Upgrading react-scripts from 3.2.0 to 3.4.0 will cause routing URL behave differently when "homepage" is set in Dev mode

[tkforce]

Describe the bug

Upgrading react-scripts from 3.2.0 to 3.4.0 will cause routing URL behave differently when "homepage" is set in Dev mode.

With hompage:"/my/dir" set in my package.json and using React router component <Link to="/about">About</Link> to do the routing, different version will have different behavior on the url generated in <a href="xxx"> :

v3.2.0 -> <a href="https://github.com/about">
v3.4.0 -> <a href="https://github.com/my/dir/about">

But it seems to be only affecting dev version of the application, production build is always pointing to <a href="https://github.com/my/dir/about">

Did you try recovering your dependencies?

Yes

Which terms did you search for in User Guide?

homepage, react-scripts, 3.4.0, change log

Environment

(paste the output of the command here.)

Steps to reproduce

(Write your steps here:)

1. install react-scripts 3.2.0
2. set homepage:"/my/dir" in package.json
3. add <Link to="/about">About</Link> from react-router to the project
4. npm start
5. inspect this element in browser, it will have different href in different react-scripts version
   v3.2.0 -> <a href="https://github.com/about">
v3.4.0 -> <a href="https://github.com/my/dir/about">

Expected behavior

Should behave the same as the previous version.

Actual behavior

Inspect this element in browser, it will have different href in different react-scripts version
v3.2.0 -> <a href="https://github.com/about">
v3.4.0 -> <a href="https://github.com/my/dir/about">

Reproducible demo

(Paste the link to an example project and exact instructions to reproduce the issue.)

[mbochynski]

This change was made on purpose. You can check details here: #7259 So probably you will need to change your config. The change broke my setup too. For me setting PUBLIC_URL by hand in dev and during the build make the job.

[jamesplease]

This comment may help you @tkforce

[tkforce]

@jamesplease Thanks for explaining this issue in detail, really appreciate!

In my cases we only use homepage rather then PUBLIC_URL, do you mind elaborate the difference between them and when to use which (I did read through docs but still not quit fully understood)?

My observation is that with homepage:/my-app in v3.4.0, at lease url in dev and prod is aligned without any extra manipulation.
DEV: localhost:3000/my-app/xxx
PROD: some-public-domain.com/my-app/xxx

while in v3.3.2
DEV: localhost:3000/xxx
PROD: some-public-domain.com/my-app/xxx

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