Move comment preview text into lib

The regex-heavy markdown stripping was untested in the component.

src/components/ReviewCommentList.svelte

@@ -5,6 +5,7 @@
   import type { Thread } from "@bindings/cob/thread/Thread";
 
   import type { Resolution } from "@app/lib/commentResolutions";
+  import { plainText } from "@app/lib/markdownPlain";
   import type { CommentAnchor } from "@app/lib/pierreComments";
   import { anchorOf, formatAnchorLines } from "@app/lib/pierreComments";
   import {
@@ -51,30 +52,9 @@
     return author.alias ?? truncateId(authorKey(author));
   }
 
-  /// Inline markdown, dropped down to the words it decorates. A row is a couple
-  /// of truncated lines, and on a narrow column the punctuation crowds out the
-  /// text that says what the comment is about. Deliberately shallow — this is a
-  /// preview, not a parser; the comment itself is one click away in the diff.
-  function plain(body: string): string {
-    return (
-      body
-        .replace(/!?\[([^\]]*)\]\([^)]*\)/gu, "$1")
-        .replace(/`/gu, "")
-        .replace(/~~(.+?)~~/gu, "$1")
-        // Emphasis only where a marker sits on a word boundary, so `snake_case`,
-        // `MAX_SIZE` and `_private` survive being read as italics.
-        .replace(/(^|[^\w])[*_]{1,2}([^*_]+?)[*_]{1,2}(?=[^\w]|$)/gu, "$1$2")
-        .replace(/^\s{0,3}#{1,6}\s+/gmu, "")
-        .replace(/^\s{0,3}>\s?/gmu, "")
-        .replace(/^\s{0,3}(?:[-+*]|\d+\.)\s+/gmu, "")
-        .replace(/\s+/gu, " ")
-        .trim()
-    );
-  }
-
   /// The last edit is the current text.
   function preview(comment: Comment<CodeLocation>): string {
-    return plain(comment.edits.at(-1)?.body ?? "");
+    return plainText(comment.edits.at(-1)?.body ?? "");
   }
 </script>
 

src/lib/markdownPlain.ts

@@ -0,0 +1,20 @@
+/// Inline markdown, dropped down to the words it decorates. A row is a couple
+/// of truncated lines, and on a narrow column the punctuation crowds out the
+/// text that says what the comment is about. Deliberately shallow — this is a
+/// preview, not a parser; the comment itself is one click away in the diff.
+export function plainText(body: string): string {
+  return (
+    body
+      .replace(/!?\[([^\]]*)\]\([^)]*\)/gu, "$1")
+      .replace(/`/gu, "")
+      .replace(/~~(.+?)~~/gu, "$1")
+      // Emphasis only where a marker sits on a word boundary, so `snake_case`,
+      // `MAX_SIZE` and `_private` survive being read as italics.
+      .replace(/(^|[^\w])[*_]{1,2}([^*_]+?)[*_]{1,2}(?=[^\w]|$)/gu, "$1$2")
+      .replace(/^\s{0,3}#{1,6}\s+/gmu, "")
+      .replace(/^\s{0,3}>\s?/gmu, "")
+      .replace(/^\s{0,3}(?:[-+*]|\d+\.)\s+/gmu, "")
+      .replace(/\s+/gu, " ")
+      .trim()
+  );
+}

tests/unit/markdownPlain.test.ts

@@ -0,0 +1,27 @@
+import { expect, test } from "vitest";
+
+import { plainText } from "@app/lib/markdownPlain";
+
+test.each([
+  ["[the docs](https://example.com)", "the docs"],
+  ["![diagram](a.png) here", "diagram here"],
+  ["run `npm test` now", "run npm test now"],
+  ["~~old~~ new", "old new"],
+  ["**bold** and _italic_", "bold and italic"],
+  ["__strong__ and *em*", "strong and em"],
+  ["# Heading", "Heading"],
+  ["### Deep heading", "Deep heading"],
+  ["> quoted\n> text", "quoted text"],
+  ["- one\n* two\n+ three\n1. four", "one two three four"],
+  ["line one\n\n  line two", "line one line two"],
+  ["  padded  ", "padded"],
+])("%j reads as %j", (markdown, expected) => {
+  expect(plainText(markdown)).toBe(expected);
+});
+
+test.each(["snake_case_name", "MAX_SIZE", "_private", "a*b*c"])(
+  "leaves %j alone",
+  text => {
+    expect(plainText(text)).toBe(text);
+  },
+);