JavaCompile and Test tasks silently ignore explicit executable if it does not exist

[alllex]

When resolving which toolchain to use for the java compiler in the JavaCompile task or for the launcher in the Test task, there is a priority that is given to an executable path explicitly set via fork options. However, if a user makes a mistake by providing a wrong path, then the provided value is silently ignored and the current toolchain is used to execute the work.

At the very least, the user should be warned about this. However, being strict about this may be better, as this can be overlooked when tasks are running on CI and for some reason it was required to use an explicit path, rather than resolving a toolchain.

gradle/subprojects/language-java/src/main/java/org/gradle/api/tasks/compile/JavaCompile.java

Lines 254 to 262 in c1e31d6

	final String customExecutable = getOptions().getForkOptions().getExecutable();
	if (customExecutable != null) {
	final File executable = new File(customExecutable);
	if (executable.exists()) {
	// Relying on the layout of the toolchain distribution: <JAVA HOME>/bin/<executable>
	File parentJavaHome = executable.getParentFile().getParentFile();
	return new SpecificInstallationToolchainSpec(objectFactory, parentJavaHome);
	}
	}