feat: warn about root paths without a leading slash (#2591)

* fix(create-matcher): warn about root paths without a leading slash

close #2550

* fix(create-route-map): warn about root paths without a leading slash

close #2550

* fix(create-route-map): only warn about first route without slash

* fix(create-route-map): handle case of '' route

* fix(create-route-map): remove leftover console.log

* fix(create-route-map): warn about root paths only

* fix(create-route-map): show prettier warning message

src/create-route-map.js

@@ -34,6 +34,18 @@ export function createRouteMap (
     }
   }
 
+  if (process.env.NODE_ENV === 'development') {
+    // warn if routes do not include leading slashes
+    const found = pathList
+    // check for missing leading slash
+      .filter(path => path && path.charAt(0) !== '*' && path.charAt(0) !== '/')
+
+    if (found.length > 0) {
+      const pathNames = found.map(path => `- ${path}`).join('\n')
+      warn(false, `Non-nested routes must include a leading slash character. Fix the following routes: \n${pathNames}`)
+    }
+  }
+
   return {
     pathList,
     pathMap,

test/unit/specs/create-map.spec.js

@@ -138,6 +138,31 @@ describe('Creating Route Map', function () {
     )
   })
 
+  it('in development, warn if a path is missing a leading slash', function () {
+    process.env.NODE_ENV = 'development'
+    maps = createRouteMap([
+      { path: 'bar', name: 'bar', component: Bar }
+    ])
+    expect(console.warn).toHaveBeenCalledTimes(1)
+    expect(console.warn.calls.argsFor(0)[0]).toEqual('[vue-router] Non-nested routes must include a leading slash character. Fix the following routes: \n- bar')
+  })
+
+  it('in development, it does not log the missing leading slash when routes are valid', function () {
+    process.env.NODE_ENV = 'development'
+    maps = createRouteMap([
+      { path: '/bar', name: 'bar', component: Bar }
+    ])
+    expect(console.warn).not.toHaveBeenCalled()
+  })
+
+  it('in production, it does not log the missing leading slash warning', function () {
+    process.env.NODE_ENV = 'production'
+    maps = createRouteMap([
+      { path: 'bar', name: 'bar', component: Bar }
+    ])
+    expect(console.warn).not.toHaveBeenCalled()
+  })
+
   describe('path-to-regexp options', function () {
     const routes = [
       { path: '/foo', name: 'foo', component: Foo },