Subject: 28.2; Doc or behavior of replacement commands (e.g. `replace-string')
From: Drew Adams <[email-masked]>
To: "[email-masked]" <[email-masked]>
Date: Tue, 9 May 2023 20:13:04 +0000
List-Id: <debbugs-submit.debbugs.gnu.org>

emacs -Q

;; So `search-upper-case' is `not-yanks', and `case-fold-search' and
;; `case-replace' are both `t'.

In *scratch* enter this text:

Test 0
test 0

At bob, use `M-x replace-string RET test 0 RET test 1 RET'

(emacs) `Replacement and Lax Matches' seems to say that the result
should be this:

Test 1
test 1

But the result is this:

test 1
test 1

That doc says this:

  If the first argument of a replace command is all lower case, the
  command ignores case while searching for occurrences to replace-provided
  'case-fold-search' is non-'nil' and 'search-upper-case' is also
  non-'nil'.

OK, that's respected; both lines are found during the search.  Good.
___

BTW, it's unfortunate that we use an em dash char here, with no
preceding or following space chars.  Why?  Because it reads as if it
were a hyphen, producing adjective "replace-provided" modifying noun
`case-fold-search'.  Since we use fixed-width fonts by default, this is
all the more apparent.  Please reword or surround the em dash with space
chars.
___

The doc also says this, however, regarding replacement:

  In addition, when the NEWSTRING argument is all or partly lower case,
  replacement commands try to preserve the case pattern of each
  occurrence.  Thus, the command

     M-x replace-string <RET> foo <RET> bar <RET>

  replaces a lower case 'foo' with a lower case 'bar', an all-caps 'FOO'
  with 'BAR', and a capitalized 'Foo' with 'Bar'.  (These three
  alternatives-lower case, all caps, and capitalized, are the only ones
  that 'replace-string' can distinguish.)

My reading of this is that, since "test 1" is lower-case, the
replacement should "try" (meaning what, exactly? under what
circumstances does such a trial "fail"?) to preserve the case pattern of
the first occurrence, chaning "Test 0" to "Test 1".  That doesn't
happen.

Is the doc wrong?  Is my reading of it wrong?  If my reading and the doc
are right, is the behavior wrong (bugged)?
___

[It's also not very good to refer to argument NEWSTRING in a topic/node
that doesn't define it. Users have to look backward through the doc to
see if they can find out which argument this is talking about.]\
___

In GNU Emacs 28.2 (build 2, x86_64-w64-mingw32)
 of 2022-09-13 built on AVALON
Windowing system distributor 'Microsoft Corp.', version 10.0.19045
System Description: Microsoft Windows 10 Pro (v10.0.2009.19045.2846)

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