Prevent path prefix from being incorrectly applied

packages/gatsby/cache-dir/__tests__/loader.js

@@ -2,6 +2,13 @@ import loader from "../loader.js"
 
 describe(`Loader`, () => {
   beforeEach(() => {
+    delete global.__PATH_PREFIX__
+    delete global.__PREFIX_PATHS__
+
+    // Workaround for Node 6 issue: https://github.com/facebook/jest/issues/5159
+    if (global.hasOwnProperty(`__PATH_PREFIX__`)) global.__PATH_PREFIX__ = undefined
+    if (global.hasOwnProperty(`__PREFIX_PATHS__`)) global.__PREFIX_PATHS__ = undefined
+
     loader.empty()
     loader.addPagesArray([
       {
@@ -68,3 +75,72 @@ describe(`Loader`, () => {
     expect(loader.getResources()).toMatchSnapshot()
   })
 })
+
+describe(`Loader path prefixing`, () => {
+  let pagesArray
+
+  beforeEach(() => {
+    delete global.__PATH_PREFIX__
+    delete global.__PREFIX_PATHS__
+
+    // Workaround for Node 6 issue: https://github.com/facebook/jest/issues/5159
+    if (global.hasOwnProperty(`__PATH_PREFIX__`)) global.__PATH_PREFIX__ = undefined
+    if (global.hasOwnProperty(`__PREFIX_PATHS__`)) global.__PREFIX_PATHS__ = undefined
+
+    pagesArray = [
+      {
+        path: `/about/`,
+        componentChunkName: `page-component---src-pages-test-js`,
+        jsonName: `about.json`,
+      },
+      {
+        path: `/about/me/`,
+        componentChunkName: `page-component---src-pages-test-js`,
+        jsonName: `about-me.json`,
+      },
+    ]
+
+    loader.empty()
+  })
+
+  test(`Path prefix present and enabled`, () => {
+    global.__PATH_PREFIX__ = `/foo`
+    global.__PREFIX_PATHS__ = true
+    loader.addPagesArray(pagesArray)
+    loader.enqueue(`/foo/about/`)
+    expect(loader.has(`/about/`)).toEqual(true)
+    expect(loader.has(`/foo/about/`)).toEqual(false)
+  })
+
+  test(`Path prefix present but not enabled`, () => {
+    global.__PATH_PREFIX__ = `/foo`
+    delete global.__PREFIX_PATHS__
+    loader.addPagesArray(pagesArray)
+
+    // don't enqueue prefixed paths
+    loader.enqueue(`/foo/about/`)
+    expect(loader.has(`/about/`)).toEqual(false)
+    expect(loader.has(`/foo/about/`)).toEqual(false)
+
+    // do enqueue unprefixed paths
+    loader.enqueue(`/about/`)
+    expect(loader.has(`/about/`)).toEqual(true)
+    expect(loader.has(`/foo/about/`)).toEqual(false)
+  })
+
+  test(`Path prefix missing but enabled`, () => {
+    delete global.__PATH_PREFIX__
+    global.__PREFIX_PATHS__ = true
+    loader.addPagesArray(pagesArray)
+
+    // don't enqueue prefixed paths
+    loader.enqueue(`/foo/about/`)
+    expect(loader.has(`/about/`)).toEqual(false)
+    expect(loader.has(`/foo/about/`)).toEqual(false)
+
+    // do enqueue unprefixed paths
+    loader.enqueue(`/about/`)
+    expect(loader.has(`/about/`)).toEqual(true)
+    expect(loader.has(`/foo/about/`)).toEqual(false)
+  })
+})

packages/gatsby/cache-dir/__tests__/strip-prefix.js

@@ -0,0 +1,23 @@
+const stripPrefix = require(`../strip-prefix`).default
+
+describe(`strip-prefix`, () => {
+  it(`strips a prefix`, () => {
+    expect(stripPrefix(`/foo/bar/`, `/foo`)).toBe(`/bar/`)
+  })
+
+  it(`strips first instance only`, () => {
+    expect(stripPrefix(`/foo/foo/bar/`, `/foo`)).toBe(`/foo/bar/`)
+  })
+
+  it(`ignores prefix appearing elsewhere in the string`, () => {
+    expect(stripPrefix(`/foo/bar/`, `bar`)).toBe(`/foo/bar/`)
+  })
+
+  it(`ignores a non-existent prefix`, () => {
+    expect(stripPrefix(`/bar`, `/foo`)).toBe(`/bar`)
+  })
+
+  it(`returns input str if no prefix is provided`, () => {
+    expect(stripPrefix(`/bar`)).toBe(`/bar`)
+  })
+})

packages/gatsby/cache-dir/find-page.js

@@ -1,12 +1,14 @@
 // TODO add tests especially for handling prefixed links.
 import { matchPath } from "react-router-dom"
+import stripPrefix from "./strip-prefix"
 
 const pageCache = {}
 
 module.exports = (pages, pathPrefix = ``) => rawPathname => {
   let pathname = decodeURIComponent(rawPathname)
+
   // Remove the pathPrefix from the pathname.
-  let trimmedPathname = pathname.slice(pathPrefix.length)
+  let trimmedPathname = stripPrefix(pathname, pathPrefix)
 
   // Remove any hashfragment
   if (trimmedPathname.split(`#`).length > 1) {

packages/gatsby/cache-dir/loader.js

@@ -1,6 +1,7 @@
 import React, { createElement } from "react"
 import pageFinderFactory from "./find-page"
 import emitter from "./emitter"
+import stripPrefix from "./strip-prefix"
 let findPage
 
 let syncRequires = {}
@@ -14,6 +15,7 @@ let pages = []
 // we load all resources for likely-to-be-visited paths.
 let pathArray = []
 let pathCount = {}
+let pathPrefix = ``
 let resourcesArray = []
 let resourcesCount = {}
 const preferDefault = m => (m && m.default) || m
@@ -153,12 +155,15 @@ const queue = {
     resourcesCount = {}
     resourcesArray = []
     pages = []
+    pathPrefix = ``
   },
   addPagesArray: newPages => {
     pages = newPages
-    let pathPrefix = ``
-    if (typeof __PREFIX_PATHS__ !== `undefined`) {
-      pathPrefix = __PATH_PREFIX__
+    if (
+      typeof __PREFIX_PATHS__ !== `undefined` &&
+      typeof __PATH_PREFIX__ !== `undefined`
+    ) {
+      if (__PREFIX_PATHS__ === true) pathPrefix = __PATH_PREFIX__
     }
     findPage = pageFinderFactory(newPages, pathPrefix)
   },
@@ -168,9 +173,10 @@ const queue = {
   addProdRequires: prodRequires => {
     asyncRequires = prodRequires
   },
-  dequeue: path => pathArray.pop(),
-  enqueue: path => {
+  dequeue: () => pathArray.pop(),
+  enqueue: rawPath => {
     // Check page exists.
+    const path = stripPrefix(rawPath, pathPrefix)
     if (!pages.some(p => p.path === path)) {
       return false
     }

packages/gatsby/cache-dir/strip-prefix.js

@@ -0,0 +1,9 @@
+/**
+ * Remove a prefix from a string. Return the input string if the given prefix
+ * isn't found.
+ */
+
+export default (str, prefix = ``) => {
+  if (str.substr(0, prefix.length) === prefix) return str.slice(prefix.length)
+  return str
+}