Fix order of checking ICU options in initdb and create database

Hello!

This is the last proposed patch on this subject [1] moved to a separate
thread for Commitfest..

It looks like that the current order of checking ICU options in initdb
and create database in PG 15+ is not user-friendly. Examples:

1. initdb reports a missing ICU locale although it may already report
that the selected encoding cannot be used:

$ initdb --encoding sql-ascii --locale-provider icu hoge
...
initdb: error: ICU locale must be specified

$ initdb --encoding sql-ascii --locale-provider icu --icu-locale en-US
hoge
...
initdb: error: encoding mismatch
initdb: detail: The encoding you selected (SQL_ASCII) is not supported
with the ICU provider.
initdb: hint: Rerun initdb and either do not specify an encoding
explicitly, or choose a matching combination.

2. initdb/create database report problems with the ICU locale/encoding
although they may already report that ICU is not supported in this
build:

2.1.

$ initdb --locale-provider icu hoge
...
initdb: error: ICU locale must be specified

$ initdb --locale-provider icu --icu-locale en-US hoge
...
initdb: error: ICU is not supported in this build

$ createdb --locale-provider icu hoge
createdb: error: database creation failed: ERROR: ICU locale must be
specified

$ createdb --locale-provider icu --icu-locale en-US hoge
createdb: error: database creation failed: ERROR: ICU is not supported
in this build

2.2.

$ createdb --locale-provider icu --icu-locale en-US --encoding sql-ascii
hoge
createdb: error: database creation failed: ERROR: encoding "SQL_ASCII"
is not supported with ICU provider

$ createdb --locale-provider icu --icu-locale en-US --encoding utf8 hoge
createdb: error: database creation failed: ERROR: ICU is not supported
in this build

The patch
v1-0001-Fix-order-of-checking-ICU-options-in-initdb-and-c.patch fixes
this:

1.

$ initdb --encoding sql-ascii --locale-provider icu hoge
...
initdb: error: encoding mismatch
initdb: detail: The encoding you selected (SQL_ASCII) is not supported
with the ICU provider.
initdb: hint: Rerun initdb and either do not specify an encoding
explicitly, or choose a matching combination.

2.1.

$ initdb --locale-provider icu hoge
...
initdb: error: ICU is not supported in this build

$ createdb --locale-provider icu hoge
createdb: error: database creation failed: ERROR: ICU is not supported
in this build

2.2.

$ createdb --locale-provider icu --icu-locale en-US --encoding sql-ascii
hoge
createdb: error: database creation failed: ERROR: ICU is not supported
in this build

A side effect of the proposed patch in initdb is that if ICU locale is
missed (or ICU is not supported in this build), the provider, locales
and encoding are reported before the error message:

$ initdb --locale-provider icu hoge
The files belonging to this database system will be owned by user
"marina".
This user must also own the server process.

The database cluster will be initialized with this locale configuration:
provider: icu
LC_COLLATE: en_US.UTF-8
LC_CTYPE: en_US.UTF-8
LC_MESSAGES: en_US.UTF-8
LC_MONETARY: ru_RU.UTF-8
LC_NUMERIC: ru_RU.UTF-8
LC_TIME: ru_RU.UTF-8
The default database encoding has been set to "UTF8".
initdb: error: ICU locale must be specified

$ initdb --locale-provider icu hoge
The files belonging to this database system will be owned by user
"marina".
This user must also own the server process.

The database cluster will be initialized with this locale configuration:
provider: icu
LC_COLLATE: en_US.UTF-8
LC_CTYPE: en_US.UTF-8
LC_MESSAGES: en_US.UTF-8
LC_MONETARY: ru_RU.UTF-8
LC_NUMERIC: ru_RU.UTF-8
LC_TIME: ru_RU.UTF-8
The default database encoding has been set to "UTF8".
initdb: error: ICU is not supported in this build

I was thinking about another master-only version of the patch that first
checks everything for provider, locales and encoding but IMO it is worse
[2]..

[1]
https://www.postgresql.org/message-id/e94aca035bf0b92fac42d204ad385552%40postgrespro.ru
[2]
https://www.postgresql.org/message-id/79f410460c4fc9534000785adb8bf39a%40postgrespro.ru

--
Marina Polyakova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company