fix diagnostics when visiting JDT provided files

Change the URI used to refer to a JDT provided file to the one that
was used to generate it in the first place.

Author: gnuemacscoin

eglot-java.el

@@ -1459,6 +1459,23 @@ DESTINATION-DIR is the directory where the LSP server will be installed."
 
 (defvar eglot-java-jdt-uri-handling-patch-applied nil "Whether or not JDT uri handling is already patched.")
 
+(defun eglot-java--wrap-eglot--path-to-uri (original-fn &rest args)
+  "Advice to set up proper diagnostics in server-generated source files.
+ARGS is a list with one element, a file path. If that path specifies a java
+file inside a `.eglot-java' directory, recover its `jdt://' URI from
+within the matching `.metadata' file. Otherwise, call ORIGINAL-FN."
+  (let* ((path (car args))
+         (directory-path (file-name-directory path)))
+    (if (not (and (string= "java" (file-name-extension path))
+                  (string= ".eglot-java" (file-name-nondirectory (directory-file-name directory-path)))))
+        (apply original-fn args)
+      (let* ((metadata-file-path (format "%s.%s.metadata" directory-path (file-name-base path))))
+        (if (not (file-readable-p metadata-file-path))
+            (apply original-fn args)
+          (with-temp-buffer
+            (insert-file-contents metadata-file-path)
+            (buffer-string)))))))
+
 (defun eglot-java--wrap-legacy-eglot--path-to-uri (original-fn &rest args)
   "Hack until eglot is updated.
 ARGS is a list with one element, a file path or potentially a URI.
@@ -1480,7 +1497,9 @@ handle it. If it is not a jar call ORIGINAL-FN."
       (apply original-fn args))))
 
 (defun eglot-java--jdthandler-patch-eglot ()
-  "Patch old versions of Eglot to work with Jdthandler."
+  "Patch Eglot path-uri conversion functions.
+Patch old versions of Eglot to work with Jdthandler.
+Patch all versions to work with files from `java/classFileContents'."
   (interactive) ;; TODO Remove when eglot is updated in melpa
   ;; See also https://debbugs.gnu.org/cgi/bugreport.cgi?bug=58790
   ;; See also https://git.savannah.gnu.org/gitweb/?p=emacs.git;a=blob;f=lisp/progmodes/eglot.el#l1558
@@ -1489,7 +1508,9 @@ handle it. If it is not a jar call ORIGINAL-FN."
               (<= 29 emacs-major-version))
     (advice-add 'eglot--path-to-uri :around #'eglot-java--wrap-legacy-eglot--path-to-uri)
     (advice-add 'eglot--uri-to-path :around #'eglot-java--wrap-legacy-eglot--uri-to-path)
-    (message "[eglot-java--jdthandler-patch-eglot] Eglot successfully patched.")))
+    (message "[eglot-java--jdthandler-patch-eglot] Eglot successfully patched."))
+  (unless (advice-member-p #'eglot-java--wrap-eglot--path-to-uri 'eglot-path-to-uri)
+    (advice-add 'eglot-path-to-uri :around #'eglot-java--wrap-eglot--path-to-uri)))
 
 (defun eglot-java--find-server ()
   "Find the LSP server of type eglot-java-eclipse-jdt for the