Default `src.root` to `['.', '<project_name>']` if the directory exists (#18141)

crates/ty/docs/configuration.md

@@ -164,7 +164,13 @@ typeshed = "/path/to/custom/typeshed"
 
 The root of the project, used for finding first-party modules.
 
-**Default value**: `[".", "./src"]`
+If left unspecified, ty will try to detect common project layouts and initialize `src.root` accordingly:
+
+* if a `./src` directory exists, include `.` and `./src` in the first party search path (src layout or flat)
+* if a `./<project-name>/<project-name>` directory exists, include `.` and `./<project-name>` in the first party search path
+* otherwise, default to `.` (flat layout)
+
+**Default value**: `null`
 
 **Type**: `str`
 

crates/ty_project/src/metadata.rs

@@ -244,7 +244,8 @@ impl ProjectMetadata {
     }
 
     pub fn to_program_settings(&self, system: &dyn System) -> ProgramSettings {
-        self.options.to_program_settings(self.root(), system)
+        self.options
+            .to_program_settings(self.root(), self.name(), system)
     }
 
     /// Combine the project options with the CLI options where the CLI options take precedence.
@@ -947,6 +948,87 @@ expected `.`, `]`
         Ok(())
     }
 
+    #[test]
+    fn no_src_root_src_layout() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_file_all(
+                root.join("src/main.py"),
+                r#"
+                print("Hello, world!")
+                "#,
+            )
+            .context("Failed to write file")?;
+
+        let metadata = ProjectMetadata::discover(&root, &system)?;
+        let settings = metadata
+            .options
+            .to_program_settings(&root, "my_package", &system);
+
+        assert_eq!(
+            settings.search_paths.src_roots,
+            vec![root.clone(), root.join("src")]
+        );
+
+        Ok(())
+    }
+
+    #[test]
+    fn no_src_root_package_layout() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_file_all(
+                root.join("psycopg/psycopg/main.py"),
+                r#"
+                print("Hello, world!")
+                "#,
+            )
+            .context("Failed to write file")?;
+
+        let metadata = ProjectMetadata::discover(&root, &system)?;
+        let settings = metadata
+            .options
+            .to_program_settings(&root, "psycopg", &system);
+
+        assert_eq!(
+            settings.search_paths.src_roots,
+            vec![root.clone(), root.join("psycopg")]
+        );
+
+        Ok(())
+    }
+
+    #[test]
+    fn no_src_root_flat_layout() -> anyhow::Result<()> {
+        let system = TestSystem::default();
+        let root = SystemPathBuf::from("/app");
+
+        system
+            .memory_file_system()
+            .write_file_all(
+                root.join("my_package/main.py"),
+                r#"
+                print("Hello, world!")
+                "#,
+            )
+            .context("Failed to write file")?;
+
+        let metadata = ProjectMetadata::discover(&root, &system)?;
+        let settings = metadata
+            .options
+            .to_program_settings(&root, "my_package", &system);
+
+        assert_eq!(settings.search_paths.src_roots, vec![root]);
+
+        Ok(())
+    }
+
     #[track_caller]
     fn assert_error_eq(error: &ProjectDiscoveryError, message: &str) {
         assert_eq!(error.to_string().replace('\\', "/"), message);

crates/ty_project/src/metadata/options.rs

@@ -87,6 +87,7 @@ impl Options {
     pub(crate) fn to_program_settings(
         &self,
         project_root: &SystemPath,
+        project_name: &str,
         system: &dyn System,
     ) -> ProgramSettings {
         let python_version = self
@@ -106,13 +107,14 @@ impl Options {
         ProgramSettings {
             python_version,
             python_platform,
-            search_paths: self.to_search_path_settings(project_root, system),
+            search_paths: self.to_search_path_settings(project_root, project_name, system),
         }
     }
 
     fn to_search_path_settings(
         &self,
         project_root: &SystemPath,
+        project_name: &str,
         system: &dyn System,
     ) -> SearchPathSettings {
         let src_roots = if let Some(src_root) = self.src.as_ref().and_then(|src| src.root.as_ref())
@@ -121,10 +123,24 @@ impl Options {
         } else {
             let src = project_root.join("src");
 
-            // Default to `src` and the project root if `src` exists and the root hasn't been specified.
             if system.is_directory(&src) {
+                // Default to `src` and the project root if `src` exists and the root hasn't been specified.
+                // This corresponds to the `src-layout`
+                tracing::debug!(
+                    "Including `./src` in `src.root` because a `./src` directory exists"
+                );
                 vec![project_root.to_path_buf(), src]
+            } else if system.is_directory(&project_root.join(project_name).join(project_name)) {
+                // `src-layout` but when the folder isn't called `src` but has the same name as the project.
+                // For example, the "src" folder for `psycopg` is called `psycopg` and the python files are in `psycopg/psycopg/_adapters_map.py`
+                tracing::debug!(
+                    "Including `./{project_name}` in `src.root` because a `./{project_name}/{project_name}` directory exists"
+                );
+
+                vec![project_root.to_path_buf(), project_root.join(project_name)]
             } else {
+                // Default to a [flat project structure](https://packaging.python.org/en/latest/discussions/src-layout-vs-flat-layout/).
+                tracing::debug!("Defaulting `src.root` to `.`");
                 vec![project_root.to_path_buf()]
             }
         };
@@ -353,9 +369,15 @@ pub struct EnvironmentOptions {
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct SrcOptions {
     /// The root of the project, used for finding first-party modules.
+    ///
+    /// If left unspecified, ty will try to detect common project layouts and initialize `src.root` accordingly:
+    ///
+    /// * if a `./src` directory exists, include `.` and `./src` in the first party search path (src layout or flat)
+    /// * if a `./<project-name>/<project-name>` directory exists, include `.` and `./<project-name>` in the first party search path
+    /// * otherwise, default to `.` (flat layout)
     #[serde(skip_serializing_if = "Option::is_none")]
     #[option(
-        default = r#"[".", "./src"]"#,
+        default = r#"null"#,
         value_type = "str",
         example = r#"
             root = "./app"

ty.schema.json

@@ -849,7 +849,7 @@
       "type": "object",
       "properties": {
         "root": {
-          "description": "The root of the project, used for finding first-party modules.",
+          "description": "The root of the project, used for finding first-party modules.\n\nIf left unspecified, ty will try to detect common project layouts and initialize `src.root` accordingly:\n\n* if a `./src` directory exists, include `.` and `./src` in the first party search path (src layout or flat) * if a `./<project-name>/<project-name>` directory exists, include `.` and `./<project-name>` in the first party search path * otherwise, default to `.` (flat layout)",
           "type": [
             "string",
             "null"