fix(formatter): measuring multiline text in fits_text is incorrect

crates/oxc_formatter/src/formatter/format_element/mod.rs

@@ -412,8 +412,10 @@ impl Width {
 /// that it is a multiline text if it contains a line feed.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum TextWidth {
+    /// Single-line text width
     Width(Width),
-    Multiline,
+    /// Multi-line text whose `width` is from the start of the text to the first line break
+    Multiline(Width),
 }
 
 impl TextWidth {
@@ -424,7 +426,7 @@ impl TextWidth {
         for c in text.chars() {
             let char_width = match c {
                 '\t' => indent_width.value(),
-                '\n' => return TextWidth::Multiline,
+                '\n' => return Self::Multiline(Width::new(width)),
                 #[expect(clippy::cast_possible_truncation)]
                 c => c.width().unwrap_or(0) as u8,
             };
@@ -444,14 +446,7 @@ impl TextWidth {
         TextWidth::Width(Width::new(len as u32))
     }
 
-    pub const fn width(self) -> Option<Width> {
-        match self {
-            TextWidth::Width(width) => Some(width),
-            TextWidth::Multiline => None,
-        }
-    }
-
     pub(crate) const fn is_multiline(self) -> bool {
-        matches!(self, TextWidth::Multiline)
+        matches!(self, TextWidth::Multiline(_))
     }
 }

crates/oxc_formatter/src/formatter/printer/mod.rs

@@ -626,16 +626,22 @@ impl<'a> Printer<'a> {
                 }
                 self.state.line_width += text.len();
             }
-            Text::Text { text, width } => {
-                if let Some(width) = width.width() {
+            Text::Text { text, width } => match width {
+                TextWidth::Width(width) => {
                     self.state.buffer.print_str(text);
                     self.state.line_width += width.value() as usize;
-                } else {
-                    for char in text.chars() {
+                }
+                TextWidth::Multiline(width) => {
+                    let line_break_position = text.find('\n').unwrap_or(text.len());
+                    let (first_line, remaining) = text.split_at(line_break_position);
+                    self.state.buffer.print_str(first_line);
+                    self.state.line_width += width.value() as usize;
+                    // Print the remaining lines
+                    for char in remaining.chars() {
                         self.print_char(char);
                     }
                 }
-            }
+            },
         }
 
         self.state.has_empty_line = false;
@@ -1171,19 +1177,21 @@ impl<'a, 'print> FitsMeasurer<'a, 'print> {
             Text::Token(text) => {
                 self.state.line_width += text.len();
             }
-            Text::Text { text, width } => {
-                if let Some(width) = width.width() {
+            Text::Text { text, width } => match width {
+                TextWidth::Width(width) => {
                     self.state.line_width += width.value() as usize;
-                } else {
+                }
+                TextWidth::Multiline(width) => {
                     return if self.must_be_flat
-                        || self.state.line_width > usize::from(self.options().print_width)
+                        || self.state.line_width + width.value() as usize
+                            > usize::from(self.options().print_width)
                     {
                         Fits::No
                     } else {
                         Fits::Yes
                     };
                 }
-            }
+            },
         }
 
         if self.state.line_width > usize::from(self.options().print_width) {

crates/oxc_formatter/tests/fixtures/js/calls/test.js

@@ -22,4 +22,8 @@ test.only("Test only", () => {});
 describe.only("Describe only", () => {});
 it.only("It only", () => {});
 
-test(code.replace((c) => ""), () => {});
+test(code.replace((c) => ""), () => {});
+
+expect(content)
+  .toMatch(`props: /*@__PURE__*/_mergeDefaults(['foo', 'bar', 'baz'], {
+})`)

crates/oxc_formatter/tests/fixtures/js/calls/test.js.snap

@@ -27,6 +27,11 @@ describe.only("Describe only", () => {});
 it.only("It only", () => {});
 
 test(code.replace((c) => ""), () => {});
+
+expect(content)
+  .toMatch(`props: /*@__PURE__*/_mergeDefaults(['foo', 'bar', 'baz'], {
+})`)
+
 ==================== Output ====================
 // Test patterns with multiple levels should not break incorrectly
 test.describe.serial("My test suite", () => {
@@ -57,4 +62,8 @@ test(
   () => {},
 );
 
+expect(content)
+  .toMatch(`props: /*@__PURE__*/_mergeDefaults(['foo', 'bar', 'baz'], {
+})`);
+
 ===================== End =====================