Problem in var substitution with / and \

[Jean-François Berroyer]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu 


Compiler: gcc
Compilation CFLAGS: -march=x86-64 -mtune=generic -O2 -pipe 
-fstack-protector-strong -fno-plt 
-DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/bin' 
-DSTANDARD_UTILS_PATH='/usr/bin' -DSYS_BASHRC='/etc/ba>
uname output: Linux euler 4.20.0-arch1-1-ARCH #1 SMP PREEMPT Mon Dec 24 
03:00:40 UTC 2018 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.0
Patch Level: 0
Release Status: release

Description:
If a variable contains one '/' (or many)
and if this '/' is escaped with '\' by substitution mechanism
and if the escaped variable is concatenated with a string containing '/' 
as prefix, and another string containing '/' as suffix
then all characters in prefix and suffix are escaped with '\'
The problem does not occurs in a "" context

Repeat-By:
URL=http://example.com
ESCAPED_URL=${URL//\//\\\/}
echo 'My URL: '$ESCAPED_URL' ... OK'
echo '/My URL: http:\/\/example.com ... OK/'
echo "/My URL: $ESCAPED_URL ... OK/"
echo '/My URL: '$ESCAPED_URL' ... KO/'