TINKERPOP-3248: Added Character support in gremlin-go

[Iryna-Kahamlyk]

JIRA: https://issues.apache.org/jira/browse/TINKERPOP-3248

Summary

Adds support for the Gremlin Character type to gremlin-go, in both GremlinLang text generation and GraphBinary serialization.

Go's rune is only an alias for int32, so it can't be distinguished from an int in a type switch. This introduces a new exported type, Char, that callers use to explicitly mark a value as a Character (e.g. g.Inject(gremlingo.Char('a'))).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.70%. Comparing base (a28cd1f) to head (fd043c7).
⚠️ Report is 645 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3673      +/-   ##
============================================
+ Coverage     76.35%   76.70%   +0.34%     
- Complexity    13424    14336     +912     
============================================
  Files          1012     1037      +25     
  Lines         60341    64797    +4456     
  Branches       7075     7695     +620     
============================================
+ Hits          46076    49704    +3628     
- Misses        11548    11999     +451     
- Partials       2717     3094     +377     

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[GumpacG]

Can you update gremlin-variants.asciidoc as it still states character is a limitation of Go.

Can you also add or enable feature tests for char in cucumberSteps_test.go?

[GumpacG]

I think we should consider naming this type Char rune. This way users would call g.Inject(gremlingo.Char('a')) instead of g.Inject(gremlingo.Rune('a')). The package already names this Gremlin type GType.Char and the internals here are already char-based (charType, charWriter, readChar), so Char would keep the naming consistent.

[Iryna-Kahamlyk]

Thanks for pointing that out. All done!

[GumpacG]

VOTE +1

[kenhuuu]

I think we should probably add some more cases here like we did with gremlin-python:

Char('\\')      // g.inject("\\"c)
Char('\'')      // g.inject("'"c)
Char('\n')      // g.inject("\n"c)
rune('a')       // g.inject(97), confirming rune remains Int

[kenhuuu]

I think we should have more tests here too. same as the ones I said with gremlinlang

"a"c
"\""c
"\\"c
"'"c
'\''c

that last one is particularly important because I think it might be a bug.

// Current, invalid Go
gremlingo.Char(''')

// Required
gremlingo.Char('\'')

also, Gremlin supports one- and two-digit octal escapes

"\7"c
"\07"c

[kenhuuu]

You might want to write here how the new Char type behaves. That is, users of gremlin-go that try something like g.inject('a') will lead to it being intepreted as an Integer. They have to use the new Char type that wraps a Rune to get the GremlinLang to actually generate a Char type.