Read a frozen changelog whose title is not the configured one

lib/src/Gren.js

@@ -35,6 +35,12 @@ const TAGS_LIMIT = 30;
 // The data sources whose releases are built from the commits each release contains.
 const MEMBERSHIP_DATA_SOURCES = ["prs", "prs-with-issues"];
 
+// Where a release section starts. The preamble a changelog opens with ends here, and a
+// changelog written without a separator is split here; the two have to agree on the answer.
+const RELEASE_HEADING = "#{1,6} +v?\\d+\\.\\d+\\.\\d+";
+const PREAMBLE_END = new RegExp(`^${RELEASE_HEADING}`, "m");
+const SECTION_SPLIT = new RegExp(`(?<=\\n)(?=${RELEASE_HEADING})`);
+
 /**
  * Get the semver version a tag or release name stands for
  *
@@ -350,12 +356,22 @@ class Gren {
       content = content.slice(changelogTitle.length);
     }
 
+    // The title in the file is not always the one in the configuration: a banner is added to
+    // it, or its wording changes. Whatever stands before the first release is title too, and
+    // leaving it in makes the preamble's first line the heading of the release under it, which
+    // drops that release from the file this run is about to write over it.
+    const firstRelease = content.search(PREAMBLE_END);
+
+    if (firstRelease > 0) {
+      content = content.slice(firstRelease);
+    }
+
     let current = null;
     // A changelog written with nothing between its releases can only be split on the headings,
     // at the start of each one so that the release before it keeps its last line.
     const chunks = releaseSeparator
       ? content.split(releaseSeparator)
-      : content.split(/(?<=\n)(?=#{1,6} +v?\d+\.\d+\.\d+)/);
+      : content.split(SECTION_SPLIT);
 
     chunks.forEach((chunk) => {
       const heading = chunk.trimStart().split("\n")[0];

test/Gren.membership.spec.js

@@ -707,6 +707,42 @@ describe("Gren release membership", () => {
       });
     });
 
+    it("Should read the first release under a title the configuration does not spell", () => {
+      // A banner, or any title edited since the file was written, is still title. Keying the
+      // first section off the configured changelogTitle alone leaves the leftover preamble
+      // attached to the release under it, and that release is then dropped from the file the
+      // next run writes.
+      fs.writeFileSync(
+        path.join(repo.dir, "CHANGELOG.md"),
+        "# Changelog\n\n> Sponsor this project.\n\n" + Object.values(sections).join(separator),
+      );
+
+      const gren = createGren({ frozenBefore: "2020-01-16", changelogFilename: "CHANGELOG.md" });
+      const read = gren._readChangelogSections();
+
+      assert.equal(read.get("2.0.0"), sections["2.0.0"]);
+      assert.equal(read.get("1.2.0"), sections["1.2.0"]);
+    });
+
+    it("Should read the first release under an unknown title without a separator", () => {
+      const plain = { "2.0.0": sections["2.0.0"], "1.2.0": sections["1.2.0"] };
+
+      fs.writeFileSync(
+        path.join(repo.dir, "CHANGELOG.md"),
+        "Release history\n===============\n\n" + Object.values(plain).join(""),
+      );
+
+      const gren = createGren({
+        frozenBefore: "2020-01-16",
+        changelogFilename: "CHANGELOG.md",
+        template: { releaseSeparator: "" },
+      });
+      const read = gren._readChangelogSections();
+
+      assert.equal(read.get("2.0.0"), plain["2.0.0"]);
+      assert.equal(read.get("1.2.0"), plain["1.2.0"]);
+    });
+
     it("Should read a changelog with nothing between its releases", async () => {
       const plain = { "2.0.0": sections["2.0.0"], "1.2.0": sections["1.2.0"] };