Add support for Fluent message attributes

CHANGELOG.md

@@ -7,6 +7,8 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+- Add support for Fluent message attributes via dot notation (e.g., `bundle.get_translation("message.attribute")`).
+
 ## [0.1.0a8] - 2025-10-01
 
 - Annotate `ftl` file source code when reporting parse errors to allow ergonomic debugging.

src/lib.rs

@@ -77,14 +77,29 @@ mod rustfluent {
         ) -> PyResult<String> {
             self.bundle.set_use_isolating(use_isolating);
 
-            let msg = self
-                .bundle
-                .get_message(identifier)
-                .ok_or_else(|| (PyValueError::new_err(format!("{identifier} not found"))))?;
+            let get_message = |id: &str| {
+                self.bundle
+                    .get_message(id)
+                    .ok_or_else(|| PyValueError::new_err(format!("{id} not found")))
+            };
 
-            let pattern = msg.value().ok_or_else(|| {
-                PyValueError::new_err(format!("{identifier} - Message has no value.",))
-            })?;
+            let pattern = match identifier.split_once('.') {
+                Some((message_id, attribute_id)) => get_message(message_id)?
+                    .get_attribute(attribute_id)
+                    .ok_or_else(|| {
+                        PyValueError::new_err(format!(
+                            "{identifier} - Attribute '{attribute_id}' not found on message '{message_id}'."
+                        ))
+                    })?
+                    .value(),
+                    // Note: attribute.value() returns &Pattern directly (not Option)
+                    // because attributes always have values, unlike messages
+                None => get_message(identifier)?
+                    .value()
+                    .ok_or_else(|| {
+                        PyValueError::new_err(format!("{identifier} - Message has no value."))
+                    })?
+            };
 
             let mut args = FluentArgs::new();
 

tests/data/attributes.ftl

@@ -0,0 +1,20 @@
+# Test file for Fluent attributes
+welcome-message = Welcome!
+    .title = Welcome to our site
+    .aria-label = Welcome greeting
+
+login-input = Email
+    .placeholder = email@example.com
+    .aria-label = Login input value
+    .title = Type your login email
+
+# Message with variables in attributes
+greeting = Hello
+    .formal = Hello, { $name }
+    .informal = Hi { $name }!
+
+# Message with only attributes (no value)
+form-button =
+    .submit = Submit Form
+    .cancel = Cancel
+    .reset = Reset Form

tests/test_python_interface.py

@@ -207,3 +207,84 @@ def test_raises_parser_error_on_file_that_contains_errors_in_strict_mode():
 
 def test_parser_error_str():
     assert str(fluent.ParserError) == "<class 'rustfluent.ParserError'>"
+
+
+# Attribute access tests
+
+
+def test_basic_attribute_access():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    assert bundle.get_translation("welcome-message.title") == "Welcome to our site"
+
+
+def test_regular_message_still_works_with_attributes():
+    """Test that accessing the main message value still works when it has attributes."""
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    assert bundle.get_translation("welcome-message") == "Welcome!"
+
+
+def test_multiple_attributes_on_same_message():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    assert bundle.get_translation("login-input.placeholder") == "email@example.com"
+    assert bundle.get_translation("login-input.aria-label") == "Login input value"
+    assert bundle.get_translation("login-input.title") == "Type your login email"
+
+
+def test_attribute_with_variables():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    result = bundle.get_translation("greeting.formal", variables={"name": "Alice"})
+    assert result == f"Hello, {BIDI_OPEN}Alice{BIDI_CLOSE}"
+
+
+def test_attribute_with_variables_use_isolating_off():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    result = bundle.get_translation(
+        "greeting.informal",
+        variables={"name": "Bob"},
+        use_isolating=False,
+    )
+    assert result == "Hi Bob!"
+
+
+def test_attribute_on_message_without_main_value():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    assert bundle.get_translation("form-button.submit") == "Submit Form"
+    assert bundle.get_translation("form-button.cancel") == "Cancel"
+    assert bundle.get_translation("form-button.reset") == "Reset Form"
+
+
+def test_message_without_value_raises_error():
+    """Test that accessing a message without a value (only attributes) raises an error."""
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    with pytest.raises(ValueError, match="form-button - Message has no value"):
+        bundle.get_translation("form-button")
+
+
+def test_missing_message_with_attribute_syntax_raises_error():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    with pytest.raises(ValueError, match="nonexistent not found"):
+        bundle.get_translation("nonexistent.title")
+
+
+def test_missing_attribute_raises_error():
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    with pytest.raises(
+        ValueError,
+        match="welcome-message.nonexistent - Attribute 'nonexistent' not found on message 'welcome-message'",
+    ):
+        bundle.get_translation("welcome-message.nonexistent")
+
+
+@pytest.mark.parametrize(
+    "identifier,expected",
+    (
+        ("welcome-message", "Welcome!"),
+        ("welcome-message.title", "Welcome to our site"),
+        ("welcome-message.aria-label", "Welcome greeting"),
+        ("login-input", "Email"),
+        ("login-input.placeholder", "email@example.com"),
+    ),
+)
+def test_attribute_and_message_access_parameterized(identifier, expected):
+    bundle = fluent.Bundle("en", [data_dir / "attributes.ftl"])
+    assert bundle.get_translation(identifier) == expected