Try JDK 19

[basil]

No description provided.

[basil]

Only 4 test failures, better than I was expecting. The three from display-url-api are all false positives caused by an outdated build toolchain, fixed in jenkinsci/display-url-api-plugin#159.

[basil]

The hudson.plugins.git.browser.AssemblaWebDoCheckURLTest#testInitialChecksOnRepoUrl is interesting and can be reproduced easily on Java 19. It starts happening after openjdk/jdk#7181 and can be reproduced even on Java 11 by adding

diff --git a/core/src/main/java/hudson/util/FormValidation.java b/core/src/main/java/hudson/util/FormValidation.java
index 931e47ccf0..e733a77c73 100644
--- a/core/src/main/java/hudson/util/FormValidation.java
+++ b/core/src/main/java/hudson/util/FormValidation.java
@@ -471,6 +471,7 @@ public abstract class FormValidation extends IOException implements HttpResponse
             if (con == null) { // TODO is this even permitted by URL.openConnection?
                 throw new IOException(url.toExternalForm());
             }
+            con.setRequestProperty("Accept", "*/*");
             return new BufferedReader(
                 new InputStreamReader(con.getInputStream(), getCharset(con)));
         }

This should be fine but for whatever reason an accept header of */* rather than text/html causes the server to start spitting out a 404 instead of a 200. This can even be seen with curl(1):

$ curl --head --header "Accept: text/html" https://app.assembla.com/login
HTTP/2 200 
[…]
$
$ curl --head --header "Accept: */*" https://app.assembla.com/login
HTTP/2 404 
[…]

This is hardly our fault and I do not think there is anything the Jenkins code should be doing differently here. If anything I would just exclude this test.

[basil]

For whatever reason the above error goes away when using the native Java 11 HTTP client as in jenkinsci/jenkins#7508.

[basil]

I have learned everything I want to learn from this exercise.