Fix tree reporter line highlighting

news/544.bugfix.rst

@@ -0,0 +1 @@
+Fix a bug where the tree reporter would fail to populate the code pane with relevant lines if the line where the allocation occurred was too near the start of the file.

src/memray/reporters/tree.py

@@ -95,16 +95,16 @@ async def update_text_area(self) -> None:
 
         text = self.query_one("#textarea", TextArea)
 
-        if self.frame.location is None:
+        if self.frame.location is None or self.frame.location == ROOT_NODE:
             text.clear()
             return
 
         _, file, line = self.frame.location
         delta = text.size.height // 2
-        lines = linecache.getlines(file)[line - delta : line + delta]
+        lines = linecache.getlines(file)[max(line - delta, 0) : line + delta]
 
         text.text = "\n".join(tuple(line.rstrip() for line in lines))
-        text.select_line((delta - 1))
+        text.select_line(line - 1 if delta >= line else delta - 1)
         text.show_line_numbers = False
 
     def _get_content_by_label_id(self) -> Dict[str, str]:
@@ -166,18 +166,21 @@ def watch_frame(self) -> None:
     def compose(self) -> ComposeResult:
         if self.frame is None:
             return
+
         delta = 3
 
-        if self.frame.location is not None:
-            _, file, line = self.frame.location
-            lines = linecache.getlines(file)[line - delta : line + delta]
-        else:
+        if self.frame.location is None or self.frame.location == ROOT_NODE:
             lines = []
+            selected_line = 0
+        else:
+            _, file, line = self.frame.location
+            lines = linecache.getlines(file)[max(line - delta, 0) : line + delta]
+            selected_line = line - 1 if delta >= line else delta - 1
 
         text = TextArea(
             "\n".join(lines), language="python", theme="dracula", id="textarea"
         )
-        text.select_line(delta + 1)
+        text.select_line(selected_line)
         text.show_line_numbers = False
         text.can_focus = False
         text.cursor_blink = False