fix: correctly calculate path when pathMatch is empty string (vuejs#3106)

Author: adi-zz

Diff for: src/util/params.js

@@ -20,7 +20,8 @@ export function fillParams (
       (regexpCompileCache[path] = Regexp.compile(path))
 
     // Fix #2505 resolving asterisk routes { name: 'not-found', params: { pathMatch: '/not-found' }}
-    if (params.pathMatch) params[0] = params.pathMatch
+    // `params.pathMatch === ''` fixes #3106 so that you can work with location descriptor object having params.pathMatch equal to empty string
+    if (params.pathMatch || params.pathMatch === '') params[0] = params.pathMatch
 
     return filler(params, { pretty: true })
   } catch (e) {

Diff for: test/unit/specs/create-matcher.spec.js

@@ -84,4 +84,14 @@ describe('Creating Matcher', function () {
     const { params } = match({ path: '/not-found' }, routes[0])
     expect(params).toEqual({ pathMatch: '/not-found' })
   })
+
+  it('calculates correctly and without warning the path of a partial asterisk route with a default param name and pathMatch empty string', function () {
+    process.env.NODE_ENV = 'development'
+    const { path } = match(
+      { name: 'error', params: { pathMatch: '' }},
+      routes[0]
+    )
+    expect(console.warn).not.toHaveBeenCalled()
+    expect(path).toEqual('/error/')
+  })
 })