83352c4571
Replace the physical ekp-region renderer with ekp-buffer text-property projection backed by shared semantic layout plans and stable live-edit transactions. Optimize the C-backed resize hot path, and add deterministic performance, ERT, GUI, fuzz, release, and documentation coverage for task017 through task032. BREAKING CHANGE: require ekp-buffer instead of ekp-region and rename module-owned ekp-region-* settings to ekp-buffer-*.
91 lines
3.7 KiB
Markdown
91 lines
3.7 KiB
Markdown
# Own the Native Soft-Wrap Precondition
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## Context
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The native progressive editor deliberately lets Emacs decide when the
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active source line becomes another visual row. That model worked in a
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full-width verification window but failed in the user's narrow
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side-by-side window: the line horizontally scrolled and displayed a `$`
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truncation indicator.
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The source was clean and the KP planner was not involved. Emacs 30.2
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defaults `truncate-partial-width-windows` to `50`; a partial-width window
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below that many columns truncates even when `truncate-lines` is nil.
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Without a native visual row, the live engine has no completed row to
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observe or align.
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## Decision
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`ekp-auto-justify-mode` owns the display precondition its state machine
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requires:
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1. On activation, snapshot the values and buffer-local ownership of
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`truncate-lines` and `truncate-partial-width-windows`.
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2. Make both variables buffer-local and nil before the first reflow.
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3. On mode disable or major-mode teardown, restore prior local values or
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remove the temporary local bindings so global ownership resumes.
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4. Treat activation as a transaction: if width discovery, initial reflow,
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hook installation, or integration setup signals, remove partial
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lifecycle state, restore the display variables, set the mode back to
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disabled, and let the original error propagate.
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This changes only redisplay policy. It creates no source character,
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overlay, replacing display break, or independent wrapping algorithm.
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## Alternatives Rejected
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### Treat truncation as a user configuration error
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The failing value is an Emacs default in narrow split windows. A mode whose
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algorithm requires native visual rows cannot leave that precondition
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implicit and still promise natural editing.
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### Compute hidden visual rows while Emacs truncates
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That would make EKP simulate a display the user cannot see. It would also
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leave the reported horizontal-scrolling experience unchanged.
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### Set the variables without restoring them
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That would fix typing by permanently changing unrelated buffer behavior.
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Minor-mode ownership must end with the mode.
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### Change the global defaults
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The requirement belongs to one buffer while its auto mode is active.
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Changing global behavior would affect unrelated buffers and packages.
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## Consequences
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- Full-width and narrow side-by-side windows use the same native
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progressive state transitions.
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- Existing `visual-line-mode`/`word-wrap` behavior remains available;
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EKP only prevents truncation.
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- Disabling auto mode restores the exact prior buffer-local ownership.
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When the original state was global, removing the temporary binding lets
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the current global value resume.
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- Multiple windows showing the same buffer share the buffer-local
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soft-wrap policy, matching the existing buffer-wide projection model.
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## Verification
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A public minor-mode lifecycle ERT reproduces the failure red, then proves
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both variables are nil and buffer-local while enabled and that their prior
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local/global ownership is restored on disable. Separate regressions force
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initial reflow failure and switch major modes, proving those teardown paths
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restore the same ownership and never leave a half-enabled mode.
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The retained graphical run
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`/private/tmp/ekp-soft-wrap-final-pass-PIUigY` types mixed Latin/CJK text
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one character at a time in a 44-column left split. The selected window
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advances from one to two visual rows with `hscroll=0`, zero live replacing
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breaks, zero overlays, exact source text, and no pending transaction.
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Temporal review finds only the intended Emacs split, natural continuation,
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and a stable final frame.
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## Rollback
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Revert the wrap-state snapshot, activation, and restoration together.
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Leaving only the forced values or only the restoration would violate mode
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ownership.
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