From 6404fc7869103e84c7f9b0c0f8ac691ccc244288 Mon Sep 17 00:00:00 2001
From: Blaine Kasten <blainekasten@gmail.com>
Date: Fri, 10 Jul 2020 13:55:11 -0500
Subject: [PATCH] fix(gatsby-link): Do not crash in unit tests when globals are
 undefined (#25608)

* fix(gatsby-link): Do not crash in unit tests when globals are undefined

* wrap in production checks

* different approach

* Revert "different approach"

This reverts commit 91a894b13ccdf794575237aee0d7c733ad5f8414.
---
 packages/gatsby-link/src/__tests__/index.js |  4 ++--
 packages/gatsby-link/src/index.js           | 21 ++++++++++++++++++---
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/packages/gatsby-link/src/__tests__/index.js b/packages/gatsby-link/src/__tests__/index.js
index 82eaefb5c9dc9..c2a4b62956937 100644
--- a/packages/gatsby-link/src/__tests__/index.js
+++ b/packages/gatsby-link/src/__tests__/index.js
@@ -94,8 +94,8 @@ describe(`<Link />`, () => {
   })
 
   it(`does not fail with missing __BASE_PATH__`, () => {
-    global.__PATH_PREFIX__ = ``
-    global.__BASE_PATH__ = undefined
+    delete global.__PATH_PREFIX__
+    delete global.__BASE_PATH__
 
     const source = createMemorySource(`/active`)
 
diff --git a/packages/gatsby-link/src/index.js b/packages/gatsby-link/src/index.js
index 052a3d98a85eb..7206979c63e8d 100644
--- a/packages/gatsby-link/src/index.js
+++ b/packages/gatsby-link/src/index.js
@@ -9,7 +9,7 @@ export { parsePath }
 
 const isAbsolutePath = path => path?.startsWith(`/`)
 
-export function withPrefix(path, prefix = __BASE_PATH__) {
+export function withPrefix(path, prefix = getGlobalBasePrefix()) {
   if (!isLocalLink(path)) {
     return path
   }
@@ -17,13 +17,28 @@ export function withPrefix(path, prefix = __BASE_PATH__) {
   if (path.startsWith(`./`) || path.startsWith(`../`)) {
     return path
   }
-  const base = prefix ?? __PATH_PREFIX__ ?? `/`
+  const base = prefix ?? getGlobalPathPrefix() ?? `/`
 
   return `${base?.endsWith(`/`) ? base.slice(0, -1) : base}${
     path.startsWith(`/`) ? path : `/${path}`
   }`
 }
 
+// These global values are wrapped in typeof clauses to ensure the values exist.
+// This is especially problematic in unit testing of this component.
+const getGlobalPathPrefix = () =>
+  process.env.NODE_ENV !== `production`
+    ? typeof __PATH_PREFIX__ !== `undefined`
+      ? __PATH_PREFIX__
+      : undefined
+    : __PATH_PREFIX__
+const getGlobalBasePrefix = () =>
+  process.env.NODE_ENV !== `production`
+    ? typeof __BASE_PATH__ !== `undefined`
+      ? __BASE_PATH__
+      : undefined
+    : __BASE_PATH__
+
 const isLocalLink = path =>
   path &&
   !path.startsWith(`http://`) &&
@@ -31,7 +46,7 @@ const isLocalLink = path =>
   !path.startsWith(`//`)
 
 export function withAssetPrefix(path) {
-  return withPrefix(path, __PATH_PREFIX__)
+  return withPrefix(path, getGlobalPathPrefix())
 }
 
 function absolutify(path, current) {