jdtls only checks the syntax of a Java file outside every module's source
folders (or outside any imported project) and answers navigation with
nothing. The editor then said only "Cannot find declaration to go to", and
the server's explanation was a warning squiggle on line 1.
- A banner above the editor explains it while the server reports it, for
jdtls (not on the classpath of a project / non-project file), gopls (no
package, build constraints — this replaces the Go-only banner) and
rust-analyzer (unlinked file). For Java it offers the Maven / Gradle reload
when available.
- Go to Declaration / Implementation / Type Declaration that finds nothing
in such a file gives the reason in its hint.
Fixes#827