Add config CLI argument to lint, fix, and parse

[jpy-git]

Brief summary of the change made

Fixes #1244.
This PR adds a command line argument --config to the CLI lint, fix, and parse commands.

The user can specify an additional config file such that the override logic is (later files override earlier ones):

• default_config.cfg (package default)
• <user_appdir_configs>
• <user_homedir_configs>
• <user_homedir_configs>
• <configs_between_cwd_and_sql_path>
• <extra_config_file> (this PR)
• Any command line arguments

This behaviour was voted on in the Slack channel: https://sqlfluff.slack.com/archives/C01GPHR8J0G/p1637859667129900

If no config files are included in the default config search paths then this argument can be used to specify a single off-path config file which will also be useful for several applications.
(Will investigate in a future PR adding --ignore-local-config option to allow only --config to be considered)

N.B. This PR focuses on the CLI, I will make a subsequent PR to flow the changes through to the Simple API as well.

Are there any other side effects of this change that we should be aware of?

No

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with python test/generate_parse_fixture_yml.py or by running tox locally).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[codecov]

Codecov Report

Merging #1986 (997622b) into main (d145358) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1986   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          148       148           
  Lines        10292     10305   +13     
=========================================
+ Hits         10292     10305   +13     

Impacted Files	Coverage Δ
src/sqlfluff/cli/commands.py	100.00% <100.00%> (ø)
src/sqlfluff/core/config.py	100.00% <100.00%> (ø)
src/sqlfluff/core/linter/linter.py	100.00% <100.00%> (ø)

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[tunetheweb]

LGTM but how do we know that the extra config is being used? Tests don't seem to check that.

Also test/fixtures/cli/extra_config_tsql.sql is empty which looks a little odd.

Maybe we could fix both concerns by adding some T-SQL specific SQL that fails in ANSI to check the dialect has indeed been changed as per the extra config?

[jpy-git]

@tunetheweb weird that's exactly what the test was! Not sure how it didn't commit that sql but will add it back in now 😄

[jpy-git]

@tunetheweb I've re-added that missing unit test back in 👍