using exec to close a fd in a var crashes bash

[jleivent]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -fstack-protector-strong -Wformat
-Werror=format-sec> uname output: Linux lapdog 6.1.0-11-amd64 #1 SMP
PREEMPT_DYNAMIC Debian 6.1.38-> Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.2
Patch Level: 15
Release Status: release

Description:
        Using exec to close a file descriptor in a variable crashes
        bash.  It doesn't matter how the fd got into the variable, but
        the likely usage is with the {varname} form, as illustrated
        below.  I think what is happening is that the exec arg is being
        parsed as a target to execute instead of a fd redirection,
        because when executed in two levels of shell (to allow the
        inner one to crash while leaving the outer), it generates the
        following error message:
                bash: exec: 10: not found
        But even that shouldn't cause the shell to terminate if the
        target isn't found, so maybe this is two bugs?
        
        Also note that the quoting and {} around foo in the last line
        don't impact the bug.

        This bug makes it difficult to use {varname} forms for file
        descriptors, as it means there is no easy way to close them
        before script exit.

Repeat-By:
        
        exec {foo}>/tmp/foo
        exec "${foo}"<&-