fix: leave whitespace that ends a line out of the saved file

CHANGELOG.md

@@ -131,6 +131,7 @@ Leafdown uses lightweight [Keep a Changelog](https://keepachangelog.com/en/1.1.0
 - Show the backslashes that keep text literal when the Markdown source of bold, italic, or strikethrough is opened, as a link label already did, so text such as `**a \[b](c) d**` no longer reads as though it held a live link and an escaped `©` can be told apart from one the file preserves.
 - Keep character references written next to each other as they were written, so text such as `©©` no longer saves as the characters it names. Each one still opens as its own Markdown source, so breaking one leaves the others preserved.
 - Keep a link or image title in the quotation marks or parentheses it was written with, so a file holding `[Garden](garden.md 'Garden')` no longer comes back rewritten to double quotes. Editing an image no longer rewrites its title either.
+- Leave whitespace that ends a line out of the saved file, so a space typed at the end of a paragraph, heading, list item, quote, or table cell no longer writes a character that the next open discards and a second save then removes. Markdown drops such whitespace on read, so the space was already lost; the file now says so from the first save. Whitespace elsewhere on a line, a hard break, and whitespace inside fenced code are unchanged, and a space written as ` ` at one of those trimmed positions is now dropped on save for the same reason.
 
 ## [0.1.0-alpha.1] - 2026-07-10
 

src/features/editor/tests/markdownCompatibility.test.ts

@@ -1222,7 +1222,7 @@ describe("Typed link source", () => {
       setSelectionAtDocumentEnd(mounted.view);
       typeText(mounted.view, `${typed} `);
 
-      expect(mounted.getMarkdown()).toBe(`${typed} \n`);
+      expect(mounted.getMarkdown()).toBe(`${typed}\n`);
     },
   );
 
@@ -1236,13 +1236,115 @@ describe("Typed link source", () => {
     },
   );
 
-  it("writes an ordinary trailing space as itself", async () => {
+  it("leaves the space that follows typed source out of the line it ends", async () => {
     const mounted = await mountEditor("");
 
     setSelectionAtDocumentEnd(mounted.view);
     typeText(mounted.view, "plain tail ");
 
-    expect(mounted.getMarkdown()).toBe("plain tail \n");
+    expect(mounted.getMarkdown()).toBe("plain tail\n");
+  });
+});
+
+// A parse drops whitespace closing a line or a cell, so writing it produces a file that reloads as
+// a different document. The corpus guard cannot reach this: a file it has opened once no longer
+// holds such whitespace, so only an edit puts it there.
+describe("Line-final whitespace", () => {
+  const editThenReload = async (
+    initial: string,
+    edit: (mounted: MountedMilkdownEditor) => void,
+  ) => {
+    const edited = await mountEditor(initial);
+
+    edit(edited);
+
+    const firstSave = edited.getMarkdown();
+    const reloaded = await mountEditor(firstSave);
+
+    return {
+      firstSave,
+      reloadedText: reloaded.view.state.doc.textContent,
+      secondSave: reloaded.getMarkdown(),
+    };
+  };
+
+  const typeAtEnd = (typed: string) => (mounted: MountedMilkdownEditor) => {
+    setSelectionAtDocumentEnd(mounted.view);
+    typeText(mounted.view, typed);
+  };
+
+  it.each([
+    { expected: "plain\n", initial: "plain", name: "a paragraph", typed: " " },
+    {
+      expected: "plain tail\n",
+      initial: "plain tail",
+      name: "a paragraph holding a space",
+      typed: " ",
+    },
+    { expected: "*text*\n", initial: "*text*", name: "emphasis closing a paragraph", typed: " " },
+    { expected: "plain\n", initial: "plain", name: "a paragraph, typed twice", typed: "  " },
+    { expected: "plain\n", initial: "plain", name: "a paragraph, typed as a tab", typed: "\t" },
+    { expected: "# head\n", initial: "# head", name: "a heading", typed: " " },
+    { expected: "* item\n", initial: "- item", name: "a list item", typed: " " },
+    { expected: "> quote\n", initial: "> quote", name: "a blockquote", typed: " " },
+  ])(
+    "converges on $name after a space is typed at its end",
+    async ({ expected, initial, typed }) => {
+      const { firstSave, secondSave } = await editThenReload(initial, typeAtEnd(typed));
+
+      expect(firstSave).toBe(expected);
+      expect(secondSave).toBe(firstSave);
+    },
+  );
+
+  it("converges on a table cell after a space is typed at its end", async () => {
+    const { firstSave, secondSave } = await editThenReload(BASIC_TABLE_MARKDOWN, typeAtEnd(" "));
+
+    expect(secondSave).toBe(firstSave);
+  });
+
+  it("reloads the paragraph the editor showed before the space was typed", async () => {
+    const { reloadedText } = await editThenReload("plain", typeAtEnd(" "));
+
+    expect(reloadedText).toBe("plain");
+  });
+
+  it("converges where whitespace ends a line through a deletion rather than a keystroke", async () => {
+    const { firstSave, secondSave } = await editThenReload("plain x", (mounted) => {
+      const end = mounted.view.state.doc.content.size - 1;
+
+      mounted.view.dispatch(mounted.view.state.tr.delete(end - 1, end));
+    });
+
+    expect(firstSave).toBe("plain\n");
+    expect(secondSave).toBe(firstSave);
+  });
+
+  it("keeps a space that later text on the same line follows", async () => {
+    const { firstSave, secondSave } = await editThenReload("plain", (mounted) => {
+      setTextSelection(mounted.view, 6);
+      typeText(mounted.view, " tail");
+    });
+
+    expect(firstSave).toBe("plain tail\n");
+    expect(secondSave).toBe(firstSave);
+  });
+
+  it("keeps a space a hard break follows", async () => {
+    const { firstSave, secondSave } = await editThenReload("a\\\nb\n", (mounted) => {
+      setTextSelection(mounted.view, 2);
+      typeText(mounted.view, " ");
+    });
+
+    expect(firstSave).toBe("a \\\nb\n");
+    expect(secondSave).toBe(firstSave);
+  });
+
+  it("keeps whitespace inside fenced code, which no parse trims", async () => {
+    const { firstSave, secondSave } = await editThenReload("```\ncode\n```", typeAtEnd(" "));
+
+    expect(firstSave).toBe("```\ncode \n```\n");
+    expect(secondSave).toBe(firstSave);
   });
 });
 

src/features/editor/tests/sourceProjectionTypedLink.test.ts

@@ -234,7 +234,7 @@ describe("typed link source", () => {
 
     expect(getLinkTargets(mounted)).toEqual([]);
     expect(mounted.getMarkdown()).toBe(
-      moved ? "\\[test taillink](./test.html) \n" : "\\[test taillink](./test.html) tail\n",
+      moved ? "\\[test taillink](./test.html)\n" : "\\[test taillink](./test.html) tail\n",
     );
   });
 

src/features/editor/utils/markdownText.ts

@@ -1039,6 +1039,18 @@ export const serializeMarkdownRoot: NonNullable<RemarkStringifyHandlers["root"]>
   }
 };
 
+// A paragraph and a heading end their line where their last child ends, and a cell is read back
+// trimmed to its content, so whitespace closing any of them is whitespace the next parse drops.
+// Only the last child can hold it: `state.safe` encodes whitespace a line ending follows, and
+// Milkdown hoists whitespace out of a mark before the mark is written.
+const closesTrimmedContent = (
+  parent: { type: string; children: readonly unknown[] } | undefined,
+  index: number,
+) =>
+  parent !== undefined &&
+  WHOLE_LINE_PHRASING_PARENTS.has(parent.type) &&
+  index === parent.children.length - 1;
+
 const readPhrasingNeighbors = (
   parent: { type: string; children: readonly { type: string; value?: string }[] } | undefined,
   index: number,
@@ -1068,14 +1080,18 @@ export const serializeMarkdownText: NonNullable<RemarkStringifyHandlers["text"]>
   info,
 ) => {
   const { value } = node;
+  const childIndex = state.indexStack[state.indexStack.length - 1] ?? -1;
   const trailingWhitespace = TRAILING_WHITESPACE_PATTERN.exec(value)?.[0] ?? "";
-  const after = trailingWhitespace + info.after;
+  // Whitespace the parse drops is left out rather than encoded, so the file the editor writes is
+  // the file it reads back. Every other position keeps it raw, which is what `state.safe` would
+  // write there anyway and what a typed space beside literal source needs.
+  const writtenWhitespace = closesTrimmedContent(parent, childIndex) ? "" : trailingWhitespace;
+  const after = writtenWhitespace + info.after;
   const escaped = state.safe(value.slice(0, value.length - trailingWhitespace.length), {
     ...info,
     after,
   });
   const slots = decodeEscapes(escaped);
-  const childIndex = state.indexStack[state.indexStack.length - 1] ?? -1;
   const neighbors = readPhrasingNeighbors(parent, childIndex);
 
   relaxAttentionEscapes(
@@ -1100,5 +1116,5 @@ export const serializeMarkdownText: NonNullable<RemarkStringifyHandlers["text"]>
   relaxAutolinkLiteralEscapes(slots, info.before, after);
   relaxCharacterReferenceEscapes(slots, after);
 
-  return encodeEscapes(slots) + trailingWhitespace;
+  return encodeEscapes(slots) + writtenWhitespace;
 };