EMACS NS VOICEOVER ACCESSIBILITY PATCH
========================================
patch: 0001-0008 (8 patches, see PATCH SERIES below)
author: Martin Sukany <martin@sukany.cz>
files: src/nsterm.h (+124 lines)
src/nsterm.m (+3577 ins, -185 del, +3392 net)
doc/emacs/macos.texi (+53 lines)
etc/NEWS (+13 lines)
PATCH SERIES
------------
0001 ns: add accessibility base classes and text extraction
0002 ns: implement buffer accessibility element (core protocol)
0003 ns: add buffer notification dispatch and mode-line element
0004 ns: add interactive span elements for Tab navigation
0005 ns: integrate accessibility with EmacsView and redisplay
0006 doc: add VoiceOver accessibility section to macOS appendix
0007 ns: announce overlay completion candidates for VoiceOver
0008 ns: announce child frame completion candidates for VoiceOver
0009 Performance: precomputed line index for O(log L) line queries
OVERVIEW
--------
This patch adds comprehensive macOS VoiceOver accessibility support
to the Emacs NS (Cocoa) port. Before this patch, Emacs exposed only
a minimal, largely broken accessibility interface to macOS assistive
technology (AT) clients: EmacsView identified itself as a generic
NSAccessibilityGroup with no text content, no cursor tracking, and
no notifications. VoiceOver users could activate the application
but received no meaningful speech feedback when editing text.
The patch introduces a layered virtual element tree above EmacsView.
Each visible Emacs window is represented by an EmacsAccessibilityBuffer
element (AXTextArea / AXTextField for minibuffer) with a full text
cache, a visible-run mapping table that bridges buffer character
positions to UTF-16 accessibility string indices, and an interactive
span child array for Tab navigation. A companion
EmacsAccessibilityModeLine element (AXStaticText) represents the mode
line of each window. These virtual elements are wired into the macOS
Accessibility API through EmacsView acting as the AXGroup root.
Two additional integration points are provided: (1) macOS Zoom is
informed of the cursor position after every physical cursor redraw via
UAZoomChangeFocus(), using the correct CoreGraphics (top-left-origin)
coordinate space; (2) EmacsView implements accessibilityBoundsForRange:
and its legacy parameterized-attribute equivalent so that both Zoom
and third-party AT tools can locate the insertion point. The patch
also covers completion announcements for the *Completions* buffer and
Tab-navigable interactive spans for buttons, links, checkboxes,
Org-mode links, completion candidates, and keymap overlays.
ARCHITECTURE
------------
Class hierarchy (Cocoa only):
NSAccessibilityElement
|
+-- EmacsAccessibilityElement (base: owns emacsView + lispWindow)
|
+-- EmacsAccessibilityBuffer (AXTextArea; one per leaf window)
| [category InteractiveSpans] (Tab nav children)
|
+-- EmacsAccessibilityModeLine (AXStaticText; one per non-mini)
|
+-- EmacsAccessibilityInteractiveSpan (AXButton/Link/etc.)
EmacsView (NSView subclass, existing)
|
+-- owns NSMutableArray *accessibilityElements
contains EmacsAccessibilityBuffer + EmacsAccessibilityModeLine
instances for every visible leaf window and minibuffer.
EmacsAccessibilityInteractiveSpan instances are children of
their parent EmacsAccessibilityBuffer, NOT of this array.
EmacsAccessibilityElement (base class)
- Stores a weak (unsafe_unretained) pointer to EmacsView and a
Lisp_Object lispWindow (GC-safe window reference).
- Provides -validWindow which verifies WINDOW_LIVE_P before
returning the raw struct window *. All subclasses use this to
avoid dangling pointers after delete-window or kill-buffer.
- Provides -screenRectFromEmacsX:y:width:height: which converts
EmacsView pixel coordinates (flipped AppKit space) to screen
coordinates via the NSWindow coordinate chain.
EmacsAccessibilityBuffer
- Implements the full NSAccessibility text protocol: value, selected
text range, line/index/range conversions, frame-for-range,
range-for-position, and insertion-point-line-number.
- Maintains a text cache (cachedText / visibleRuns) keyed on
BUF_MODIFF and BUF_BEGV (narrowing). BUF_OVERLAY_MODIFF is
tracked separately for notification dispatch (patch 0007)
but not for cache invalidation.
The cache is the single source of truth for all
index-to-charpos and charpos-to-index mappings.
- Detects buffer edits (modiff change), cursor movement (point
change), and mark changes, and posts the appropriate
NSAccessibility notifications after each redisplay cycle.
- Stores cached values for the previous cycle (cachedModiff,
cachedPoint, cachedMarkActive) to enable change detection.
EmacsAccessibilityModeLine
- Reads mode line text directly from the window's current glyph
matrix (CHAR_GLYPH rows with mode_line_p set).
- Stateless: no cache; text is read fresh on every AX query.
EmacsAccessibilityInteractiveSpan
- Lightweight child element representing one contiguous interactive
region (button, link, completion item, etc.).
- Reports isAccessibilityFocused by comparing cachedPoint of the
parent EmacsAccessibilityBuffer against its charpos range.
- On setAccessibilityFocused: dispatches to the main queue via
GCD to move Emacs point, using block_input around SET_PT_BOTH.
EmacsView (extensions)
- accessibilityElements array: rebuilt by -rebuildAccessibilityTree
when the window tree changes (split, delete, new buffer).
- -postAccessibilityUpdates: called from ns_update_end() after
every redisplay cycle; drives the notification dispatch loop.
- lastAccessibilityCursorRect: updated by ns_draw_phys_cursor
(C function) for Zoom integration.
- Implements accessibilityBoundsForRange: /
accessibilityFrameForRange: and the legacy
accessibilityAttributeValue:forParameter: API.
USER OPTION
-----------
ns-accessibility-enabled (DEFVAR_BOOL, default t):
When nil, the accessibility virtual element tree is not built, no
notifications are posted, and ns_draw_phys_cursor skips the Zoom
update. This eliminates accessibility overhead entirely on systems
where assistive technology is not in use. Guarded at three entry
points: postAccessibilityUpdates, ns_draw_phys_cursor, and
windowDidBecomeKey.
THREADING MODEL
---------------
Emacs runs all Lisp evaluation and buffer mutation on the main thread
(the Cocoa/AppKit main thread). The macOS Accessibility server
(axserver / AT daemon) calls AX getters from a private background
thread.
Rules enforced by this patch:
Main thread only:
- ns_update_end -> postAccessibilityUpdates
- rebuildAccessibilityTree / invalidateAccessibilityTree
- ensureTextCache / ns_ax_buffer_text (Lisp calls:
Fget_char_property, Fnext_single_char_property_change,
Fbuffer_substring_no_properties)
- postAccessibilityNotificationsForFrame: (full notify logic)
- setAccessibilitySelectedTextRange: (SET_PT_BOTH, marker moves)
- setAccessibilityFocused: on EmacsAccessibilityInteractiveSpan
(dispatches to main queue via dispatch_async; uses specpdl
unwind protection so block_input is always matched by
unblock_input even if Fselect_window signals an error)
- ns_draw_phys_cursor partial update (lastAccessibilityCursorRect,
UAZoomChangeFocus)
Safe from any thread (no Lisp calls, no mutable Emacs state):
- accessibilityIndexForCharpos: reads visibleRuns + cachedText
- charposForAccessibilityIndex: same
- isAccessibilityFocused on EmacsAccessibilityInteractiveSpan
(reads cachedPoint, a plain ptrdiff_t)
Dispatch-gated (marshalled to main thread when called off-thread):
- accessibilityValue (EmacsAccessibilityBuffer)
- accessibilitySelectedTextRange
- accessibilityInsertionPointLineNumber
- accessibilityFrameForRange:
- accessibilityRangeForPosition:
- accessibilityChildrenInNavigationOrder
The marshalling pattern used throughout:
if (![NSThread isMainThread]) {
__block T result;
dispatch_sync(dispatch_get_main_queue(), ^{ result = ...; });
return result;
}
Async notification posting (deadlock prevention):
NSAccessibilityPostNotification may synchronously invoke VoiceOver
callbacks from a private AX server thread. Those callbacks call
AX getters which dispatch_sync back to the main queue. If the
main thread is still inside the notification-posting method (e.g.,
postAccessibilityUpdates called from ns_update_end), the
dispatch_sync deadlocks: the main thread waits for VoiceOver to
finish processing the notification, while VoiceOver's thread waits
for the main queue to become available.
To break this cycle, all notification posting goes through two
static inline wrappers:
ns_ax_post_notification(element, name)
ns_ax_post_notification_with_info(element, name, info)
These wrappers defer the actual NSAccessibilityPostNotification
call via dispatch_async(dispatch_get_main_queue(), ^{ ... }).
The current method returns first, freeing the main queue, so
VoiceOver's dispatch_sync calls can proceed without deadlock.
Block captures retain ObjC objects (element, info dictionary)
for the lifetime of the deferred block.
Cached data written on main thread and read from any thread:
- cachedText (NSString *): written by ensureTextCache on main.
- visibleRuns (ns_ax_visible_run *): written by ensureTextCache.
- cachedPoint (ptrdiff_t): plain scalar; atomic on 64-bit ARM/x86.
No explicit lock is used; the design relies on the fact that index
mapping methods make no Lisp calls and read only the above scalars
and the immutable NSString object.
NOTIFICATION STRATEGY
---------------------
All notifications are posted asynchronously via
ns_ax_post_notification / ns_ax_post_notification_with_info
(dispatch_async wrappers -- see THREADING MODEL for rationale).
Notifications are generated by -postAccessibilityNotificationsForFrame:
which runs on the main thread after every redisplay cycle. The
method detects three mutually exclusive events:
1. TEXT CHANGED (modiff != cachedModiff)
Posts NSAccessibilityValueChangedNotification with AXTextEditType
= Typing and, when exactly one character was inserted, provides
AXTextChangeValue for echo feedback. cachedPoint is updated here
to suppress a spurious selection-move event in the same cycle
(WebKit/Chromium convention: edit and selection-move are mutually
exclusive per runloop iteration).
2. CURSOR MOVED OR MARK CHANGED (point != cachedPoint OR mark change)
Granularity is computed by comparing oldIdx and newIdx in
cachedText:
- different line range -> LINE granularity
- same line, distance > 1 UTF-16 unit -> WORD granularity
- same line, distance == 1 UTF-16 unit -> CHARACTER granularity
C-n / C-p / Tab / backtab force LINE granularity
(detected by ns_ax_event_is_line_nav_key which inspects
last_command_event) regardless.
For FOCUSED elements the hybrid strategy applies:
CHARACTER moves:
SelectedTextChanged is posted WITHOUT AXTextSelectionGranularity
in userInfo. Omitting the key prevents VoiceOver from deriving
its own speech (it would read the character BEFORE point,
which is wrong for evil block-cursor mode where the cursor
sits ON the character). Then AnnouncementRequested is posted
separately with the character AT point as the announcement.
Newline is skipped (VoiceOver handles end-of-line internally).
WORD and LINE moves:
SelectedTextChanged is posted WITH AXTextSelectionGranularity.
VoiceOver reads the word/line correctly from the element text
using the granularity hint. For LINE moves an additional
AnnouncementRequested is also posted with the line text (or
the completion--string at point if in a completion buffer) to
handle C-n/C-p -- VoiceOver processes these keystrokes
differently from arrow keys internally.
SELECTION changes (mark becomes active or extends):
SelectedTextChanged with LINE or WORD granularity. VoiceOver
reads the newly selected or deselected text.
For NON-FOCUSED elements (e.g. *Completions* while minibuffer has
focus): AnnouncementRequested only. See COMPLETION ANNOUNCEMENTS.
3. NO CHANGE
Nothing is posted. Completion cache is cleared for focused buffer.
TEXT CACHE AND VISIBLE RUNS
----------------------------
ns_ax_buffer_text(w, out_start, out_runs, out_nruns) builds the
accessibility string for window W. It operates on the current
buffer with set_buffer_internal_1, scanning from BUF_BEGV to BUF_ZV.
Invisible text detection uses TEXT_PROP_MEANS_INVISIBLE(invis) where
invis = Fget_char_property(pos, Qinvisible, Qnil). This respects
buffer-invisibility-spec, correctly handling org-mode folding,
outline mode, and hideshow -- not just `invisible t' text properties.
When an invisible region is found, the scanner jumps ahead using
Fnext_single_char_property_change to skip the entire region in O(1)
iterations rather than character by character.
Text extraction uses Fbuffer_substring_no_properties (not raw
BUF_BYTE_ADDRESS) to handle the buffer gap correctly. Raw byte
access across the gap position yields garbage bytes.
The ns_ax_visible_run structure:
typedef struct ns_ax_visible_run {
ptrdiff_t charpos; /* Buffer charpos of run start. */
ptrdiff_t length; /* Emacs characters in this run. */
NSUInteger ax_start; /* UTF-16 index in accessibility string. */
NSUInteger ax_length; /* UTF-16 units for this run. */
} ns_ax_visible_run;
Multiple runs are produced when invisible text splits the buffer into
non-contiguous visible segments. The mapping array is stored in the
EmacsAccessibilityBuffer ivar `visibleRuns' (C array, xmalloc'd).
Index mapping (charpos <-> ax_index) uses binary search over the
sorted run array — O(log n) per lookup. Within a run, UTF-16 unit
counting uses
rangeOfComposedCharacterSequenceAtIndex: to handle surrogate pairs
(emoji, rare CJK) correctly -- one Emacs character may occupy 2
UTF-16 units.
Cache invalidation is triggered whenever BUF_MODIFF or
BUF_OVERLAY_MODIFF changes (ensureTextCache compares both
cachedTextModiff and cachedOverlayModiff). Additionally,
narrowing/widening is detected by comparing cachedTextStart
against BUF_BEGV — these operations change the visible region
without bumping either modiff counter. The cache is also
invalidated when the window tree is rebuilt.
There is no character cap on the accessibility text. The entire
visible (non-invisible) buffer content is exposed to VoiceOver.
Users who do not need accessibility can set ns-accessibility-enabled
to nil for zero overhead.
A lineStartOffsets array is built during each cache rebuild,
recording the AX string index where each line begins. This
makes accessibilityLineForIndex: and accessibilityRangeForLine:
O(log L) via binary search instead of O(L) linear scanning.
The index is freed and rebuilt alongside the text cache.
COMPLETION ANNOUNCEMENTS
------------------------
When point moves in a non-focused buffer (the common case:
*Completions* window while the minibuffer retains keyboard focus),
VoiceOver does not automatically read the change because it is
tracking the focused element. The patch posts AnnouncementRequested
with a 4-step fallback chain to find the best text to announce:
Step 1 -- completion--string property at point.
The `completion--string' text property (set by minibuffer.el
since Emacs 29) carries the canonical completion candidate string.
It can be a plain Lisp string or a list (CANDIDATE ANNOTATION) where both
are strings.
ns_ax_completion_string_from_prop handles both: plain string ->
use directly; cons -> use car (the candidate without annotation).
This is the preferred source: precisely the candidate text with
no surrounding whitespace.
Step 2 -- mouse-face span at point.
completion-list-mode marks the active candidate with mouse-face.
The code walks backward and forward from point to find the span
boundaries, then reads the corresponding slice of cachedText.
Used when completion--string is absent (older Emacs or non-
standard completion modes).
Step 3 -- completions-highlight overlay at point.
Emacs 29+ highlights the selected completion with the
`completions-highlight' face applied via an overlay. The overlay
text is extracted via ns_ax_completion_text_for_span which itself
tries completion--string first, then the `completion' property,
then falls back to the ax string slice.
Step 4 -- nearest completions-highlight overlay.
ns_ax_find_completion_overlay_range scans the buffer for the
closest completions-highlight overlay to point. Uses fast probes
at {point, point+1, point-1} before falling back to a full O(n)
scan.
Final fallback -- current line text.
Read the line containing point from cachedText.
Deduplication: the announcement is posted only when announceText,
overlay bounds, or point have changed since the last cycle
(cachedCompletionAnnouncement, cachedCompletionOverlayStart/End,
cachedCompletionPoint).
INTERACTIVE SPANS
-----------------
ns_ax_scan_interactive_spans(w, parent_buf) scans the visible range
of window W looking for text properties that indicate interactive
content. Properties are checked in priority order:
widget -> EmacsAXSpanTypeWidget (AXButton, via default)
button -> EmacsAXSpanTypeButton (AXButton, via default)
follow-link -> EmacsAXSpanTypeLink (AXLink)
org-link -> EmacsAXSpanTypeLink (AXLink)
mouse-face -> EmacsAXSpanTypeCompletionItem
(AXButton; completion-list-mode only)
keymap overlay-> EmacsAXSpanTypeButton (AXButton)
For completion buffers (major-mode == completion-list-mode), the span
boundary for mouse-face regions uses completion--string as the property
key when present, rather than mouse-face itself. This prevents two
column-adjacent completion candidates from being merged into one span
when their mouse-face regions share padding whitespace.
All property symbols are registered with DEFSYM in syms_of_nsterm
using ns_ax_ prefixed C variable names (e.g., Qns_ax_button for
"button") to avoid collisions with other Emacs source files.
Referenced directly -- no repeated intern() calls.
Each span is allocated, configured, added to the spans array, then
released (the array retains it). The function returns an autoreleased
immutable copy of the spans array. Label priority:
completion--string > buffer substring > help-echo.
Tab navigation: -accessibilityChildrenInNavigationOrder returns the
cached span array, rebuilt lazily when interactiveSpansDirty is set.
Calls from off-thread are marshalled with dispatch_sync.
Focus movement: -setAccessibilityFocused: on a span dispatches
Fselect_window + SET_PT_BOTH to the main queue via dispatch_async,
wrapped in block_input/unblock_input.
ZOOM INTEGRATION
----------------
macOS Zoom (accessibility zoom) tracks a "focus element" to keep the
zoomed viewport centered on the relevant screen area. Two mechanisms
are provided:
1. ns_draw_phys_cursor (C function, main thread, called during
redisplay). After clipping the cursor rect to the text area,
stores the rect in view->lastAccessibilityCursorRect. If
UAZoomEnabled(), converts the rect to screen coordinates and calls
UAZoomChangeFocus(kUAZoomFocusTypeInsertionPoint).
Coordinate conversion chain:
EmacsView pixels (AppKit, flipped, origin at top-left of view)
-[convertRect:toView:nil]-> NSWindow coordinates
-[convertRectToScreen:]-> NSScreen coordinates
NSRectToCGRect -> CGRect (same values, no transform)
CG y-flip: cgRect.origin.y = primaryH - y - height
The flip is required because CoreGraphics uses top-left origin
(primary screen) while AppKit screen rects use bottom-left.
primaryH = [[NSScreen screens] firstObject].frame.size.height.
2. EmacsView -accessibilityBoundsForRange: /
-accessibilityFrameForRange:
AT tools (including Zoom) call these with the selectedTextRange
to locate the insertion point. The implementation first delegates
to the focused EmacsAccessibilityBuffer element for accurate
per-range geometry via its accessibilityFrameForRange: method.
If the buffer element returns an empty rect (no valid window or
glyph data), the fallback uses the cached cursor rect stored in
lastAccessibilityCursorRect (minimum size 1x8 pixels). The legacy
parameterized-attribute API
(NSAccessibilityBoundsForRangeParameterizedAttribute) is supported
via -accessibilityAttributeValue:forParameter: for older AT
clients.
KEY DESIGN DECISIONS
--------------------
1. DEFSYM instead of intern for all frequently-used symbols.
DEFSYM registers symbols at startup (syms_of_nsterm) and stores
them in C globals (e.g. Qns_ax_completion__string, Qns_ax_next_line).
This covers both property scanning symbols and line navigation
command symbols used in ns_ax_event_is_line_nav_key (hot path:
runs on every cursor movement). Using intern() would perform
obarray lookups on each redisplay cycle. DEFSYM symbols are
also always reachable by the GC via staticpro, eliminating any
risk of premature collection.
2. AnnouncementRequested for character moves, not SelectedTextChanged.
VoiceOver derives the speech character from SelectedTextChanged by
looking at the character BEFORE the new cursor position (the char
"passed over"). In evil-mode with a block cursor, the cursor sits
ON the character, not between characters. AnnouncementRequested
with the character AT point produces correct speech in both insert
and normal (block-cursor) modes. SelectedTextChanged is still
posted without granularity to interrupt ongoing VoiceOver reading
and update braille display tracking.
3. completion--string, not mouse-face, as span boundary.
mouse-face regions in completion-list-mode sometimes include
leading or trailing whitespace shared between column-adjacent
candidates, which could merge two candidates into one span.
completion--string changes precisely at candidate boundaries.
4. Probe order {point, point+1, point-1} for overlay search.
After Tab advances to a new completion candidate, point is at the
START of the new entry. The previous entry's overlay covers the
position before the new start, so point-1 is inside the OLD
overlay. Trying point+1 before point-1 finds the new (correct)
entry first.
5. Notifications posted BEFORE rebuilding the tree.
postAccessibilityUpdates uses existing elements which carry cached
state from the previous cycle. Rebuilding first would create
fresh elements with current values, making change detection
impossible. Tree rebuild is deferred to cycles where
accessibilityTreeValid is false; no notifications are posted in
that cycle.
6. Re-entrance guard (accessibilityUpdating flag).
VoiceOver callbacks triggered by notification posting can cause
Cocoa to re-enter the run loop, which may trigger redisplay, which
calls ns_update_end -> postAccessibilityUpdates. The BOOL flag
breaks this recursion.
6a. Async notification posting (dispatch_async wrappers).
NSAccessibilityPostNotification can synchronously trigger
VoiceOver queries from a background AX server thread. Those
queries dispatch_sync to the main queue. If the main thread
is still inside postAccessibilityUpdates (or windowDidBecomeKey,
or setAccessibilityFocused:), the dispatch_sync deadlocks.
All 14 notification sites use ns_ax_post_notification / _with_info
wrappers that defer posting via dispatch_async, freeing the main
queue before VoiceOver's callbacks arrive. This follows the same
pattern used by WebKit's AXObjectCacheMac (deferred posting via
performSelector:withObject:afterDelay:0).
7. lispWindow (Lisp_Object) instead of raw struct window *.
struct window pointers can become dangling after delete-window.
Storing the Lisp_Object and using WINDOW_LIVE_P + XWINDOW at the
call site is the standard safe pattern in Emacs C code.
8. accessibilityVisibleCharacterRange returns full buffer range.
VoiceOver treats the visible range boundary as end-of-text. If
this returned only the on-screen portion, VoiceOver would announce
"end of text" prematurely when the cursor reaches the visible
bottom, even though more buffer content exists below.
OVERLAY COMPLETION ANNOUNCEMENTS (Patch 0007)
----------------------------------------------
Overlay-based completion frameworks (Vertico, Icomplete, Ivy, etc.)
render candidates as overlay strings in the minibuffer. VoiceOver
does not see overlay content changes automatically. This patch
detects overlay candidate changes and announces the selected
candidate.
Detection:
ns_ax_face_is_selected(face) checks whether a face name contains
"current", "selected", or "selection" (matching vertico-current,
icomplete-selected-match, ivy-current-match, etc.). Supports
both single face symbols and face lists.
ns_ax_selected_overlay_text(b, beg, end, out_line) scans the
buffer region line by line using Fget_char_property to check
both text properties and overlay face properties.
Overlay changes are tracked independently of text changes:
BUF_OVERLAY_MODIFF is checked in an independent if-branch (not
else-if) because Vertico bumps both BUF_MODIFF (text properties)
and BUF_OVERLAY_MODIFF (overlays) in the same command cycle.
textDidChange flag:
hl-line-mode and similar packages update face properties (text
properties, not characters) on every cursor movement, bumping
BUF_MODIFF without changing BUF_CHARS_MODIFF. The original
else-if structure caused the modiff branch to fire (correctly
skipping ValueChanged) but also blocked the cursor-move branch
(SelectedTextChanged). A BOOL textDidChange flag decouples the
two branches: ValueChanged and SelectedTextChanged remain
mutually exclusive for real edits, but SelectedTextChanged fires
correctly when only text properties changed.
Zoom:
The selected candidate position is stored in overlayZoomRect /
overlayZoomActive on the parent EmacsView. draw_window_cursor
uses this rect instead of the text cursor when a candidate is
active. Cleared when BUF_CHARS_MODIFF changes (user types)
or when no candidate is found.
CHILD FRAME COMPLETION ANNOUNCEMENTS (Patch 0008)
--------------------------------------------------
Completion frameworks such as Corfu, Company-box, and similar render
candidates in a child frame rather than as overlay strings. This
patch detects child frames via FRAME_PARENT_FRAME and announces
the selected candidate.
Detection:
Child frames are dispatched in postAccessibilityUpdates before
the main tree rebuild logic. FRAME_PARENT_FRAME(emacsframe)
returns non-NULL for child frames.
ns_ax_selected_child_frame_text(b, buf_obj, out_line) scans the
child frame buffer line by line, reusing ns_ax_face_is_selected
from patch 0007.
Buffer switch safety:
Fbuffer_substring_no_properties operates on current_buffer, which
may differ from the child frame buffer during ns_update_end.
The function uses record_unwind_current_buffer /
set_buffer_internal_1 to temporarily switch, with unbind_to on
all three return paths after the switch. Uses specpdl_ref (not
ptrdiff_t) for the SPECPDL_INDEX return value.
Re-entrance protection:
The accessibilityUpdating guard MUST precede the child frame
dispatch because Lisp calls in the scan function (Fget_char_property,
Fbuffer_substring_no_properties) can trigger redisplay.
BUF_MODIFF gating provides a secondary guard and prevents
redundant scans.
Validation:
- WINDOWP / BUFFERP checks for partially initialized child frames.
- Buffer size limit (10000 chars) skips non-completion child frames
(eldoc, which-key, etc.).
Focus restoration:
childFrameCompletionActive (BOOL on EmacsView) is set by the child
frame handler on the parent view. On the parent's next accessibility
cycle, FOR_EACH_FRAME checks whether any child frame is still
visible. If not, FocusedUIElementChangedNotification is posted on
the focused buffer element to restore VoiceOver character echo and
cursor tracking.
Zoom:
Direct UAZoomChangeFocus (not overlayZoomRect) because the child
frame's ns_update_end runs after the parent's draw_window_cursor,
so the last Zoom call wins.
Deduplication:
Static C string cache (lastCandidate via xstrdup/xfree) avoids
re-announcing the same candidate.
KNOWN LIMITATIONS
-----------------
- Interactive span scan uses Fnext_single_property_change across
multiple properties to skip non-interactive regions in bulk, but
still visits every property-change boundary. For buffers with
many overlapping text properties (e.g. heavily fontified source
code), the number of boundaries can be significant. The scan
runs on every redisplay cycle when interactiveSpansDirty is set.
- Mode line text is extracted from CHAR_GLYPH rows only. Image
glyphs, stretch glyphs, and composed glyphs are silently skipped.
Mode lines with icon fonts (e.g. doom-modeline with nerd-font)
produce incomplete or garbled accessibility text.
- Line counting (accessibilityInsertionPointLineNumber,
accessibilityLineForIndex:) uses a precomputed lineStartOffsets
array built once per cache rebuild. Queries are O(log L) via
binary search.
- No multi-frame coordination. EmacsView.accessibilityElements is
per-view; there is no cross-frame notification ordering.
- Overlay completion (0007) face matching uses string containment
("current", "selected", "selection"). Custom completion frameworks
with face names not containing these substrings will not be detected.
- Child frame completion (0008) static lastBuffer pointer may become
stale if the buffer is freed and a new one allocated at the same
address. This is harmless (worst case: one missed announcement).
- Child frame window-appeared announcement: macOS automatically
announces the window title when a child frame NSWindow appears.
This cannot be suppressed without breaking VoiceOver focus tracking
or Zoom integration.
- GNUstep is explicitly excluded (#ifdef NS_IMPL_COCOA). GNUstep
has a different accessibility model and requires separate work.
- Line navigation detection (ns_ax_event_is_line_nav_key) checks
Vthis_command against known navigation command symbols
(next-line, previous-line, evil-next-line, etc.) and falls back
to raw key codes for Tab/backtab. Custom navigation commands
not in the recognized list will not get forced line-granularity
announcements.
- UAZoomChangeFocus always uses kUAZoomFocusTypeInsertionPoint
regardless of cursor style (box, bar, hbar). This is cosmetically
imprecise but functionally correct.
TESTING CHECKLIST
-----------------
Prerequisites:
- macOS with VoiceOver (Cmd-F5 to toggle).
- Emacs built from source with this patch applied.
- Evil-mode recommended for block-cursor tests.
Basic text reading:
1. Open Emacs. Press Cmd-F5 to start VoiceOver.
2. Switch to Emacs (Cmd-Tab). VoiceOver should announce
"Emacs, editor" and read the current line.
3. Move cursor with arrow keys. VoiceOver should read each
character (left/right) or line (up/down) as you move.
4. Verify: right/left arrow reads the character AT the cursor
position, not the character left behind. (evil block-cursor)
Word and line navigation:
5. Press M-f / M-b (forward/backward word). VoiceOver should
announce the word landed on.
6. Press C-n / C-p. VoiceOver should read the full new line.
7. Hold Shift and press arrow keys to extend selection. VoiceOver
should announce the selected text.
Completion navigation:
8. Type M-x to open the minibuffer.
9. Type a partial command name. Press Tab to open *Completions*.
10. Press Tab / S-Tab to cycle through completions. VoiceOver
should announce each candidate name as you move.
11. Verify no double-speech (each candidate read exactly once).
Interactive span Tab navigation:
12. Open a buffer with buttons (e.g. M-x describe-key).
13. Use VoiceOver Item Chooser (VO-I) or Tab with VoiceOver
interaction mode to navigate interactive elements.
14. Verify each button/link is reachable and its label is read.
15. In an org-mode file with links, verify links appear as
separate navigable AXLink elements.
Mode line:
16. Use the VoiceOver cursor to navigate to the mode line below a
buffer. VoiceOver should read the mode line text.
Zoom integration:
17. Enable macOS Zoom (System Settings -> Accessibility -> Zoom).
18. Set Zoom to "Follow keyboard focus".
19. Move cursor in Emacs. Zoom viewport should track the cursor.
20. Verify Zoom follows the cursor across split windows.
Window operations:
21. Split window with C-x 2. VoiceOver should announce a layout
change. Switch with C-x o; VoiceOver should read the new
window content.
22. Delete a window with C-x 0. No crash should occur.
23. Switch buffers with C-x b. VoiceOver should read new buffer.
Deadlock regression (async notifications):
24. With VoiceOver on: M-x, type partial command, M-v to
*Completions*, Tab to a candidate, Enter to execute, then
C-x o to switch windows. Emacs must not hang.
Stress test (line index):
25. Open a large file (>50,000 lines). Navigate to the end with
M-> or C-v repeatedly. VoiceOver speech should remain fluid
at all positions (no progressive slowdown).
26. Open an org-mode file with many folded sections. Verify that
folded (invisible) text is not announced during navigation.
REVIEW CHANGES (post initial implementation)
---------------------------------------------
The following changes were made based on maintainer-style code review:
1. ns_ax_window_end_charpos: added window_end_valid guard. Falls
back to BUF_ZV when the window has not been fully redisplayed,
preventing stale data in AX getters called before next redisplay.
2. GC safety documentation: detailed comment on lispWindow ivar
explaining why staticpro is not needed (windows reachable from
frame tree, GC only on main thread, AX getters dispatch to main).
3. ns-accessibility-enabled (DEFVAR_BOOL): new user option to
disable accessibility entirely. Guards three entry points.
4. postAccessibilityNotificationsForFrame: extracted from one ~200
line method into four focused helpers:
- postTextChangedNotification: (typing echo)
- postFocusedCursorNotification:direction:granularity:markActive:
oldMarkActive: (focused cursor/selection)
- postCompletionAnnouncementForBuffer:point: (completions)
- postAccessibilityNotificationsForFrame: (orchestrator, ~60 lines)
5. ns_ax_completion_text_for_span: added block_input/unblock_input
with specpdl unwind protection for signal safety.
6. Fplist_get third-argument comment (PREDICATE, not default value).
7. Documentation: macos.texi section updated with
ns-accessibility-enabled variable reference. etc/NEWS updated.
-- end of README --
Daneel
30089e9413