https://issues.dlang.org/show_bug.cgi?id=13523

          Issue ID: 13523
           Summary: Auto function declaration does not match any grammar
                    rule
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P1
         Component: websites
          Assignee: nobody@puremagic.com
          Reporter: k.hara.pg@gmail.com

auto foo() {}

It is a function declaration with return type inference, but surprisingly, the syntax does not match any documented grammar rule.

Decl:
    StorageClasses_opt BasicType Declarators ;
    StorageClasses_opt BasicType Declarator FunctionBody

--> BasicType is not optional, so cannot match

AutoDeclaration:
    StorageClasses AutoDeclarationX ;

AutoDeclarationX:
    Identifier TemplateParametersopt = Initializer
    AutoDeclarationX , Identifier TemplateParametersopt = Initializer

--> This is for variable declarations with type inference, not for function declaration.

So, the specification should have one more non-terminal symbol AutoFuncDeclaration, as follows:

AutoFuncDeclaration:
    StorageClasses Identifier FuncDeclaratorSuffix FunctionBody

FuncDeclaratorSuffix:
    Parameters MemberFunctionAttributes_opt
    TemplateParameters Parameters MemberFunctionAttributes_opt Constraint_opt

--