allow datafusion cli to take -- comments

[jimexist]

Which issue does this PR close?

Closes #297.

Rationale for this change

-- comments shall be respected in parsing command line input

What changes are included in this PR?

• adding support for -- for both file and cli mode

Are there any user-facing changes?

If there are user-facing changes then we may require documentation to be updated before approving the PR.

If there are any breaking changes to public APIs, please add the breaking change label.

[jimexist]

❯ cargo run --release --bin datafusion-cli -q
> -- hello
> select 1 num;
+-----+
| num |
+-----+
| 1   |
+-----+
1 rows in set. Query took 0 seconds.

[codecov-commenter]

Codecov Report

Merging #296 (5e1b074) into master (204d4f5) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
- Coverage   75.99%   75.98%   -0.01%     
==========================================
  Files         141      141              
  Lines       23657    23659       +2     
==========================================
  Hits        17978    17978              
- Misses       5679     5681       +2     

Impacted Files	Coverage Δ
datafusion-cli/src/main.rs	0.00% <0.00%> (ø)

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[msathis]

LGTM

[jorgecarleitao]

Thanks @jimexist ; nice and sweet.

[Dandandan]

I am wondering, can't we fix the code so comments are parsed correctly rather than skipping them?
I believe you might be able to change the code to add new lines rather than a space at the end of every line.

query.push(' ');
// To
query.push('\n');

This way we should also parse multiline comments, comments starting with a space, etc correctly.

[jimexist]

I am wondering, can't we fix the code so comments are parsed correctly rather than skipping them?
I believe you might be able to change the code to add new lines rather than a space at the end of every line.

query.push(' ');
// To
query.push('\n');

This way we should also parse multiline comments, comments starting with a space, etc correctly.

@Dandandan thanks for the advise. i've updated the appending to use \n instead.

However I still think we shall skip -- starting lines like the changes i made here, otherwise a line with -- ; will result in an error

[Dandandan]

I am wondering, can't we fix the code so comments are parsed correctly rather than skipping them?
I believe you might be able to change the code to add new lines rather than a space at the end of every line.

query.push(' ');
// To
query.push('\n');

This way we should also parse multiline comments, comments starting with a space, etc correctly.

@Dandandan thanks for the advise. i've updated the appending to use \n instead.

However I still think we shall skip -- starting lines like the changes i made here, otherwise a line with -- ; will result in an error

Fair enough, thanks! I think at some point we should remove the ; check and work together with the parser to detect true statement endings. Untill then this seems a good compromise.

[jimexist]

Agreed that this is a compromise - at least writing multiple semicolons will still break A