fix(config): handle unset and off values in editorconfig files

crates/biome_cli/tests/cases/editorconfig.rs

@@ -452,3 +452,48 @@ max_line_length = 300
         result,
     ));
 }
+
+#[test]
+fn should_emit_diagnostics() {
+    let mut fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+
+    let editorconfig = Path::new(".editorconfig");
+    fs.insert(
+        editorconfig.into(),
+        r#"
+[*]
+insert_final_newline = false
+"#,
+    );
+
+    let test_file = Path::new("test.js");
+    let contents = r#"console.log("foo");
+"#;
+    fs.insert(test_file.into(), contents);
+
+    let result = run_cli(
+        DynRef::Borrowed(&mut fs),
+        &mut console,
+        Args::from(
+            [
+                ("format"),
+                ("--write"),
+                ("--use-editorconfig=true"),
+                test_file.as_os_str().to_str().unwrap(),
+            ]
+            .as_slice(),
+        ),
+    );
+
+    assert!(result.is_ok(), "run_cli returned {result:?}");
+
+    assert_file_contents(&fs, test_file, contents);
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "should_emit_diagnostics",
+        fs,
+        console,
+        result,
+    ));
+}

crates/biome_cli/tests/snapshots/main_cases_editorconfig/should_emit_diagnostics.snap

@@ -0,0 +1,33 @@
+---
+source: crates/biome_cli/tests/snap_test.rs
+expression: content
+---
+## `.editorconfig`
+
+```editorconfig
+
+[*]
+insert_final_newline = false
+
+```
+
+## `test.js`
+
+```js
+console.log("foo");
+
+```
+
+# Emitted Messages
+
+```block
+configuration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  × Key 'insert_final_newline' is incompatible with biome: Biome always inserts a final newline. Set this option to true.
+
+
+```
+
+```block
+Formatted 1 file in <TIME>. No fixes applied.
+```

crates/biome_configuration/src/diagnostics.rs

@@ -246,7 +246,7 @@ pub enum EditorConfigDiagnostic {
     /// Failed to parse the .editorconfig file.
     ParseFailed(ParseFailedDiagnostic),
     /// An option is completely incompatible with biome.
-    Incompatible(InconpatibleDiagnostic),
+    Incompatible(IncompatibleDiagnostic),
     /// A glob pattern that biome doesn't support.
     UnknownGlobPattern(UnknownGlobPatternDiagnostic),
     /// A glob pattern that contains invalid syntax.
@@ -255,7 +255,7 @@ pub enum EditorConfigDiagnostic {
 
 impl EditorConfigDiagnostic {
     pub fn incompatible(key: impl Into<String>, message: impl Into<String>) -> Self {
-        Self::Incompatible(InconpatibleDiagnostic {
+        Self::Incompatible(IncompatibleDiagnostic {
             message: MessageAndDescription::from(
                 markup! { "Key '"{key.into()}"' is incompatible with biome: "{message.into()}}
                     .to_owned(),
@@ -299,7 +299,7 @@ pub struct ParseFailedDiagnostic {
     category = "configuration",
     severity = Error,
 )]
-pub struct InconpatibleDiagnostic {
+pub struct IncompatibleDiagnostic {
     #[message]
     #[description]
     pub message: MessageAndDescription,

crates/biome_configuration/src/editorconfig.rs

@@ -83,12 +83,14 @@ impl EditorConfig {
 #[derive(Debug, Clone, Deserialize, Default)]
 #[serde(default)]
 pub struct EditorConfigOptions {
-    indent_style: Option<IndentStyle>,
-    #[serde(deserialize_with = "deserialize_optional_indent_width_from_string")]
-    indent_size: Option<IndentWidth>,
-    end_of_line: Option<LineEnding>,
-    #[serde(deserialize_with = "deserialize_optional_line_width_from_string")]
-    max_line_length: Option<LineWidth>,
+    #[serde(deserialize_with = "deserialize_optional_value_from_string")]
+    indent_style: EditorconfigValue<IndentStyle>,
+    #[serde(deserialize_with = "deserialize_optional_value_from_string")]
+    indent_size: EditorconfigValue<IndentWidth>,
+    #[serde(deserialize_with = "deserialize_optional_value_from_string")]
+    end_of_line: EditorconfigValue<LineEnding>,
+    #[serde(deserialize_with = "deserialize_optional_value_from_string")]
+    max_line_length: EditorconfigValue<LineWidth>,
     // Not a biome option, but we need it to emit a diagnostic when this is set to false.
     #[serde(deserialize_with = "deserialize_optional_bool_from_string")]
     insert_final_newline: Option<bool>,
@@ -97,20 +99,20 @@ pub struct EditorConfigOptions {
 impl EditorConfigOptions {
     pub fn to_biome(self) -> PartialFormatterConfiguration {
         PartialFormatterConfiguration {
-            indent_style: self.indent_style,
-            indent_width: self.indent_size,
-            line_ending: self.end_of_line,
-            line_width: self.max_line_length,
+            indent_style: self.indent_style.into(),
+            indent_width: self.indent_size.into(),
+            line_ending: self.end_of_line.into(),
+            line_width: self.max_line_length.into(),
             ..Default::default()
         }
     }
 
     pub fn to_biome_override(self) -> OverrideFormatterConfiguration {
         OverrideFormatterConfiguration {
-            indent_style: self.indent_style,
-            indent_width: self.indent_size,
-            line_ending: self.end_of_line,
-            line_width: self.max_line_length,
+            indent_style: self.indent_style.into(),
+            indent_width: self.indent_size.into(),
+            line_ending: self.end_of_line.into(),
+            line_width: self.max_line_length.into(),
             ..Default::default()
         }
     }
@@ -121,13 +123,38 @@ impl EditorConfigOptions {
         if let Some(false) = self.insert_final_newline {
             errors.push(EditorConfigDiagnostic::incompatible(
                 "insert_final_newline",
-                "Biome always inserts a final newline.",
+                "Biome always inserts a final newline. Set this option to true.",
             ));
         }
         errors
     }
 }
 
+/// Represents a value in an .editorconfig file.
+#[derive(Debug, Clone, Deserialize, Default)]
+#[serde(untagged)]
+pub enum EditorconfigValue<T> {
+    /// The value was explicitly specified.
+    Explicit(T),
+    /// Use the default value for this option. This occurs when the value is `unset`.
+    Default,
+    /// The value was not specified.
+    #[default]
+    None,
+}
+
+// This is an `Into` because implementing `From` is not possible because you can't implement traits for a type you don't own.
+#[allow(clippy::from_over_into)]
+impl<T: Default> Into<Option<T>> for EditorconfigValue<T> {
+    fn into(self) -> Option<T> {
+        match self {
+            EditorconfigValue::Explicit(v) => Some(v),
+            EditorconfigValue::Default => Some(T::default()),
+            EditorconfigValue::None => None,
+        }
+    }
+}
+
 fn deserialize_bool_from_string<'de, D>(deserializer: D) -> Result<bool, D::Error>
 where
     D: Deserializer<'de>,
@@ -147,28 +174,21 @@ where
     deserialize_bool_from_string(deserializer).map(Some)
 }
 
-fn deserialize_optional_indent_width_from_string<'de, D>(
-    deserializer: D,
-) -> Result<Option<IndentWidth>, D::Error>
-where
-    D: Deserializer<'de>,
-{
-    let s = String::deserialize(deserializer)?;
-    IndentWidth::from_str(s.as_str())
-        .map_err(serde::de::Error::custom)
-        .map(Some)
-}
-
-fn deserialize_optional_line_width_from_string<'de, D>(
+fn deserialize_optional_value_from_string<'de, D, T>(
     deserializer: D,
-) -> Result<Option<LineWidth>, D::Error>
+) -> Result<EditorconfigValue<T>, D::Error>
 where
     D: Deserializer<'de>,
+    T: FromStr,
+    T::Err: std::fmt::Display,
 {
     let s = String::deserialize(deserializer)?;
-    LineWidth::from_str(s.as_str())
-        .map_err(serde::de::Error::custom)
-        .map(Some)
+    match s.as_str() {
+        "unset" | "off" => Ok(EditorconfigValue::Default),
+        _ => T::from_str(s.as_str())
+            .map_err(serde::de::Error::custom)
+            .map(EditorconfigValue::Explicit),
+    }
 }
 
 /// Turn an unknown glob pattern into a list of known glob patterns. This is part of a hack to support all editorconfig patterns.
@@ -410,6 +430,53 @@ insert_final_newline = false
         assert!(matches!(errors[0], EditorConfigDiagnostic::Incompatible(_)));
     }
 
+    #[test]
+    fn should_parse_editorconfig_with_unset_values() {
+        let input = r#"
+root = true
+
+[*]
+indent_style = unset
+indent_size = unset
+end_of_line = unset
+max_line_length = unset
+"#;
+
+        let conf = parse_str(input).expect("Failed to parse editorconfig");
+        assert!(matches!(
+            conf.options["*"].indent_style,
+            EditorconfigValue::Default
+        ));
+        assert!(matches!(
+            conf.options["*"].indent_size,
+            EditorconfigValue::Default
+        ));
+        assert!(matches!(
+            conf.options["*"].end_of_line,
+            EditorconfigValue::Default
+        ));
+        assert!(matches!(
+            conf.options["*"].max_line_length,
+            EditorconfigValue::Default
+        ));
+    }
+
+    #[test]
+    fn should_parse_editorconfig_with_max_line_length_off() {
+        let input = r#"
+root = true
+
+[*]
+max_line_length = off
+"#;
+
+        let conf = parse_str(input).expect("Failed to parse editorconfig");
+        assert!(matches!(
+            conf.options["*"].max_line_length,
+            EditorconfigValue::Default,
+        ));
+    }
+
     #[test]
     fn should_expand_glob_pattern_list() {
         let pattern = "package.json";