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Add ability to report lsp-compliant columns
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* eglot.el (eglot-current-column-function): New variable.
(eglot-lsp-abiding-column): New helper.
(eglot--pos-to-lsp-position): Use eglot-current-column-function.
(eglot-move-to-column-function): Tweak docstring.

GitHub-reference: fix joaotavora/eglot#125
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joaotavora committed Nov 13, 2018
1 parent 5c97238 commit 8df3bdd
Showing 1 changed file with 24 additions and 8 deletions.
32 changes: 24 additions & 8 deletions lisp/progmodes/eglot.el
Original file line number Diff line number Diff line change
Expand Up @@ -721,26 +721,42 @@ CONNECT-ARGS are passed as additional arguments to
(let ((warning-minimum-level :error))
(display-warning 'eglot (apply #'format format args) :warning)))

(defvar eglot-current-column-function #'current-column
"Function to calculate the current column.
This is the inverse operation of
`eglot-move-to-column-function' (which see). It is a function of
no arguments returning a column number. For buffers managed by
fully LSP-compliant servers, this should be set to
`eglot-lsp-abiding-column', and `current-column' (the default)
for all others.")

(defun eglot-lsp-abiding-column ()
"Calculate current COLUMN as defined by the LSP spec."
(/ (- (length (encode-coding-region (line-beginning-position)
(point) 'utf-16 t))
2)
2))

(defun eglot--pos-to-lsp-position (&optional pos)
"Convert point POS to LSP position."
(eglot--widening
(list :line (1- (line-number-at-pos pos t)) ; F!@&#$CKING OFF-BY-ONE
:character (- (goto-char (or pos (point)))
(line-beginning-position)))))
:character (progn (when pos (goto-char pos))
(funcall eglot-current-column-function)))))

(defvar eglot-move-to-column-function #'move-to-column
"How to move to a column reported by the LSP server.
"Function to move to a column reported by the LSP server.
According to the standard, LSP column/character offsets are based
on a count of UTF-16 code units, not actual visual columns. So
when LSP says position 3 of a line containing just \"aXbc\",
where X is a multi-byte character, it actually means `b', not
`c'. This is what the function
`eglot-move-to-lsp-abiding-column' does.
`c'. However, many servers don't follow the spec this closely.
However, many servers don't follow the spec this closely, and
thus this variable should be set to `move-to-column' in buffers
managed by those servers.")
For buffers managed by fully LSP-compliant servers, this should
be set to `eglot-move-to-lsp-abiding-column', and
`move-to-column' (the default) for all others.")

(defun eglot-move-to-lsp-abiding-column (column)
"Move to COLUMN abiding by the LSP spec."
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