feat(conventional-commits): Preserve major version zero on breaking c…

…hanges (#2486)

According to semver, major version zero (0.y.z) is for initial
development. Anything MAY change at any time. The public API
SHOULD NOT be considered stable. The version 1.0.0 defines
the (initial stable) public API.

To allow monorepos to use major version zero meaningfully,
the transition from 0.x to 1.x must be explicitly requested
by the user. Breaking changes MUST NOT automatically bump
the major version from 0.x to 1.x.

The usual convention is to use semver-patch bumps for bugfix
releases and semver-minor for everything else, including
breaking changes. This matches the behavior of `^` operator
as implemented by `npm`.

This commit implements the convention described above:
- a patch-level change bumps semver-patch version (NO CHANGE)
- a minor-level change bumps semver-minor version (NO CHANGE)
- a major-level (breaking) change bumps semver-minor version (NEW)

Signed-off-by: Miroslav Bajtoš <mbajtoss@gmail.com>

core/conventional-commits/__tests__/__fixtures__/major-zero/lerna.json

@@ -0,0 +1,8 @@
+{
+  "command": {
+    "publish": {
+      "conventionalCommits": true
+    }
+  },
+  "version": "independent"
+}

core/conventional-commits/__tests__/__fixtures__/major-zero/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "conventional-commits-major-zero",
+  "repository": "lerna/conventional-commits-major-zero",
+  "version": "0.0.0-root"
+}

core/conventional-commits/__tests__/__fixtures__/major-zero/packages/package-0/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "package-0",
+  "repository": "lerna/conventional-commits-major-zero",
+  "version": "0.1.0"
+}

core/conventional-commits/__tests__/__fixtures__/major-zero/packages/package-1/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "package-1",
+  "repository": "lerna/conventional-commits-major-zero",
+  "version": "1.0.0"
+}

core/conventional-commits/__tests__/conventional-commits.test.js

@@ -217,6 +217,21 @@ describe("conventional-commits", () => {
       ).rejects.toThrow("Unable to load conventional-changelog preset 'conventional-changelog-garbage/pail'");
     });
 
+    describe("bump for major version zero", () => {
+      it("treats breaking changes as semver-minor", async () => {
+        const cwd = await initFixture("major-zero");
+        const [pkg0] = await getPackages(cwd);
+
+        // make a change in package-0
+        await pkg0.set("changed", 1).serialize();
+        await gitAdd(cwd, pkg0.manifestLocation);
+        await gitCommit(cwd, "feat: changed\n\nBREAKING CHANGE: changed");
+
+        const bump = await recommendVersion(pkg0, "independent", {});
+        expect(bump).toBe("0.2.0");
+      });
+    });
+
     describe("prerelease bumps", () => {
       let cwd;
       let pkg;

core/conventional-commits/lib/recommend-version.js

@@ -51,14 +51,34 @@ function recommendVersion(pkg, type, { changelogPreset, rootPath, tagPrefix, pre
 
         // result might be undefined because some presets are not consistent with angular
         // we still need to bump _something_ because lerna saw a change here
-        const releaseType = data.releaseType || "patch";
+        let releaseType = data.releaseType || "patch";
 
         if (prereleaseId) {
           const shouldBump = shouldBumpPrerelease(releaseType, pkg.version);
           const prereleaseType = shouldBump ? `pre${releaseType}` : "prerelease";
           log.verbose(type, "increment %s by %s", pkg.version, prereleaseType);
           resolve(semver.inc(pkg.version, prereleaseType, prereleaseId));
         } else {
+          if (semver.major(pkg.version) === 0) {
+            // According to semver, major version zero (0.y.z) is for initial
+            // development. Anything MAY change at any time. The public API
+            // SHOULD NOT be considered stable. The version 1.0.0 defines
+            // the (initial stable) public API.
+            //
+            // To allow monorepos to use major version zero meaningfully,
+            // the transition from 0.x to 1.x must be explicitly requested
+            // by the user. Breaking changes MUST NOT automatically bump
+            // the major version from 0.x to 1.x.
+            //
+            // The usual convention is to use semver-patch bumps for bugfix
+            // releases and semver-minor for everything else, including
+            // breaking changes. This matches the behavior of `^` operator
+            // as implemented by `npm`.
+            //
+            if (releaseType === "major") {
+              releaseType = "minor";
+            }
+          }
           log.verbose(type, "increment %s by %s", pkg.version, releaseType);
           resolve(semver.inc(pkg.version, releaseType));
         }