🏗️🔧：fix four faults in landing a pull request

.github/PULL_REQUEST_TEMPLATE.md

@@ -40,7 +40,7 @@ https://open.inf.is/docs/handbook/style/commit-messages/ -- in short: a
 category emoji, then optionally an action, then `：` (U+FF1A), then what
 the change does, in 50 characters or fewer and with no `#NNNN` on the end.
 
-_Copy and paste one of the following emoji into description_ -- copy
+_Copy and paste one of the following emoji into the title_ -- copy
 rather than type, since some have a lookalike spelling that is not the
 one recognized here.
 

build/shared/commit-message.mts

@@ -120,7 +120,7 @@ const TRAILER_LINE = /^(?<token>[A-Za-z][\w-]*):[ \t]*(?<value>.*)$/;
 const ASSISTED_BY_VALUE = /^[^\s:]+:\S+( \S+)*$/;
 
 /** git folds a trailer whose value runs onto an indented line beneath it. */
-const CONTINUATION_LINE = /^\s/;
+export const CONTINUATION_LINE = /^\s/;
 
 /**
  * Each known token with the pattern that also matches it misspelt with a
@@ -423,7 +423,19 @@ export function validateCommitMessage(message: string) {
     problems.push('the line after the subject has to be blank');
   }
 
-  for (const line of rest) {
+  // Where the trailer block starts, or past the end when there is none. A
+  // trailer is one line by construction here: git would read a folded value,
+  // but `readTrailers` keeps only the token line, so wrapping a long
+  // `Signed-off-by:` to fit would put the author out of reach of the sign-off
+  // check. The block is exempt from the width limit rather than made to fit
+  // inside it, which is also what the limit is for -- prose that is read.
+  const paragraphs = paragraphsOf(rest);
+  const blockStart =
+    trailerBlockOf(paragraphs).length > 0
+      ? rest.length - (paragraphs.at(-1)?.length ?? 0)
+      : rest.length;
+
+  for (const [index, line] of rest.entries()) {
     // A line of dashes is why the trailers in this project have been going
     // unread: `---` is where git stops looking for them, and any longer run
     // splits the block in two so that only the half below it counts.
@@ -439,7 +451,11 @@ export function validateCommitMessage(message: string) {
     // No grapheme is fewer than one code unit, so a line of BODY_MAX code
     // units or fewer is within the limit whatever it is made of, and the
     // segmenter need not see it.
-    if (line.length > BODY_MAX && /\s/.test(line.trim())) {
+    if (
+      index < blockStart &&
+      line.length > BODY_MAX &&
+      /\s/.test(line.trim())
+    ) {
       const width = countGraphemes(line);
 
       if (width > BODY_MAX) {

build/shared/commit-message.test.mts

@@ -11,6 +11,7 @@ import { readFile } from 'node:fs/promises';
 import { describe, test } from 'node:test';
 import {
   ACTIONS,
+  BODY_MAX,
   CATEGORIES,
   readTrailers,
   validateCommitMessage,
@@ -366,6 +367,38 @@ describe('the vocabulary', () => {
   });
 });
 
+describe('the width limit', () => {
+  test('leaves a trailer that cannot be wrapped alone', () => {
+    // Folding this to fit would put the author on a continuation line, where
+    // `readTrailers` does not look and so `checkSignOff` could not match it.
+    const long =
+      'Signed-off-by: Christopher Alexander Montgomery ' +
+      '<christopher.montgomery@example.org>';
+    ok(long.length > BODY_MAX);
+    deepStrictEqual(
+      validateCommitMessage(`🏗️🔧：fix it\n\nA body line.\n\n${long}`),
+      []
+    );
+  });
+
+  test('still holds prose to it, in the same message', () => {
+    const problems = validateCommitMessage(
+      `🏗️🔧：fix it\n\n${'word '.repeat(20)}end\n\n` +
+        'Signed-off-by: Derek Lewis <derek@example.com>'
+    );
+    deepStrictEqual(problems.length, 1);
+    match(problems[0] ?? '', /the limit is 72/);
+  });
+
+  test('holds a long line in a paragraph that only looks like trailers', () => {
+    // Not a block, so git reads no trailers in it and it is prose after all.
+    const problems = validateCommitMessage(
+      `🏗️🔧：fix it\n\nSigned-off-by: Derek Lewis <derek@example.com>\n${'word '.repeat(20)}end`
+    );
+    ok(problems.some((problem) => /the limit is 72/.test(problem)));
+  });
+});
+
 describe('a message written to be slow', () => {
   // A commit message comes from whoever opened the pull request, and the
   // commit queue reads it holding credentials that can write here. How long

build/shared/landing.mts

@@ -11,7 +11,11 @@
  * the repositories in this organization do not agree on that yet.
  */
 
-import { linesOf, TRAILER_ORDER } from '@openinf/portal/build/commit-message';
+import {
+  CONTINUATION_LINE,
+  linesOf,
+  TRAILER_ORDER,
+} from '@openinf/portal/build/commit-message';
 
 /** One commit's message, split into the parts a landed message reuses. */
 export type CommitParts = {
@@ -34,9 +38,26 @@ export function partsOfMessage(message: string): CommitParts {
   const body: string[] = [];
   const trailers: string[] = [];
 
+  // A folded trailer travels with the line it belongs to. Read on its own an
+  // indented continuation carries no token, so it would be filed as body and
+  // stranded there -- and `Co-authored-by:` folded over two lines would land
+  // with the address left behind, which is attribution quietly lost.
+  let inTrailer = false;
+
   for (const line of rest) {
-    if (TRAILER_ORDER.includes(tokenOf(line))) trailers.push(line);
-    else body.push(line);
+    if (TRAILER_ORDER.includes(tokenOf(line))) {
+      trailers.push(line);
+      inTrailer = true;
+    } else if (
+      inTrailer &&
+      CONTINUATION_LINE.test(line) &&
+      line.trim() !== ''
+    ) {
+      trailers[trailers.length - 1] += `\n${line}`;
+    } else {
+      body.push(line);
+      inTrailer = false;
+    }
   }
 
   while (body.at(-1)?.trim() === '') body.pop();

build/shared/landing.test.mts

@@ -344,3 +344,48 @@ describe('checksVerdict and its own run', () => {
     );
   });
 });
+
+describe('a folded trailer', () => {
+  const folded = [
+    '🏗️🔧：fix it',
+    '',
+    'A body line.',
+    '',
+    'Co-authored-by: Jane Doe',
+    '    <jane@example.com>',
+    'Signed-off-by: Derek Lewis <derek@example.com>',
+  ].join('\n');
+
+  test('is one trailer, not a trailer and a stranded line', () => {
+    const parts = partsOfMessage(folded);
+    deepStrictEqual(parts.body, ['A body line.']);
+    deepStrictEqual(parts.trailers, [
+      'Co-authored-by: Jane Doe\n    <jane@example.com>',
+      'Signed-off-by: Derek Lewis <derek@example.com>',
+    ]);
+  });
+
+  test('lands with its value still attached to it', () => {
+    const message = composeLandingMessage(
+      [partsOfMessage(folded)],
+      'https://example.com/pull/1'
+    );
+    deepStrictEqual(message.split('\n'), [
+      'A body line.',
+      '',
+      'Co-authored-by: Jane Doe',
+      '    <jane@example.com>',
+      'Signed-off-by: Derek Lewis <derek@example.com>',
+      'PR-URL: https://example.com/pull/1',
+    ]);
+    deepStrictEqual(validateCommitMessage(`🏗️🔧：fix it\n\n${message}`), []);
+  });
+
+  test('does not swallow an indented body line after prose', () => {
+    const parts = partsOfMessage(
+      '🏗️🔧：fix it\n\nA body line.\n    an indented one\n\nPR-URL: x'
+    );
+    deepStrictEqual(parts.body, ['A body line.', '    an indented one']);
+    deepStrictEqual(parts.trailers, ['PR-URL: x']);
+  });
+});

build/tasks/land-pull-request.mts

@@ -232,15 +232,25 @@ try {
       // do with a stranger's commits is to not have them on disk at all.
       // GitHub returns them oldest first, which is the order to read them in,
       // and merges are dropped since their messages say nothing.
-      const messages: string[] = JSON.parse(
-        gh(
-          'api',
-          '--paginate',
-          `repos/${repository()}/pulls/${number}/commits`,
-          '--jq',
-          '[.[] | select(.parents | length < 2) | .commit.message]'
-        )
-      );
+      //
+      // `--jq` beside `--paginate` filters each page and prints the results
+      // one after another, so a branch past the first page of commits would
+      // hand `JSON.parse` several arrays in a row and land nothing. `--slurp`
+      // gathers the pages themselves into one array, and the filtering that
+      // `--jq` was doing happens here instead.
+      const pages: { parents: unknown[]; commit: { message: string } }[][] =
+        JSON.parse(
+          gh(
+            'api',
+            '--paginate',
+            '--slurp',
+            `repos/${repository()}/pulls/${number}/commits`
+          )
+        );
+      const messages = pages
+        .flat()
+        .filter((commit) => commit.parents.length < 2)
+        .map((commit) => commit.commit.message);
       const parts = messages.map((message) => partsOfMessage(message));
       const message = composeLandingMessage(
         parts,