Add basic support for GRANT and REVOKE

[blx]

Hello 👋

Preliminary PR here for basic GRANT and REVOKE support. I'm not sure if permissions statements like GRANT are in scope here; if not please feel free to close!

My personal experience is mostly postgres-flavored but I've tried to stick to the spec here. Note, this only addresses granting privileges regarding objects (like tables); there is also a GRANT <role_name> TO <role_specification> for adding users to groups, which is not considered here.

This also doesn't yet consider column permissions (GRANT SELECT ON a (id, created) ...), nor other object types like DATABASE or DOMAIN.

Please let me know if there's interest in this, thanks!

[alamb]

Thank you @blx -- sorry for the lengthy delay -- I didn't see this PR until recently.

I think this PR is well constructed and well tested.

[alamb]

Maybe worth removing it from the struct then?

[blx]

@alamb I erred on the side of losslessness here, but I wasn't sure to what degree that's a goal.

I guess there are already many cases where an implied default becomes explicit when parsed, and would then produce different output after a roundtrip if the input had omitted the default (eg. cascade in Statement::Drop).

If you think it would be cleaner I'm happy to PR removing this.

[alamb]

If this field is needed to survive the round trip I think keeping it makes sense.

[coveralls]

Pull Request Test Coverage Report for Build 1452484256

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 237 of 284 (83.45%) changed or added relevant lines in 3 files are covered.
• 37 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-0.6%) to 89.674%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	65	80	81.25%
src/parser.rs	62	94	65.96%

Files with Coverage Reduction	New Missed Lines	%
src/ast/data_type.rs	1	76.32%
src/ast/query.rs	1	87.08%
src/ast/value.rs	1	86.67%
src/ast/ddl.rs	2	81.67%
src/ast/mod.rs	5	73.16%
src/tokenizer.rs	7	90.61%
src/parser.rs	20	84.09%

Totals
Change from base Build 1342693636:	-0.6%
Covered Lines:	6018
Relevant Lines:	6711

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💛 - Coveralls

[alamb]

@blx I merged your code to master and fixed some clippy warnings