feat(gatsby): Add support for relative links

packages/gatsby-link/src/index.js

@@ -1,12 +1,20 @@
 import PropTypes from "prop-types"
 import React from "react"
-import { Link } from "@reach/router"
+import { Link, Location } from "@reach/router"
+import { resolve } from "@reach/router/lib/utils"
 
 import { parsePath } from "./parse-path"
 
 export { parsePath }
 
+function isRelativePath(path) {
+  return /^\.{1,2}\//.test(path)
+}
+
 export function withPrefix(path) {
+  if (isRelativePath(path)) {
+    return normalizePath(path)
+  }
   return normalizePath(
     [
       typeof __BASE_PATH__ !== `undefined` ? __BASE_PATH__ : __PATH_PREFIX__,
@@ -16,13 +24,23 @@ export function withPrefix(path) {
 }
 
 export function withAssetPrefix(path) {
-  return [__PATH_PREFIX__].concat([path.replace(/^\//, ``)]).join(`/`)
+  return isRelativePath(path)
+    ? path
+    : [__PATH_PREFIX__].concat([path.replace(/^\//, ``)]).join(`/`)
 }
 
 function normalizePath(path) {
   return path.replace(/\/+/g, `/`)
 }
 
+function absolutify(path, current) {
+  // If it's already absolute, return as-is
+  if (!isRelativePath(path)) {
+    return path
+  }
+  return resolve(path, current)
+}
+
 const NavLinkPropTypes = {
   activeClassName: PropTypes.string,
   activeStyle: PropTypes.object,
@@ -131,59 +149,73 @@ class GatsbyLink extends React.Component {
       /* eslint-enable no-unused-vars */
       ...rest
     } = this.props
-
     const LOCAL_URL = /^\/(?!\/)/
-    if (process.env.NODE_ENV !== `production` && !LOCAL_URL.test(to)) {
+    const isRelative = isRelativePath(to)
+    if (
+      process.env.NODE_ENV !== `production` &&
+      !LOCAL_URL.test(to) &&
+      !isRelative
+    ) {
       console.warn(
         `External link ${to} was detected in a Link component. Use the Link component only for internal links. See: https://gatsby.dev/internal-links`
       )
     }
 
-    const prefixedTo = withPrefix(to)
-
     return (
-      <Link
-        to={prefixedTo}
-        state={state}
-        getProps={getProps}
-        innerRef={this.handleRef}
-        onMouseEnter={e => {
-          if (onMouseEnter) {
-            onMouseEnter(e)
-          }
-          ___loader.hovering(parsePath(to).pathname)
-        }}
-        onClick={e => {
-          if (onClick) {
-            onClick(e)
-          }
-
-          if (
-            e.button === 0 && // ignore right clicks
-            !this.props.target && // let browser handle "target=_blank"
-            !e.defaultPrevented && // onClick prevented default
-            !e.metaKey && // ignore clicks with modifier keys...
-            !e.altKey &&
-            !e.ctrlKey &&
-            !e.shiftKey
-          ) {
-            e.preventDefault()
-
-            let shouldReplace = replace
-            const isCurrent = encodeURI(to) === window.location.pathname
-            if (typeof replace !== `boolean` && isCurrent) {
-              shouldReplace = true
-            }
-
-            // Make sure the necessary scripts and data are
-            // loaded before continuing.
-            navigate(to, { state, replace: shouldReplace })
-          }
-
-          return true
+      <Location>
+        {({ location }) => {
+          const prefixedTo = isRelative
+            ? absolutify(to, location.pathname)
+            : withPrefix(to)
+
+          return (
+            <Link
+              to={prefixedTo}
+              state={state}
+              getProps={getProps}
+              innerRef={this.handleRef}
+              onMouseEnter={e => {
+                if (onMouseEnter) {
+                  onMouseEnter(e)
+                }
+                ___loader.hovering(parsePath(to).pathname)
+              }}
+              onClick={e => {
+                if (onClick) {
+                  onClick(e)
+                }
+
+                if (
+                  e.button === 0 && // ignore right clicks
+                  !this.props.target && // let browser handle "target=_blank"
+                  !e.defaultPrevented && // onClick prevented default
+                  !e.metaKey && // ignore clicks with modifier keys...
+                  !e.altKey &&
+                  !e.ctrlKey &&
+                  !e.shiftKey
+                ) {
+                  e.preventDefault()
+
+                  let shouldReplace = replace
+                  const isCurrent = encodeURI(to) === window.location.pathname
+                  if (typeof replace !== `boolean` && isCurrent) {
+                    shouldReplace = true
+                  }
+                  // Make sure the necessary scripts and data are
+                  // loaded before continuing.
+                  window.___navigate(prefixedTo, {
+                    state,
+                    replace: shouldReplace,
+                  })
+                }
+
+                return true
+              }}
+              {...rest}
+            />
+          )
         }}
-        {...rest}
-      />
+      </Location>
     )
   }
 }

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

@@ -24,4 +24,8 @@ describe(`strip-prefix`, () => {
   it(`returns input str if no prefix is provided`, () => {
     expect(stripPrefix(`/bar`)).toBe(`/bar`)
   })
+
+  it(`returns "/" if str equals prefix`, () => {
+    expect(stripPrefix(`/bar`, `/bar`)).toBe(`/bar`)
+  })
 })

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

@@ -17,6 +17,16 @@ const trimPathname = rawPathname => {
   return trimmedPathname
 }
 
+function absolutify(path) {
+  // If it's already absolute, return as-is
+  if (!/^\.{1,2}\/(?!\/)/.test(path)) {
+    return path
+  }
+  // Calculate path relative to current location, adding a trailing slash to
+  // match behavior of @reach/router
+  return new URL(path, window.location.href.replace(/([^/])$/, `$1/`)).pathname
+}
+
 /**
  * Set list of matchPaths
  *
@@ -55,8 +65,7 @@ export const findMatchPath = rawPathname => {
 // Or if `match-paths.json` contains `{ "/foo*": "/page1", ...}`, then
 // `/foo?bar=far` => `/page1`
 export const findPath = rawPathname => {
-  const trimmedPathname = trimPathname(rawPathname)
-
+  const trimmedPathname = trimPathname(absolutify(rawPathname))
   if (pathCache.has(trimmedPathname)) {
     return pathCache.get(trimmedPathname)
   }
@@ -80,7 +89,7 @@ export const findPath = rawPathname => {
  * @return {string}
  */
 export const cleanPath = rawPathname => {
-  const trimmedPathname = trimPathname(rawPathname)
+  const trimmedPathname = trimPathname(absolutify(rawPathname))
 
   let foundPath = trimmedPathname
   if (foundPath === `/index.html`) {

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

@@ -3,15 +3,17 @@
  * isn't found.
  */
 
-export default (str, prefix = ``) => {
+export default function stripPrefix(str, prefix = ``) {
   if (!prefix) {
     return str
   }
 
-  prefix += `/`
+  if (str === prefix) {
+    return `/`
+  }
 
-  if (str.substr(0, prefix.length) === prefix) {
-    return str.slice(prefix.length - 1)
+  if (str.startsWith(`${prefix}/`)) {
+    return str.slice(prefix.length)
   }
 
   return str