Fix code block height with virtual list remeasure

Author: AprilNEA

crates/gpui-markdown/src/render.rs

@@ -8,7 +8,7 @@ use std::future::Future;
 use std::sync::Arc;
 
 use gpui::*;
-use gpui_component::{h_flex, scroll::ScrollableElement, v_flex, ActiveTheme};
+use gpui_component::{h_flex, v_flex, ActiveTheme};
 
 use crate::parser::{MarkdownElement, MarkdownParser};
 
@@ -235,6 +235,10 @@ impl RenderContext {
     fn code_block_cache_key(&self, index: usize) -> ElementId {
         ElementId::from((self.cache_key.clone(), format!("code-block-{}", index)))
     }
+
+    fn code_block_scroll_id(&self, index: usize) -> ElementId {
+        ElementId::from((self.cache_key.clone(), format!("code-block-scroll-{}", index)))
+    }
 }
 
 /// Render plain code without syntax highlighting, splitting by lines to avoid extra spacing
@@ -243,9 +247,15 @@ fn render_plain_code(code: &str) -> AnyElement {
     let code = code.trim_end_matches('\n');
     let lines: Vec<AnyElement> = code
         .lines()
-        .map(|line| div().child(line.to_string()).into_any_element())
+        .map(|line| {
+            div()
+                .whitespace_nowrap()
+                .flex_shrink_0()
+                .child(line.to_string())
+                .into_any_element()
+        })
         .collect();
-    v_flex().children(lines).into_any_element()
+    v_flex().flex_shrink_0().children(lines).into_any_element()
 }
 
 fn render_element(
@@ -330,7 +340,8 @@ fn render_element(
                 .p_3()
                 .text_sm()
                 .font_family("monospace")
-                .overflow_x_scrollbar()
+                .id(context.code_block_scroll_id(code_block_index))
+                .overflow_x_scroll()
                 .overflow_y_hidden();
 
             if let Some(lang) = lang_label {

docs/logs/2026-01-19.md

@@ -0,0 +1,28 @@
+# 2026-01-19 - Markdown Code Block Height + Virtual List Measurement
+
+## Summary
+- Fixed markdown code blocks rendering with a fixed/tall height by removing the scrollbar wrapper that forced size_full.
+- Added periodic re-measurement for visible assistant messages containing fenced code to pick up async markdown/highlight layout changes.
+
+## Context
+- After switching chat history to a virtual list with estimated sizes, code block heights stayed large even for 1-2 lines.
+- The UI showed tall, empty code blocks and inconsistent height updates during streaming/async parsing.
+
+## Root Cause
+- `overflow_x_scrollbar()` wraps the code block in a Scrollable that uses a `size_full()` container, which forces the code block to match the parent height.
+- Virtual list item sizing relied on cached estimates; async markdown/highlight updates could change real height without triggering re-measurement.
+
+## Changes
+- `crates/gpui-markdown/src/render.rs`
+  - Use `overflow_x_scroll()` instead of `overflow_x_scrollbar()` to avoid the size_full wrapper.
+- `src/message_list.rs`
+  - Track last measured time per item.
+  - Re-measure visible assistant messages that contain fenced code blocks on a short interval to catch async layout changes.
+
+## Result
+- Code block height now matches content length instead of a fixed tall box.
+- Virtual list item heights stay in sync when markdown/highlighting finishes.
+
+## Follow-ups
+- If a visible horizontal scrollbar is required, implement a custom scrollbar layer that does not enforce size_full.
+- Consider tuning the re-measure interval if needed for performance.