nginx, how do I debug which location directive was applied?

Three location directives, one at a time, were commented out and experimented.

#Explicit access to the root website, redirect to main page (adapt as needed)
location=/{
  return301/wiki/main page;
}

#Handling for the article path (pretty URLs)
location/wiki/{
  rewrite.*/index.php;
}

#Location for wiki's entry points
location~^/(index|load|api|thumb|opensearch_desc|rest|img_auth)\.php${
  include/etc/nginx/fastcgi_params;
  fastcgi_param SCRIPT_FILENAME$ document_root$fastcgi_script_name;
  fastcgi_pass 127.0.0.1:9000;# or whatver port your PHP-FPM lists on
}

Comment out only location=/.

http://example.com to 404 Not Found.
Redirect to http://example.com/wiki/ main page does not occur.

http://example.com/wiki/ main page is displayed successfully.
http://example.com/index.php?title=Main Page displays the main page successfully.

Comment out only location/wiki/.

http://example.com is
404 Not Found after redirecting to http://example.com/wiki/ main page.

http://example.com/wiki/ main page is also 404 Not Found.

http://example.com/index.php?title=main page displays the page.

location~^/(index|load|api|thumb|opensearch_desc|rest|img_auth)\.php$ only.

http://example.com
http://example.com/wiki/ main page
http://example.com/index.php?title=Main Page
404 Not Found for all three URLs.

The order in which the location directives are applied is

There is no doubt about the order in
(Because the number of URLs increasing gradually becomes 404 Not Found)

In addition to observing symptoms while commenting out,
Please let me know if anyone knows how to clearly understand which directives were applied in which order.

The redirected URL is

http://example.com
↓ External Redirect
http://example.com/wiki/ main page
↓ Internal Redirect
http://example.com/index.php?title=Main Page

I thought it was a movement like this, but

http://example.com
↓ External Redirect
http://example.com/wiki/ main page
↓ Internal Redirect
http://example.com/index.php

It seems to be moving like this

REQUEST_URI contains the text /wiki/main page and appears to be used in index.php.
$_SERVER['REQUEST_URI'] is not used in the index.php source, but it appears to be used in one of the files require in index.php.

Finally
If you are internally redirected to http://example.com/index.php,
The value of REQUEST_URI should be /index.php?
Why is the intermediate /wiki/main page adopted?

Can someone tell me how the REQUEST_URI is determined if it is redirected multistagely?
I think it's probably the difference between external and internal redirect, but I can't find the document on my own.

How to print any log message to nginx.

/etc/nginx/nginx.conf
Added one line below to .

log_format mydebug"[MYDEBUG][$time_local]$request_uri,dbg1:$dbg1dbg2:$dbg2dbg3:$dbg3";

(mydebug or $dbg1 is any string)

/etc/nginx/conf.d/mediawiki.conf
Add set~~ and access_log~~ to .

#Location for wiki's entry points
location~^/(index|load|api|thumb|opensearch_desc|rest|img_auth)\.php${

  set$dbg1$msec;
  access_log/var/log/nginx/mydebug.log mydebug;

  include/etc/nginx/fastcgi_params;
  fastcgi_param SCRIPT_FILENAME$ document_root$fastcgi_script_name;
  fastcgi_pass 127.0.0.1:9000;# or whatver port your PHP-FPM lists on
}

#Handling for the article path (pretty URLs)
location/wiki/{

  set$dbg2$msec;
  access_log/var/log/nginx/mydebug.log mydebug;

  rewrite.*/index.php;
}

#Explicit access to the root website, redirect to main page (adapt as needed)
location=/{

  set$dbg3$msec;
  access_log/var/log/nginx/mydebug.log mydebug;

  return301/wiki/main page;
}

Check mydebug.log to see the following logs:

[MYDEBUG] [17/Jun/2021:09:51:09+0900] /,dbg1:dbg2:dbg3:1623891069.090
[MYDEBUG][17/Jun/2021:51:09+0900]/wiki/%E3%83%A1%E3%82%E3%E3%83%B3%E3%83%E3%83%BC%E3%82%B8,dbg1:1623891069.100dbg2:1623891069.100dbg3:

$request_uri is /,
dbg3 logs with timestamps first.

The location=/ directive is confirmed to have been applied first.

$request_uri is logged in /wiki/%E3%83%A1%E3%82%A4%E3%E3%83%B3%E3%83%E3%83%B8 (/wiki/main page), dbg1 and dbg2.

The dbg1 and dbg2 timestamps are the same.
dbg1 or dbg2 I don't know which comes first, but it seems to be processed continuously.

I expected 3 lines of log to be logged, but only 2 lines.

Commenting out the access_log~ of dbg2 does not affect the log output.
Only access_log~ on the dbg1 side is adopted, and access_log~ on the dbg2 side is not used.

For rewrite (internal redirect), access_log is likely to be logged in the location directive that finally arrived.

http://example.com
↓
http://example.com/wiki/ main page
↓
http://example.com/index.php

It was a mistake to recognize that it was a series of actions.

Browser:Request to http://example.com
Server: http://example.com/wiki/ main page response.

This is the end of the first request.

Browser: Request to http://example.com/wiki/ main page
Server: I managed to respond to html.

In the second request, REQUEST_URI becomes /wiki/main page because you are accessing http://example.com/wiki/ main page.