Fix assignment width check for multiline variable lists

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed the parameters of an assigned function being expanded unnecessarily when the variable list, type specifier or attribute spans multiple lines
+
 ## [2.6.0] - 2026-10-10
 
 ### Added

src/formatters/assignment.rs

@@ -367,15 +367,15 @@ pub fn format_assignment_no_trivia(
         equal_token = prepend_newline_indent(ctx, &equal_token, shape);
     }
 
-    // Test the assignment to see if its over width
-    let singleline_shape = shape
-        + (strip_leading_trivia(&var_list).to_string().len()
-            + 3
-            + strip_trailing_trivia(&expr_list).to_string().len());
+    // Test the assignment to see if its over width. The variable list may span multiple lines
+    // (e.g. a multiline table constructor), so only its last line is followed by the equals token.
+    let singleline_shape = shape.take_last_line(&strip_leading_trivia(&var_list))
+        + 3 // 3 = " = "
+        + strip_trailing_trivia(&expr_list).to_string().len();
     if contains_comments || singleline_shape.over_budget() {
         // We won't attempt anything else with the var_list. Format it normally
         var_list = try_format_punctuated(ctx, assignment.variables(), shape, format_var, Some(1));
-        let shape = shape + (strip_leading_trivia(&var_list).to_string().len() + 3);
+        let shape = shape.take_last_line(&strip_leading_trivia(&var_list)) + 3; // 3 = " = "
 
         let (new_expr_list, new_equal_token) =
             attempt_assignment_tactics(ctx, assignment.expressions(), shape, equal_token);
@@ -489,20 +489,25 @@ pub fn format_local_assignment_no_trivia(
             .map(|x| x.map(|type_specifier| format_type_specifier(ctx, type_specifier, shape)))
             .collect();
 
+        // Attributes and type specifiers follow the name list, before the equals token. Only their
+        // last line shares a line with the equals token, so collect their text and measure the
+        // last line of the whole variable list rather than summing up lengths.
         #[allow(unused_mut)]
-        let mut type_specifier_len = 0;
+        let mut var_list_suffix = String::new();
         #[cfg(feature = "lua54")]
-        {
-            type_specifier_len += attributes.iter().fold(0, |acc, x| {
-                acc + x.as_ref().map_or(0, |y| y.to_string().len())
-            });
-        }
+        var_list_suffix.extend(
+            attributes
+                .iter()
+                .flatten()
+                .map(|attribute| attribute.to_string()),
+        );
         #[cfg(feature = "luau")]
-        {
-            type_specifier_len += type_specifiers.iter().fold(0, |acc, x| {
-                acc + x.as_ref().map_or(0, |y| y.to_string().len())
-            });
-        }
+        var_list_suffix.extend(
+            type_specifiers
+                .iter()
+                .flatten()
+                .map(|specifier| specifier.to_string()),
+        );
 
         #[cfg(feature = "luau")]
         let var_list_ends_with_comments = match type_specifiers.last() {
@@ -525,13 +530,14 @@ pub fn format_local_assignment_no_trivia(
             equal_token = prepend_newline_indent(ctx, &equal_token, shape);
         }
 
-        // Test the assignment to see if its over width
-        let singleline_shape = shape
-            + (strip_leading_trivia(&name_list).to_string().len()
-                + 6 // 6 = "local "
-                + 3 // 3 = " = "
-                + type_specifier_len
-                + strip_trailing_trivia(&expr_list).to_string().len());
+        // Test the assignment to see if its over width. The name list, attributes and type
+        // specifiers may all span multiple lines, so only their last line is followed by the
+        // equals token.
+        let var_list = format!("{}{}", strip_leading_trivia(&name_list), var_list_suffix);
+        let singleline_shape = (shape + 6) // 6 = "local "
+            .take_last_line(&var_list)
+            + 3 // 3 = " = "
+            + strip_trailing_trivia(&expr_list).to_string().len();
 
         if contains_comments || singleline_shape.over_budget() {
             // We won't attempt anything else with the name_list. Format it normally
@@ -542,8 +548,9 @@ pub fn format_local_assignment_no_trivia(
                 format_token_reference,
                 Some(1),
             );
-            let shape = shape
-                + (strip_leading_trivia(&name_list).to_string().len() + 6 + 3 + type_specifier_len);
+            let shape = (shape + 6) // 6 = "local "
+                .take_last_line(&var_list)
+                + 3; // 3 = " = "
 
             let (new_expr_list, new_equal_token) =
                 attempt_assignment_tactics(ctx, assignment.expressions(), shape, equal_token);
@@ -621,9 +628,17 @@ pub fn format_const_assignment_no_trivia(
         .map(|x| x.map(|type_specifier| format_type_specifier(ctx, type_specifier, shape)))
         .collect();
 
-    let type_specifier_len = type_specifiers.iter().fold(0, |acc, x| {
-        acc + x.as_ref().map_or(0, |y| y.to_string().len())
-    });
+    // Type specifiers follow the name list, before the equals token. Only their last line shares a
+    // line with the equals token, so append their text to the name list and measure the last line.
+    let var_list = format!(
+        "{}{}",
+        strip_leading_trivia(&name_list),
+        type_specifiers
+            .iter()
+            .flatten()
+            .map(|specifier| specifier.to_string())
+            .collect::<String>()
+    );
 
     let var_list_ends_with_comments = match type_specifiers.last() {
         Some(Some(specifier)) => {
@@ -641,12 +656,12 @@ pub fn format_const_assignment_no_trivia(
         equal_token = prepend_newline_indent(ctx, &equal_token, shape);
     }
 
-    let singleline_shape = shape
-        + (strip_leading_trivia(&name_list).to_string().len()
-            + 6 // 6 = "const "
-            + 3 // 3 = " = "
-            + type_specifier_len
-            + strip_trailing_trivia(&expr_list).to_string().len());
+    // The name list and type specifiers may span multiple lines (e.g. due to comments), so only
+    // their last line is followed by the equals token.
+    let singleline_shape = (shape + 6) // 6 = "const "
+        .take_last_line(&var_list)
+        + 3 // 3 = " = "
+        + strip_trailing_trivia(&expr_list).to_string().len();
 
     if contains_comments || singleline_shape.over_budget() {
         name_list = try_format_punctuated(
@@ -656,8 +671,9 @@ pub fn format_const_assignment_no_trivia(
             format_token_reference,
             Some(1),
         );
-        let shape = shape
-            + (strip_leading_trivia(&name_list).to_string().len() + 6 + 3 + type_specifier_len);
+        let shape = (shape + 6) // 6 = "const "
+            .take_last_line(&var_list)
+            + 3; // 3 = " = "
 
         let (new_expr_list, new_equal_token) =
             attempt_assignment_tactics(ctx, assignment.expressions(), shape, equal_token);

tests/tests.rs

@@ -263,6 +263,207 @@ end)
     );
 }
 
+#[test]
+fn test_assignment_var_list_spanning_multiple_lines() {
+    // The variable list spans multiple lines (a multiline table constructor passed to a function
+    // call), so only its last line (`}).g`) shares a line with the equals token. The width check
+    // must measure that line, not the total length of the variable list: otherwise the function
+    // parameters are incorrectly expanded onto multiple lines once the table grows.
+    insta::assert_snapshot!(
+        format_code(
+            r#"f("s", {
+	{ a = 1 },
+	{ b = 2 },
+	{ c = 3 },
+}).g = function(h)
+	return h
+end
+"#,
+            Config {
+                column_width: 40,
+                ..Config::default()
+            },
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    f("s", {
+    	{ a = 1 },
+    	{ b = 2 },
+    	{ c = 3 },
+    }).g = function(h)
+    	return h
+    end
+    "###
+    );
+}
+
+#[test]
+fn test_assignment_var_list_spanning_multiple_lines_still_expands_when_over_budget() {
+    // Same shape as above, but the parameters genuinely do not fit after the last line of the
+    // variable list, so they must still be expanded. This guards the fix from being too permissive.
+    insta::assert_snapshot!(
+        format_code(
+            r#"f("s", {
+	{ a = 1 },
+}).g = function(first_argument, second_argument)
+	return first_argument
+end
+"#,
+            Config {
+                column_width: 40,
+                ..Config::default()
+            },
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    f("s", {
+    	{ a = 1 },
+    }).g = function(
+    	first_argument,
+    	second_argument
+    )
+    	return first_argument
+    end
+    "###
+    );
+}
+
+#[test]
+fn test_local_assignment_name_list_spanning_multiple_lines() {
+    // The name list spans multiple lines because of the comment, so only its last line
+    // (`variable_06, variable_07`) shares a line with the equals token. Measuring the total
+    // length of the name list instead would expand the function parameters unnecessarily.
+    insta::assert_snapshot!(
+        format_code(
+            r#"local variable_01, variable_02, variable_03, variable_04, variable_05, -- note
+	variable_06, variable_07 = function(h)
+	return h
+end
+"#,
+            Config::default(),
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    local variable_01,
+    	variable_02,
+    	variable_03,
+    	variable_04,
+    	variable_05, -- note
+    	variable_06,
+    	variable_07 = function(h)
+    	return h
+    end
+    "###
+    );
+}
+
+#[test]
+#[cfg(feature = "luau")]
+fn test_const_assignment_name_list_spanning_multiple_lines() {
+    // Same as above, for Luau `const` declarations.
+    insta::assert_snapshot!(
+        format_code(
+            r#"const a, -- note
+	b = function(h)
+	return h
+end, 2
+"#,
+            Config {
+                syntax: LuaVersion::Luau,
+                column_width: 40,
+                ..Config::default()
+            },
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    const a, -- note
+    	b = function(h)
+    	return h
+    end, 2
+    "###
+    );
+}
+
+#[test]
+#[cfg(feature = "luau")]
+fn test_local_assignment_multiline_type_specifier() {
+    // The type specifier spans multiple lines, so only its last line (`}`) shares a line with the
+    // equals token. Its total length must not be counted, or the function parameters get expanded
+    // unnecessarily.
+    insta::assert_snapshot!(
+        format_code(
+            r#"local x: {
+	a: string,
+	b: string,
+	c: string,
+} = function(h)
+	return h
+end
+"#,
+            Config {
+                syntax: LuaVersion::Luau,
+                column_width: 40,
+                ..Config::default()
+            },
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    local x: {
+    	a: string,
+    	b: string,
+    	c: string,
+    } = function(h)
+    	return h
+    end
+    "###
+    );
+}
+
+#[test]
+#[cfg(feature = "luau")]
+fn test_const_assignment_multiline_type_specifier() {
+    // Same as above, for Luau `const` declarations.
+    insta::assert_snapshot!(
+        format_code(
+            r#"const x: {
+	a: string,
+	b: string,
+	c: string,
+} = function(h)
+	return h
+end
+"#,
+            Config {
+                syntax: LuaVersion::Luau,
+                column_width: 40,
+                ..Config::default()
+            },
+            None,
+            OutputVerification::None
+        )
+        .unwrap(),
+        @r###"
+    const x: {
+    	a: string,
+    	b: string,
+    	c: string,
+    } = function(h)
+    	return h
+    end
+    "###
+    );
+}
+
 #[test]
 fn test_preserve_block_newline_gaps() {
     insta::glob!("inputs-preserve-block-newline-gaps/*.lua", |path| {