fix: prevent gap double subtraction causing unintended text wrapping

Author: TtTRz

.codebuddy/rules/anydev/rules/anydev.mdc

@@ -0,0 +1,16 @@
+---
+description: 
+globs:
+alwaysApply: true
+---
+
+<workflow>
+1. 始终以简洁的语言说明改动
+2. 代码要可读，函数/变量名要规范
+3. 所有的测试要有理论依据支持
+4. 所有注释都要英文
+5. 改动完之后，必须要跑测试
+6. 所有改动都要有理论依据，根据 W3C 或者 MDN 文档来
+7. 禁止脑补，要根据标准文档来
+8. 每次改完，都要跑一下 cargo clippy
+</workflow>

float-pigment-forest/tests/custom/css_flexbox/gap.rs

@@ -230,3 +230,59 @@ fn flex_item_with_gap_should_shrink_to_fit() {
     "#
     )
 }
+
+// Case: flex-grow sum below 1 with gap
+// Spec points:
+// - When the sum of flex-grow is less than 1, only part of free space is distributed
+// - Gap must be accounted exactly once in free-space computation
+#[test]
+fn gap_with_flex_grow_sum_below_one_should_not_double_subtract_gap() {
+    assert_xml!(
+        r#"
+        <div style="display: flex; width: 200px; gap: 20px;">
+          <div style="width: 50px; height: 20px; flex-grow: 0.2;" expect_width="66" expect_left="0"></div>
+          <div style="width: 50px; height: 20px; flex-grow: 0.2;" expect_width="66" expect_left="86"></div>
+        </div>
+    "#
+    )
+}
+
+// Case: flex-shrink sum below 1 with gap
+// Spec points:
+// - When the sum of flex-shrink is less than 1, shrink amount is scaled by the sum
+// - Gap must not be subtracted twice from remaining free space
+#[test]
+fn gap_with_flex_shrink_sum_below_one_should_not_double_subtract_gap() {
+    assert_xml!(
+        r#"
+        <div style="display: flex; width: 200px; gap: 20px;">
+          <div style="width: 150px; height: 20px; flex-shrink: 0.2;" expect_width="126" expect_left="0"></div>
+          <div style="width: 150px; height: 20px; flex-shrink: 0.2;" expect_width="126" expect_left="146"></div>
+        </div>
+    "#
+    )
+}
+
+// Case: nested flex with inner gap and outer space-between
+// Spec points:
+// - Inner flex gap should only affect spacing between its own items
+// - Outer space-between should place left and right groups without forcing unexpected text wrapping
+#[test]
+fn nested_flex_gap_with_space_between_should_keep_text_unwrapped() {
+    assert_xml!(
+        r#"
+        <div style="display: block; width: 300px; padding: 30px;">
+          <div style="display: flex; flex-direction: row; justify-content: space-between; align-items: center;">
+            <div style="display: flex; flex-direction: row; align-items: center; gap: 30px;" expect_width="124" expect_left="0">
+              <div style="height: 30px; width: 30px;" expect_width="30" expect_left="0"></div>
+              <text-slot len="4" expect_width="64" expect_left="60" expect_height="16"></text-slot>
+            </div>
+            <div style="display: flex; flex-direction: row;" expect_left="236">
+              <text-slot len="4" expect_width="64" expect_height="16"></text-slot>
+            </div>
+          </div>
+        </div>
+    "#,
+        true
+    )
+}

float-pigment-layout/src/algo/flex_box.rs

@@ -604,10 +604,12 @@ impl<T: LayoutTreeNode> FlexBox<T> for LayoutUnit<T> {
                             (flex_grow + child.flex_grow, flex_shrink + child.flex_shrink)
                         });
                 let free_space = if growing && sum_flex_grow < 1.0 {
-                    (initial_free_space.mul_f32(sum_flex_grow) - total_main_axis_gap)
+                    initial_free_space
+                        .mul_f32(sum_flex_grow)
                         .maybe_min(target_len - used_space)
                 } else if shrinking && sum_flex_shrink < 1.0 {
-                    (initial_free_space.mul_f32(sum_flex_shrink) - total_main_axis_gap)
+                    initial_free_space
+                        .mul_f32(sum_flex_shrink)
                         .maybe_max(target_len - used_space)
                 } else {
                     (target_len - used_space).or_zero()