fix(umi-build-dev): dynamic import code splitting

[sorrycc]

规则

• dynamicLevel 默认为 1
• 根节点下 path 为 / 的 route 如果有 routes，则 dynamicLevel 为 2

例子

无 layout

+ pages
  - a.js
  - b.js
  + c
    - _layout.js
    - c1.js
    - c2.js

note:

• dynamicLevel 为 1
• 拆 a.js、b.js、c.js（包含 c1、c2 及其 _layout.js）

有 layout

+ layouts/index.js
+ pages
  - a.js
  - b.js
  + c
    - _layout.js
    - c1.js
    - c2.js

note:

• dynamicLevel 为 2
• layouts/index.js 会合并到 common-umi 里
• 拆 a.js、b.js、c.js（包含 c1、c2 及其 _layout.js）

多 layout

[
  { path: '/login' },
  { path: '/', routes: [
    { path: '/a' },
    { path: '/b' },
    { path: '/c', routes: [
      { path: '/c1' },
      { path: '/c2' },
    ] },
  ]},
]

• dynamicLevel 为 2
• 拆 /login 和 /，由于有差异，所以不会自动合并到 common-umi
• 拆 a.js、b.js、c.js（包含 c1、c2 及其 _layout.js）

[coveralls]

Pull Request Test Coverage Report for Build 385

• 8 of 12 (66.67%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 19.651%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/umi-build-dev/src/getWebpackConfig.js	0	4	0.0%

Files with Coverage Reduction	New Missed Lines	%
packages/umi-build-dev/src/getWebpackConfig.js	1	0.0%

Totals
Change from base Build 381:	0.3%
Covered Lines:	429
Relevant Lines:	2448

---

💛 - Coveralls