Support optional-catch-binding syntax in Babel pipeline

Author: novemberborn

lib/babel-pipeline.js

@@ -130,6 +130,7 @@ function build(projectDir, cacheDir, userOptions, compileEnhancements) {
 	const ensureStage4 = wantsStage4(userOptions, projectDir);
 	const containsAsyncGenerators = makeValueChecker('@babel/plugin-syntax-async-generators');
 	const containsObjectRestSpread = makeValueChecker('@babel/plugin-syntax-object-rest-spread');
+	const containsOptionalCatchBinding = makeValueChecker('@babel/plugin-syntax-optional-catch-binding');
 	const containsStage4 = makeValueChecker('../stage-4');
 	const containsTransformTestFiles = makeValueChecker('@ava/babel-preset-transform-test-files');
 
@@ -162,6 +163,9 @@ function build(projectDir, cacheDir, userOptions, compileEnhancements) {
 		if (!testOptions.plugins.some(containsObjectRestSpread)) { // TODO: Remove once Babel can parse this syntax unaided.
 			testOptions.plugins.unshift(createConfigItem('@babel/plugin-syntax-object-rest-spread', 'plugin'));
 		}
+		if (!testOptions.plugins.some(containsOptionalCatchBinding)) { // TODO: Remove once Babel can parse this syntax unaided.
+			testOptions.plugins.unshift(createConfigItem('@babel/plugin-syntax-optional-catch-binding', 'plugin'));
+		}
 		if (ensureStage4 && !testOptions.presets.some(containsStage4)) {
 			// Apply last.
 			testOptions.presets.unshift(createConfigItem('../stage-4', 'preset'));

package-lock.json

@@ -65,6 +65,7 @@
 		"@babel/generator": "7.0.0-beta.49",
 		"@babel/plugin-syntax-async-generators": "7.0.0-beta.49",
 		"@babel/plugin-syntax-object-rest-spread": "7.0.0-beta.49",
+		"@babel/plugin-syntax-optional-catch-binding": "7.0.0-beta.49",
 		"@concordance/react": "^1.0.0",
 		"ansi-escapes": "^3.1.0",
 		"ansi-styles": "^3.2.1",