Comment by teddyh

11 hours ago

The problem with long lines was reportedly markedly improved in Emacs 29:

Emacs is now capable of editing files with very long lines. The display of long lines has been optimized, and Emacs should no longer choke when a buffer on display contains long lines. The variable 'long-line-threshold' controls whether and when these display optimizations are in effect.

A companion variable 'large-hscroll-threshold' controls when another set of display optimizations are in effect, which are aimed specifically at speeding up display of long lines that are truncated on display.

If you still experience slowdowns while editing files with long lines, this may be due to line truncation, or to one of the enabled minor modes, or to the current major mode. Try turning off line truncation with 'C-x x t', or try disabling all known slow minor modes with 'M-x so-long-minor-mode', or try disabling both known slow minor modes and the major mode with 'M-x so-long-mode', or visit the file with 'M-x find-file-literally' instead of the usual 'C-x C-f'.

In buffers in which these display optimizations are in effect, the 'fontification-functions', 'pre-command-hook' and 'post-command-hook' hooks are executed on a narrowed portion of the buffer, whose size is controlled by the variables 'long-line-optimizations-region-size' and 'long-line-optimizations-bol-search-limit', as if they were in a 'with-restriction' form. This may, in particular, cause occasional mis-fontifications in these buffers. Modes which are affected by these optimizations and by the fact that the buffer is narrowed, should adapt and either modify their algorithm so as not to expect the entire buffer to be accessible, or, if accessing outside of the narrowed region doesn't hurt performance, use the 'without-restriction' form to temporarily lift the restriction and access portions of the buffer outside of the narrowed region.

The new function 'long-line-optimizations-p' returns non-nil when these optimizations are in effect in the current buffer.