Upgrade Gradle Wrapper and build against Java 18

[beatngu13]

EDIT: Updated based on Nicolai's comment.

Draft because this is still open for discussion.

Closes #613, #659.

Proposed commit message:

Upgrade Gradle, build against Java 18/19, improve modular tests (#613, #659 / #651)

(Yes, this change does too much, but it all hangs together.)

Updates the Gradle wrapper version from 7.4 to 7.5 because that comes
with support for Java 18, which is also added to the build pipeline.
The experimental Java version is now (for another few days), Java 19.

The modular build is properly configured to really test from the
module path.

Furthermore, replaces the archived/deprecated GitHub action
sormuras/download-jdk with oracle-actions/setup-java.

Closes: #613, #659
PR: #651

---

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Documentation (general)

• There is documentation (Javadoc and site documentation; added or updated)
• There is implementation information to describe why a non-obvious source code / solution got implemented
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Code

• Code adheres to code style, naming conventions etc.
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Contributing

• A prepared commit message exists
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[beatngu13]

Warning
Added merge-ready to see how the build behaves.

[beatngu13]

JUnit 5.9.0-RC1 is causing trouble:

/home/runner/work/junit-pioneer/junit-pioneer/src/test/java/org/junitpioneer/internal/TestExtensionContext.java:33: error: TestExtensionContext is not abstract and does not override abstract method getExecutableInvoker() in ExtensionContext
public class TestExtensionContext implements ExtensionContext {

Will exclude it from this PR, openend #652 for that purpose.

[Bukama]

Task :demoTests
EnvironmentVariablesExtensionDemo > testSet() FAILED
    org.junit.jupiter.api.extension.ExtensionConfigurationException at EnvironmentVariableUtils.java:104
        Caused by: java.lang.reflect.InaccessibleObjectException at AccessibleObject.java:354
EnvironmentVariablesExtensionDemo > testClear() FAILED
    org.junit.jupiter.api.extension.ExtensionConfigurationException at EnvironmentVariableUtils.java:104
        Caused by: java.lang.reflect.InaccessibleObjectException at AccessibleObject.java:354
EnvironmentVariablesExtensionDemo > testClearAndSet() FAILED
    org.junit.jupiter.api.extension.ExtensionConfigurationException at EnvironmentVariableUtils.java:104
        Caused by: java.lang.reflect.InaccessibleObjectException at AccessibleObject.java:354
1[85](https://github.com/junit-pioneer/junit-pioneer/runs/7347294866?check_suite_focus=true#step:4:86) 
tests completed, 3 failed, 13 skipped

We got failing tests with Java 18, seems the EnvironmentExtension needs some love

[beatngu13]

I believe it is because of this:

https://github.com/junit-pioneer/junit-pioneer/blob/main/docs/environment-variables.adoc#warnings-for-reflective-access

But why are tests passing on 17? Shouldn't the InaccessibleObjectException also occur there?

https://github.com/junit-pioneer/junit-pioneer/runs/6745721032?check_suite_focus=true#step:4:66

[beatngu13]

Now we get an error in the default locale extension with Java 19:

> Task :compileJava
D:\a\junit-pioneer\junit-pioneer\src\main\java\org\junitpioneer\jupiter\DefaultLocaleExtension.java:69: warning: [deprecation] Locale(String,String,String) in Locale has been deprecated
			return new Locale(language, country, variant);
			       ^
D:\a\junit-pioneer\junit-pioneer\src\main\java\org\junitpioneer\jupiter\DefaultLocaleExtension.java:71: warning: [deprecation] Locale(String,String) in Locale has been deprecated
			return new Locale(language, country);
			       ^
D:\a\junit-pioneer\junit-pioneer\src\main\java\org\junitpioneer\jupiter\DefaultLocaleExtension.java:73: warning: [deprecation] Locale(String) in Locale has been deprecated
			return new Locale(language);

Apparently, the Locale ctors have been deprecated in Java 19. Several alternatives exist to obtain a Locale, so I looked into Locale.Builder.

However, the impl notes from the deprecated Locale ctor says:

• Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
• For backward compatibility reasons, this constructor does not make any syntactic checks on the input.

When we switch to Locale.Builder, which does syntax checks, we change the extension's behavior (breaking change) and also get test failures:

DefaultLocaleTests
  applied on the method level
    sets the default locale using a language, a country and a variant
      java.util.IllformedLocaleException: Ill-formed variant: gb [at index 0]
    sets the default locale using a language
      java.util.IllformedLocaleException: Ill-formed language: en_EN [at index 0]

[Bukama]

I like seeing this annotation in the wild life :D

[aepfli]

me too - specially as it is my baby :D

[beatngu13]

To move on with this PR, how about excluding the update of the experimental Java version (i.e. Java 19)? I would create separate issue(s) for:

• Let the default locale extension use Locale.Builder. We do this as part of Pioneer 2.0 since the syntax checks the builder does is a breaking change.
• Afterwards, include Java 19 (or 20) in the build as experimental version.

[Bukama]

I support your suggestion

[beatngu13]

Created #658 and #659, and set experimental Java version to 18.

[beatngu13]

(Almost) all builds are green!

(That episode deserves a better rating!)

---

Jokes aside:

• The 2 failing experimental builds complain about:

  No compatible toolchains found for request filter: {languageVersion=17, vendor=any, implementation=vendor-specific} (auto-detect true, auto-download false)
  

  I think I saw that one before, will try a re-run tomorrow.
• There are still some warnings such as:

  module-info.class ignored in patch: D:\a\junit-pioneer\junit-pioneer\build\classes\java\main
  

• The modular setup needs a proper review (@nipafx 👀).

[aepfli]

Let's activate auto downloading toolchains for Gradle - this should fix the issue

[aepfli]

[beatngu13]

@aepfli thx for the fix!

One more thing:

junit-pioneer/.github/workflows/build.yml

Line 155 in e68e91d

# but execute the build on the experimental version

junit-pioneer/.github/workflows/build.yml

Line 170 in e68e91d

# The Java Version Gradle will be using for execution

I find these comments a bit confusing, both mention "execution" but use different Java version. Maybe:

# Gradle doesn't work with JDK EA builds, so we launch it with a supported Java version,
# but set the Gradle toolchain to use the experimental version

WDYT?

[nipafx]

This PR fixes the failing build (shakes fist at @sormuras), so we should move forward with it. Here's a review, I will take a look at the linked issues soon, to see what else needs to be addressed.

[nipafx]

Note that I also included the Java 19 upgrade (#659) into this PR by simply ignoring the deprecation warnings.

Updated commit message:

Upgrade Gradle, build against Java 18/19, improve modular tests (#613, #659 / #651)

(Yes, this change does too much, but it all hangs together.)

Updates the Gradle wrapper version from 7.4 to 7.5 because that comes
with support for Java 18, which is also added to the build pipeline.
The experimental Java version is now (for another few days), Java 19.

The modular build is properly configured to really test from the
module path.

Furthermore, replaces the archived/deprecated GitHub action
sormuras/download-jdk with oracle-actions/setup-java.

Closes: #613, #659
PR: #651