Fixed an issue with failing to parse changesets containing a complete…

…ly empty summary (#740)

* fix changeset parser fail when summary is empty

* following up on PR review

* Update packages/parse/src/index.test.ts

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* Update packages/parse/src/index.test.ts

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* add changeset

* Update packages/parse/src/index.test.ts

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* Update .changeset/light-cats-flow.md

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

.changeset/light-cats-flow.md

@@ -0,0 +1,6 @@
+---
+"@changesets/cli": patch
+"@changesets/parse": patch
+---
+
+Fixed an issue with failing to parse changesets containing a completely empty summary.

packages/parse/src/index.test.ts

@@ -136,6 +136,28 @@ describe("parsing a changeset", () => {
       summary: expectedSummary
     });
   });
+  it("should be fine if the summary body is completely empty and there is no trailing whitespace", () => {
+    const changesetMd = outdent`---
+    "cool-package": minor
+    ---`;
+
+    const changeset = parse(changesetMd);
+    expect(changeset).toEqual({
+      releases: [{ name: "cool-package", type: "minor" }],
+      summary: ""
+    });
+  });
+  it("should be fine if there is no summary body and the frontmatter has some trailing whitespace", () => {
+    const changesetMd = outdent`---
+    "cool-package": minor
+    --- `;
+
+    const changeset = parse(changesetMd);
+    expect(changeset).toEqual({
+      releases: [{ name: "cool-package", type: "minor" }],
+      summary: ""
+    });
+  });
   it("should be fine if the changeset is empty", () => {
     const changesetMd = outdent`---
     ---
@@ -148,6 +170,13 @@ describe("parsing a changeset", () => {
       summary: ""
     });
   });
+  it("should be fine if the changeset is empty and without any trailing whitespace", () => {
+    const changeset = parse(`---\n---`);
+    expect(changeset).toEqual({
+      releases: [],
+      summary: ""
+    });
+  });
   it("should be fine if the frontmatter is followed by a whitespace on the same line", () => {
     const changesetMd = outdent`---
     "cool-package": minor

packages/parse/src/index.ts

@@ -1,7 +1,7 @@
 import yaml from "js-yaml";
 import { Release, VersionType } from "@changesets/types";
 
-const mdRegex = /\s*---([^]*?)\n\s*---\s*\n([^]*)/;
+const mdRegex = /\s*---([^]*?)\n\s*---(\s*(?:\n|$)[^]*)/;
 
 export default function parseChangesetFile(
   contents: string