CASE 1. Try and inherit doc from a compiled element, such as `java.lang.Object`

Source:
package po;

/**
 * Class O.
 */
public class O {
    private O() { }

    /**
     * Before.
     * {@inheritDoc}
     * After.
     *
     * @param other the other
     * @return the result
     */
    @Override
    public boolean equals(Object other) {
        return super.equals(other);
    }
}

Output: no diagnostic, and this in the generated output:
public boolean equals(Object other)
Before. After.
Overrides:
equals in class Object

Note: nothing between "Before." and "After."

Preferred behavior would be to get a distinct warning or error in these different cases:
1. the element was found in a class file, so the source was not available
2. the element was found in a source file, but there was no comment for the element
3. the element was found in a source file, and there was a comment, but the relevant part of the comment was empty.


CASE 2. Separate end user libraries.

Library A declares a class A with a method.
Library B declares a class B that extends A, overrides the method, and uses `{@inheritDoc}`

Generate docs for A, then:
2.1 Generate docs for B, A not provided ... gives compilation error as expected
2.2 Generate docs for B, A on source path ... finds A's source and comments, but does not link
2.3 Generate docs for B, A on classpath... finds A classes, but inheritDoc is quiet no-op, and no link (same as CASE 1)
2.4 Generate docs for B, A with -linkoffline ... gives compilation error as expected
2.5 Generate docs for B, A on source path and with -linkoffline: works as expected, finds A's source and comments, and links
2.6 Generate docs for B, A on class path and with -linkoffline: finds A classes, but inheritDoc is quiet no-op, and links


CASE 3: Same as case 1, but also using --patch-module to provide partial source for java.base

3.1 put po on sourcepath, use --patch-module for java.base

result: fails to find files for po
Possible cause: confusion between internal module (source) path and explicit sourcepath

3.2 list po files on command line

result: works as expected: finds O.java and source for Object.java, inherits doc comment correctly and generates expected links