feat: Expect plugins to return Promises

BREAKING CHANGE: Each plugin is expected to return an async function or a Promise returning function. The callback parameter is not passed to plugins anymore.

test/fixtures/multi-plugin.js

@@ -1,21 +1,8 @@
 module.exports = {
-  verifyConditions(config, options, cb) {
-    cb();
-  },
-
-  getLastRelease(config, options, cb) {
-    cb();
-  },
-  analyzeCommits(config, options, cb) {
-    cb();
-  },
-  verifyRelease(config, options, cb) {
-    cb();
-  },
-  generateNotes(config, options, cb) {
-    cb();
-  },
-  publish(config, options, cb) {
-    cb();
-  },
+  verifyConditions: () => {},
+  getLastRelease: () => {},
+  analyzeCommits: () => {},
+  verifyRelease: () => {},
+  generateNotes: () => {},
+  publish: () => {},
 };

test/fixtures/plugin-error-inherited.js

@@ -9,6 +9,6 @@ class InheritedError extends SemanticReleaseError {
   }
 }
 
-module.exports = function(config, options, cb) {
-  cb(new InheritedError('Inherited error', 'EINHERITED'));
+module.exports = () => {
+  throw new InheritedError('Inherited error', 'EINHERITED');
 };

test/fixtures/plugin-error.js

@@ -1,5 +1,5 @@
-module.exports = function(config, options, cb) {
+module.exports = () => {
   const error = new Error('a');
   error.errorProperty = 'errorProperty';
-  cb(error);
+  throw error;
 };

test/fixtures/plugin-noop.js

@@ -1,3 +1 @@
-module.exports = (config, options, cb) => {
-  cb(null);
-};
+module.exports = () => {};

test/fixtures/plugin-result-config.js

@@ -1,3 +1 @@
-module.exports = function(pluginConfig, options, cb) {
-  cb(null, {pluginConfig, options});
-};
+module.exports = (pluginConfig, options) => ({pluginConfig, options});