[Go target] Fix for #3926: Add accessors for tree navigation to interfaces in generated parser

[j3r3miah]

What does this PR fix?

• [Go target] Generated parser contains interfaces without requisite methods for tree navigation #3926

Discussion

This is an attempt to remove the need to always cast these interfaces to concrete types. I considered two options:

1. Update accessors to return concrete types instead of interfaces
2. Add the missing method signatures to the existing interfaces

This PR implements option (2), as (1) would be a breaking change for existing applications. I believe (2) is backwards compatible.

The strategy here is to add a flag, signature, to each of the ContextGetterDecl subclasses so that each of their corresponding template definitions can conditionally generate a method signature (for the interface) versus the complete method declaration.

The getSignatureDecl() functions on each of the ContextGetterDecl subclasses are pretty tedious... open to suggestions for a more elegant option...

Grammar

abb

module  : moduleData EOF   ;
moduleData : MODULE moduleName NEWLINE  dataList  NEWLINE* ENDMODULE ;

Before this change

Generated Go

func (p *abbParserParser) Module() (localctx IModuleContext) { ... }
func (s *ModuleContext) ModuleData() IModuleDataContext { ... }

type IModuleDataContext interface {
	antlr.ParserRuleContext

	// GetParser returns the parser.
	GetParser() antlr.Parser

	// IsModuleDataContext differentiates from other interfaces.
	IsModuleDataContext()
}

type ModuleDataContext struct {
	*antlr.BaseParserRuleContext
	parser antlr.Parser
}

Navigation in Go

module.(*parser.ModuleContext).ModuleData().(*parser.ModuleDataContext).ModuleName()

After this change

Generated Go

func (p *abbParserParser) Module() (localctx IModuleContext) { ... }
func (s *ModuleContext) ModuleData() IModuleDataContext { ... }

type IModuleDataContext interface {
    antlr.ParserRuleContext

    // GetParser returns the parser.
    GetParser() antlr.Parser

    // Getter signatures
    MODULE() antlr.TerminalNode
    ModuleName() IModuleNameContext
    AllNEWLINE() []antlr.TerminalNode
    NEWLINE(i int) antlr.TerminalNode
    DataList() IDataListContext
    ENDMODULE() antlr.TerminalNode

    // IsModuleDataContext differentiates from other interfaces.
    IsModuleDataContext()
}

type ModuleDataContext struct {
	*antlr.BaseParserRuleContext
	parser antlr.Parser
}

Navigation in Go

module.ModuleData().ModuleName()

Why is this PR important?

This change increases the usability of the Go parsers. Without this change, code littered with type assertions is difficult to read/maintain.

[j3r3miah]

Hi @jimidle, I'd appreciate your review here

[jimidle]

I will look at this today. I notice one check does not pass though. We will need that to pass. On the face of it, this looks like the correct thing to generate

[j3r3miah]

Thanks, @jimidle. I saw that failure as well - it looks like infra flake to me. It passed on the next commit.

[j3r3miah]

Hey @jimidle, I'd appreciate that review when you have a chance. Thank you!

[kaby76]

Looks wonderful. The generated code is exactly what we need, and mirrors what the other targets do. @parrt

[parrt]

I can't tell if it's backward compatible...i don't wanna break code in google. ;)

I'll wait for @jimidle to sign off on this but looks better.

[j3r3miah]

The only breaking scenario I can imagine is if user code is relying on implementing the parser-generated interfaces for some reason, which seems unlikely - but I'll defer to the experts! Thankya.

[jimidle]

@parrt We can merge this PR - it will not break anything as far as I can see.

[parrt]

Thanks @jimidle !

[parrt]

@perezd this should help the visitor, if you have time to check.

[KvanTTT]

If I understand correctly, it should be marked with final.

[KvanTTT]

No need to use getter method if signature is final.

[j3r3miah]

Good call: #3947