default to the
     /// directory containing the nearest `pyproject.toml`, `ruff.toml`, or
-    /// `.ruff.toml` file (the "project root"), unless a configuration file
-    /// is explicitly provided (e.g., via the `--config` command-line flag).
+    /// `.ruff.toml` file (the "project root") along with a `"src"` subdirectory,
+    /// unless a configuration file is explicitly provided (e.g., via the
+    /// `--config` command-line flag). These defaults ensure that uv supports both
+    /// flat layouts and `src` layouts (as seen above) out of the box.
     ///
     /// This field supports globs. For example, if you have a series of Python
     /// packages in a `python_modules` directory, `src = ["python_modules/*"]`
-    /// would expand to incorporate all of the packages in that directory. User
-    /// home directory and environment variables will also be expanded.
+    /// would expand to incorporate all packages in that directory. User home
+    /// directory and environment variables will also be expanded.
     #[option(
-        default = r#"["."]"#,
+        default = r#"[".", "src"]"#,
         value_type = "list[str]",
         example = r#"
             # Allow imports relative to the "src" and "test" directories.