feat: add execasync CLI flag to make execa calls be always synchronous

closes #1

README.md

@@ -120,7 +120,7 @@ The integration with semantic release is pretty janky — this is a quick summar
   - Had to duplicate the internal cosmiconfig setup from semantic release to get this working :(
 4. I found Git getting itself into weird states because e.g. `git tag` is done asynchronously
   - To get around this I had to stagger package publishing so they were done one at a time (which slows things down)
-  - I think calls to `execa()` in semantic release should be replaced with `execa.sync()` to ensure Git's internal state is atomic.
+  - I think calls to `execa()` in semantic release should be replaced with `execa.sync()` to ensure Git's internal state is atomic. For an experiment, you may add `--execasync` CLI flag that makes all calls synchronous through [ritm-hook](https://github.com/elastic/require-in-the-middle).
 
 ### Git tags
 

bin/cli.js

@@ -1,5 +1,10 @@
 #!/usr/bin/env node
 
+// Execa hook.
+if (require("yargs").argv.execasync) {
+	require("../lib/execaHook").hook()
+}
+
 // Imports.
 const getWorkspacesYarn = require("../lib/getWorkspacesYarn");
 const multiSemanticRelease = require("../lib/multiSemanticRelease");

lib/execaHook.js

@@ -0,0 +1,54 @@
+// NOTE this workaround forces execa calls to be always sync
+// Discussion: https://github.com/semantic-release/semantic-release/issues/193#issuecomment-462063871
+
+const execa = require('execa')
+const ritm = require('require-in-the-middle')
+
+let interceptor
+
+const uncache = () => delete require.cache[require.resolve('execa')]
+
+const getExecaSyncPromisified = () => Object.assign((...args) => {
+  const result = new Promise((resolve, reject) => {
+    try {
+      resolve(execa.sync(...args))
+    } catch (e) {
+      reject(e)
+    }
+  })
+
+  result.stdout = new String('')
+  result.stderr = new String('')
+  result.stdout.pipe = () => {}
+  result.stderr.pipe = () => {}
+
+  return result
+}, execa)
+
+const hook = () => {
+  if (interceptor) {
+    return
+  }
+
+  const execaHooked = getExecaSyncPromisified()
+
+  interceptor = ritm(['execa'], () => execaHooked)
+  uncache()
+
+  console.log('"execa" hooked')
+}
+
+const unhook = () => {
+  if (interceptor) {
+    interceptor.unhook()
+    interceptor = null
+    uncache()
+
+    console.log('"execa" unhooked')
+  }
+}
+
+module.exports = {
+  hook,
+  unhook
+}

package.json

@@ -47,7 +47,8 @@
 		"semver": "^5.6.0",
 		"signale": "^1.2.0",
 		"stream-buffers": "^3.0.2",
-		"tempy": "^0.2.1"
+		"tempy": "^0.2.1",
+		"yargs": "^13.2.2"
 	},
 	"devDependencies": {
 		"@commitlint/config-conventional": "^7.3.1",