Improve documentation of line truncation and wrapping

* doc/emacs/display.texi (Line Truncation, Visual Line Mode):
* doc/lispref/display.texi (Truncation): Document that turning on
line truncation disables wrapping, and vice versa.

* src/buffer.c (syms_of_buffer) <truncate-lines>:
* src/xdisp.c (syms_of_xdisp) <truncate-partial-width-windows>:
Warn against turning on when 'visual-line-mode' is in effect.
* lisp/simple.el (visual-line-mode): Document that this mode
disables line truncation.  (Bug#29664)

2 files changed, 8 insertions, 2 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 100ebc7e2de..4eb7ab6d6ba 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -5805,7 +5805,10 @@ Note that this is overridden by the variable
 `truncate-partial-width-windows' if that variable is non-nil
 and this buffer is not full-frame width.
 
-Minibuffers set this variable to nil.  */);
+Minibuffers set this variable to nil.
+
+Don't set this to a non-nil value when `visual-line-mode' is
+turned on, as it could produce confusing results.   */);
 
   DEFVAR_PER_BUFFER ("word-wrap", &BVAR (current_buffer, word_wrap), Qnil,
                      doc: /* Non-nil means to use word-wrapping for continuation lines.
diff --git a/src/xdisp.c b/src/xdisp.c
index e853c8c2232..b2fcc165a9f 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -35136,7 +35136,10 @@ not span the full frame width.
 
 A value of nil means to respect the value of `truncate-lines'.
 
-If `word-wrap' is enabled, you might want to reduce this.  */);
+If `word-wrap' is enabled, you might want to reduce the value of this.
+
+Don't set this to a non-nil value when `visual-line-mode' is
+turned on, as it could produce confusing results.  */);
   Vtruncate_partial_width_windows = make_fixnum (50);
 
   DEFVAR_BOOL("word-wrap-by-category", word_wrap_by_category, doc: /*