bug#67210: 30.0.50; completing-read with REQUIRE-MATCH=t can sometimes return a non-match

[Spencer Baugh]

1. emacs -Q
2. (completing-read ":" '("foo") nil t '("foobar" . 3))
3. RET
4. See "foobar", i.e. "foobar" was accepted as input despite not being
   in the collection we're completing over.

I believe this is because
(completion-try-completion "foobar" '("foo") nil 3)
returns t, which completion--do-completion interprets as meaning that
the input string is an "Exact and unique match."

That t is returned because
(completion-emacs22-try-completion "foobar" '("foo") nil 3)
returns t.

So perhaps completion--do-completion is wrong in assuming that a t
return value from completion-try-completion indicates an "Exact and
unique match."?

Or perhaps completion-emacs22-try-completion is violating the spec of
completion-try-completion, and should be returning nil in this case?


In GNU Emacs 30.0.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version
 3.22.30, cairo version 1.15.12) of 2023-11-15 built on igm-qws-u22796a
Repository revision: 1a1f47e4a1fb70e6810f9eabd0f1826b71a2bcb0
Repository branch: project-history
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Rocky Linux 8.8 (Green Obsidian)

Configured using:
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Load-path shadows:
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Features:
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Memory information:
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