Fix #124: Move to LSP char positions exactly according to spec

* eglot-tests.el (issue-124): New test.

* eglot.el (eglot--lsp-char-to-column): New helper.
(eglot--lsp-position-to-point): Use eglot--lsp-char-to-column.

* fixtures/utf16.cpp: New test fixture

eglot-tests.el

@@ -600,6 +600,15 @@ Pass TIMEOUT to `eglot--with-timeout'."
     (should-not (eglot--server-capable :foobarbaz))
     (should-not (eglot--server-capable :textDocumentSync :foobarbaz))))
 
+
+(ert-deftest issue-124 ()
+  "Test LSP's UTF-16 quirks."
+  (with-current-buffer (find-file-no- "fixtures/utf16.cpp")
+    (should (eql (eglot--lsp-position-to-point '(:character 8 :line 2)) 22))
+    (should (eql (eglot--lsp-position-to-point '(:character 19 :line 2)) 33))
+    (should (eql (eglot--lsp-position-to-point '(:character 50 :line 2)) 63))
+    (should (eql (eglot--lsp-position-to-point '(:character 60 :line 2)) 73))))
+
 (provide 'eglot-tests)
 ;;; eglot-tests.el ends here
 

eglot.el

@@ -700,16 +700,30 @@ CONNECT-ARGS are passed as additional arguments to
          :character (- (goto-char (or pos (point)))
                        (line-beginning-position)))))
 
+(defun eglot--lsp-char-to-column (lsp-charpos)
+  "Helper for `eglot--lsp-position-to-point'."
+  (let ((line (buffer-substring-no-properties (point) (line-end-position))))
+    (with-temp-buffer
+      (save-excursion (insert line))
+      (cl-loop with start-filepos =
+               (bufferpos-to-filepos (point) 'exact 'utf-16-unix)
+               for current-pos = start-filepos
+               then (bufferpos-to-filepos (point) 'exact 'utf-16-unix)
+               while (and (not (eolp))
+                          (< (/ (- current-pos start-filepos) 2)
+                             lsp-charpos))
+               do (forward-char)
+               finally do (cl-return (1- (point)))))))
+
 (defun eglot--lsp-position-to-point (pos-plist &optional marker)
   "Convert LSP position POS-PLIST to Emacs point.
 If optional MARKER, return a marker instead"
-  (save-excursion (goto-char (point-min))
-                  (forward-line (min most-positive-fixnum
-                                     (plist-get pos-plist :line)))
-                  (forward-char (min (plist-get pos-plist :character)
-                                     (- (line-end-position)
-                                        (line-beginning-position))))
-                  (if marker (copy-marker (point-marker)) (point))))
+  (save-excursion
+    (goto-char (point-min))
+    (forward-line (min most-positive-fixnum
+                       (plist-get pos-plist :line)))
+    (forward-char (eglot--lsp-char-to-column (plist-get pos-plist :character)))
+    (if marker (copy-marker (point-marker)) (point))))
 
 (defun eglot--path-to-uri (path)
   "URIfy PATH."
@@ -1943,63 +1957,53 @@ If SKIP-SIGNATURE, don't try to send textDocument/signatureHelp."
 
 (defun eglot--eclipse-jdt-contact (interactive)
   "Return a contact for connecting to eclipse.jdt.ls server, as a cons cell."
-  (cl-labels
-      ((is-the-jar
-        (path)
-        (and (string-match-p
-              "org\\.eclipse\\.equinox\\.launcher_.*\\.jar$"
-              (file-name-nondirectory path))
-             (file-exists-p path))))
-    (let* ((classpath (or (getenv "CLASSPATH") ":"))
-           (cp-jar (cl-find-if #'is-the-jar (split-string classpath ":")))
-           (jar cp-jar)
-           (dir
-            (cond
-             (jar (file-name-as-directory
-                   (expand-file-name ".." (file-name-directory jar))))
-             (interactive
-              (expand-file-name
-               (read-directory-name
-                (concat "Path to eclipse.jdt.ls directory (could not"
-                        " find it in CLASSPATH): ")
-                nil nil t)))
-             (t (error "Could not find eclipse.jdt.ls jar in CLASSPATH"))))
-           (repodir
-            (concat dir
-                    "org.eclipse.jdt.ls.product/target/repository/"))
-           (repodir (if (file-directory-p repodir) repodir dir))
-           (config
-            (concat
-             repodir
-             (cond
-              ((string= system-type "darwin") "config_mac")
-              ((string= system-type "windows-nt") "config_win")
-              (t "config_linux"))))
-           (project (or (project-current) `(transient . ,default-directory)))
-           (workspace
-            (expand-file-name (md5 (car (project-roots project)))
-                              (concat user-emacs-directory
-                                      "eglot-eclipse-jdt-cache"))))
-      (unless jar
-        (setq jar
-              (cl-find-if #'is-the-jar
-                          (directory-files (concat repodir "plugins") t))))
-      (unless (and jar (file-exists-p jar) (file-directory-p config))
-        (error "Could not find required eclipse.jdt.ls files (build required?)"))
-      (when (and interactive (not cp-jar)
-                 (y-or-n-p (concat "Add path to the server program "
-                                   "to CLASSPATH environment variable?")))
-        (setenv "CLASSPATH" (concat (getenv "CLASSPATH") ":" jar)))
-      (unless (file-directory-p workspace)
-        (make-directory workspace t))
-      (cons 'eglot-eclipse-jdt
-            (list (executable-find "java")
-                  "-Declipse.application=org.eclipse.jdt.ls.core.id1"
-                  "-Dosgi.bundles.defaultStartLevel=4"
-                  "-Declipse.product=org.eclipse.jdt.ls.core.product"
-                  "-jar" jar
-                  "-configuration" config
-                  "-data" workspace)))))
+
+
+  (if-let ((jar (cl-find "org\\.eclipse\\.equinox\\.launcher_.*\\.jar$"
+                         (split-string (getenv "CLASSPATH") ":")
+                         :test #'string-match-p
+                         :key #'file-name-nondirectory)))
+      (setq dir (expand-file-name "../" (file-name-directory jar)))
+
+    )
+
+  (let (config
+        (jar
+         (or 
+          (interactive
+           (setq dir (read-directory-name
+                      (concat "Path to eclipse.jdt.ls directory (could not"
+                              " find it in CLASSPATH): ")
+                      nil nil t))
+           (setq repodir
+                 (find #'file-directory-p
+                       (expand-file-name "org.eclipse.jdt.ls.product/target/repository/" dir)
+                       dir))
+           (setq config
+                 (expand-file-name
+                  (cond
+                   ((string= system-type "darwin") "config_mac")
+                   ((string= system-type "windows-nt") "config_win")
+                   (t "config_linux"))
+                  repodir)))))
+
+
+        (unless (and jar (file-exists-p jar) (file-directory-p config))
+          (error "Could not find required eclipse.jdt.ls files (build required?)"))
+        (when (and interactive (not cp-jar)
+                   (y-or-n-p (concat "Add path to the server program "
+                                     "to CLASSPATH environment variable?")))
+          (setenv "CLASSPATH" (concat (getenv "CLASSPATH") ":" jar)))
+        (unless (file-directory-p workspace)
+          (make-directory workspace t))
+        (cons 'eglot-eclipse-jdt
+              (list (executable-find "java")
+                    "-Declipse.application=org.eclipse.jdt.ls.core.id1"
+                    "-Dosgi.bundles.defaultStartLevel=4"
+                    "-Declipse.product=org.eclipse.jdt.ls.core.product"
+                    "-jar" jar
+                    "-configuration" config
+                    "-data" workspace)))))
 
 (cl-defmethod eglot-execute-command
   ((_server eglot-eclipse-jdt) (_cmd (eql java.apply.workspaceEdit)) arguments)