feat: Port in use checking for development server

packages/cli/package.json

@@ -55,6 +55,7 @@
     "param-case": "3.0.4",
     "pascalcase": "1.0.0",
     "pluralize": "8.0.0",
+    "portfinder": "^1.0.32",
     "prettier": "2.7.1",
     "prisma": "4.3.1",
     "prompts": "2.4.2",

packages/cli/src/commands/devHandler.js

@@ -2,6 +2,8 @@ import fs from 'fs'
 import { argv } from 'process'
 
 import concurrently from 'concurrently'
+import portfinder from 'portfinder'
+import prompts from 'prompts'
 
 import { getConfig } from '@redwoodjs/internal/dist/config'
 import { shutdownPort } from '@redwoodjs/internal/dist/dev'
@@ -49,8 +51,78 @@ export const handler = async ({
   }
 
   if (side.includes('web')) {
+    let proposedPort = parseInt(getConfig().web.port)
+    const forwardedPortMatches = forward.match(
+      /--port=[0-9][0-9]?[0-9]?[0-9]?[0-9]? ?/
+    )
+    const forwardedPortSet =
+      forwardedPortMatches !== null && forwardedPortMatches.length == 1
+    if (forwardedPortSet) {
+      proposedPort = parseInt(
+        forwardedPortMatches[0]
+          .substring(forwardedPortMatches[0].indexOf('=') + 1)
+          .trim()
+      )
+    }
+
+    const availablePort = await portfinder.getPortPromise({
+      port: proposedPort,
+      stopPort: proposedPort + 64,
+    })
+    if (availablePort != proposedPort) {
+      if (availablePort == -1) {
+        console.error(
+          c.error(
+            `${
+              forwardedPortSet ? 'Forwarded' : 'Configured'
+            } "web" port ${proposedPort} is already in use and no neighbouring port is available! Cannot start development server.`
+          )
+        )
+        console.log(
+          c.info(
+            `Configured port can be updated in 'redwood.toml' or can be forwarded via the command line parameter like so 'yarn rw dev --fwd="--port=12345"'.`
+          )
+        )
+        process.exit(1)
+      } else {
+        console.error(
+          c.error(
+            `${
+              forwardedPortSet ? 'Forwarded' : 'Configured'
+            } "web" port ${proposedPort} is already in use!`
+          )
+        )
+        const useAvailablePort = await prompts({
+          type: 'confirm',
+          name: 'port',
+          message: `Do you wish to use port ${availablePort} instead?`,
+          initial: true,
+          active: 'Yes',
+          inactive: 'No',
+        })
+        if (useAvailablePort.port) {
+          // TODO: Consider if there is a better way to propagate the port?
+          if (forwardedPortSet) {
+            forward = forward.replace(
+              forwardedPortMatches[0],
+              ` --port=${availablePort}`
+            )
+          } else {
+            forward = forward.concat(` --port=${availablePort}`)
+          }
+        } else {
+          console.log(
+            c.info(
+              `Configured port can be updated in 'redwood.toml' or can be forwarded via the command line parameter like so 'yarn rw dev --fwd="--port=12345"'.`
+            )
+          )
+          process.exit(1)
+        }
+      }
+    }
+
     try {
-      await shutdownPort(getConfig().web.port)
+      await shutdownPort(availablePort)
     } catch (e) {
       errorTelemetry(process.argv, `Error shutting down "web": ${e.message}`)
       console.error(

packages/internal/package.json

@@ -68,6 +68,7 @@
     "@types/babel__core": "7.1.19",
     "@types/findup-sync": "4.0.2",
     "@types/fs-extra": "9.0.13",
+    "@types/node": "16.11.47",
     "@types/rimraf": "3.0.2",
     "babel-plugin-tester": "10.1.0",
     "graphql-tag": "2.12.6",