gencpp/docs/Parser_Algo.md

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Parser's Algorithim

gencpp uses a hand-written recursive descent parser. Both the lexer and parser currently handle a full C/C++ file in a single pass.

Notable implementation background

Lexer

File: lexer.cpp

The lex procedure does the lexical pass of content provided as a Str type.
The tokens are stored (for now) in Lexer_Tokens.

Fields:

Array<Token> Arr;
s32          Idx;

What token types are supported can be found in ETokType.csv you can also find the token types in ETokType.h , which is the generated enum from the csv file.

struct Token
{
    Str     Text;
    TokType Type;
    s32     Line;
    s32     Column;
    u32     Flags;
}

Flags is a bitfield made up of TokFlags (Token Flags):

• TF_Operator : Any operator token used in expressions
• TF_Assign
  • Using statment assignment
  • Parameter argument default value assignment
  • Variable declaration initialization assignment
• TF_Preprocess : Related to a preprocessing directive
• TF_Preprocess_Cond : A preprocess conditional
• TF_Attribute : An attribute token
• TF_AccessSpecifier : An accesor operation token
• TF_Specifier : One of the specifier tokens
• TF_EndDefinition : Can be interpreted as an end definition for a scope.
• TF_Formatting : Considered a part of the formatting
• TF_Literal : Anything considered a literal by C++.
• TF_Macro_Functional : Used to indicate macro token is flagged as MF_Functional.
• TF_Macro_Expects_Body : Used to indicate macro token is flagged as MF_Expects_Body.

Parser

Files:

• interface.parsering.cpp
• parser.cpp

The parser has a limited user interface, only specific types of definitions or statements are expected to be provided by the user directly when using to construct an AST dynamically. It however does attempt to provide capability to parse a full C/C++ from production codebases.

Each public user interface procedure has the following format:

<code type> parse_<definition type>( Str def )
{
    check_parse_args( def );
    using namespace Parser;

    TokArray toks = lex( def );
    if ( toks.Arr == nullptr )
        return CodeInvalid;

    // Parse the tokens and return a constructed AST using internal procedures
    ...
}

The most top-level parsing procedure used for C/C++ file parsing is parse_global_body.
It uses a helper procedure called parse_global_nspace.

Each internal procedure will have the following format:

internal
<code type> parse_<definition_type>( <empty or contextual params> )
{
    push_scope();

    ...

    <code type> result = (<code type>) make_code();
    ...

    Context.pop();
    return result;
}

The parsing implementation contains throughut the codeapths to indicate how far their contextual AST node has been resolved.

Example:

internal
CodeFn parser_parse_function()
{
    push_scope();

    Specifier specs_found[16] = { Spec_NumSpecifiers };
    s32        NumSpecifiers = 0;

    CodeAttributes attributes = { nullptr };
    CodeSpecifiers specifiers = { nullptr };
    ModuleFlag     mflags     = ModuleFlag_None;

    if ( check(Tok_Module_Export) ) {
        mflags = ModuleFlag_Export;
        eat( Tok_Module_Export );
    }
    // <export>

    attributes = parse_attributes();
    // <export> <Attributes>

    while ( left && tok_is_specifier(currtok) )
    {
        Specifier spec = str_to_specifier( tok_to_str(currtok) );

        switch ( spec )
        {
            GEN_PARSER_FUNCTION_ALLOWED_SPECIFIER_CASES:
            break;

            default:
                log_failure( "Invalid specifier %S for functon\n%SB", spec_to_str(spec), parser_to_strbuilder(_ctx->parser) );
                parser_pop(& _ctx->parser);
                return InvalidCode;
        }

        if ( spec == Spec_Const )
            continue;

        specs_found[NumSpecifiers] = spec;
        NumSpecifiers++;
        eat( currtok.Type );
    }

    if ( NumSpecifiers ) {
        specifiers = def_specifiers_arr( NumSpecifiers, specs_found );
    }
    // <export> <Attributes> <Specifiers>

    CodeTypename ret_type = parser_parse_type(parser_not_from_template, nullptr);
    if ( cast(Code, ret_type) == Code_Invalid ) {
        parser_pop(& _ctx->parser);
        return InvalidCode;
    }
    // <export> <Attributes> <Specifiers> <ReturnType>

    Token name = parse_identifier(nullptr);
    _ctx->parser.Scope->Name = name.Text;
    if ( ! tok_is_valid(name) ) {
        parser_pop(& _ctx->parser);
        return InvalidCode;
    }
    // <export> <Attributes> <Specifiers> <ReturnType> <Name>

    CodeFn result = parse_function_after_name( mflags, attributes, specifiers, ret_type, name );
    // <export> <Attributes> <Specifiers> <ReturnType> <Name> ...

    parser_pop(& _ctx->parser);
    return result;
}

In the above parse_function implementation:

// <intutive expression of AST component> ...

Will be conventionlly used where by that point in time for the codepath: <intutive expression of AST component> should be resolved for the AST.

Outline of parsing codepaths

Below is an outline of the general alogirithim used for these internal procedures. The intention is to provide a basic briefing to aid the user in traversing the actual code definitions. These appear in the same order as they are in the parser.cpp file

NOTE: This is still heavily in an alpha state. A large swaph of this can change, make sure these docs are up to date before considering them 1:1 with the repo commit your considering.

parse_array_decl

1. Push parser scope
2. Check for empty array []
   1. Return untyped string with single space if found
3. Check for opening bracket [
   1. Validate parser not at EOF
   2. Reject empty array expression
   3. Capture expression tokens until closing bracket
   4. Calculate expression span length
   5. Convert to untyped string
4. Validate and consume closing bracket ]
5. Handle multi-dimensional case
   1. If adjacent [ detected, recursively parse
   2. Link array expressions via Next pointer
6. Pop parser scope
7. Return array expression or NullCode on failure

parse_attributes

1. Push parser scope and initialize tracking
   1. Store initial token position
   2. Initialize length counter
2. Process attributes while available
   1. Handle C++ style attributes [[...]]
      1. Consume opening [[
      2. Capture content until closing ]]
      3. Calculate attribute span length
   2. Handle GNU style __attribute__((...))
      1. Consume __attribute__ keyword and opening ((
      2. Capture content until closing ))
      3. Calculate attribute span length
   3. Handle MSVC style __declspec(...)
      1. Consume __declspec and opening (
      2. Capture content until closing )
      3. Calculate attribute span length
   4. Handle macro-style attributes
      1. Consume attribute token
      2. If followed by parentheses
         1. Handle nested parentheses tracking
         2. Capture content maintaining paren balance
      3. Calculate attribute span length
3. Generate attribute code if content captured
   1. Create attribute text span from start position and length
   2. Strip formatting from attribute text
   3. Construct Code node
      1. Set type to CT_PlatformAttributes
      2. Cache and set Name and Content fields
   4. Return as CodeAttributes
4. Pop parser scope
5. Return NullCode if no attributes found

parse_class_struct

1. Validate token type is class or struct
   1. Return InvalidCode if validation fails
2. Initialize class/struct metadata
   1. Access specifier (default)
   2. Parent class/struct reference
   3. Class/struct body
   4. Attributes
   5. Module flags
3. Parse module export flag if present
   1. Set ModuleFlag_Export
   2. Consume export token
4. Consume class/struct token
5. Parse attributes via parse_attributes()
6. Parse class/struct identifier
   1. Update parser scope name
7. Initialize interface array (4KB arena)
8. Parse inheritance/implementation
   1. If classifier token (:) present
      1. Parse access specifier if exists
      2. Parse parent class/struct name
      3. Parse additional interfaces
         1. Separated by commas
         2. Optional access specifiers
         3. Store in interface array
9. Parse class body if present
   1. Triggered by opening brace
   2. Parse via parse_class_struct_body
10. Handle statement termination
    1. Skip for inplace definitions
    2. Consume semicolon
    3. Parse inline comment if present
11. Construct result node
    1. Create class definition if Tok_Decl_Class
    2. Create struct definition if Tok_Decl_Struct
    3. Attach inline comment if exists
12. Cleanup interface array and return result

parse_class_struct_body

1. Initialize scope and body structure
   1. Push parser scope
   2. Consume opening brace
   3. Create code node with CT_Class_Body or CT_Struct_Body type
2. Parse body members while not at closing brace
   1. Initialize member parsing state
      1. Code member (InvalidCode)
      2. Attributes (null)
      3. Specifiers (null)
      4. Function expectation flag
   2. Handle preprocessor hash if present
   3. Process member by token type in switch statement
      1. Statement termination - warn and skip
      2. Newline - format member
      3. Comments - parse comment
      4. Access specifiers - public/protected/private
      5. Declarations - class/enum/struct/union/typedef/using
      6. Operators - destructors/casts
      7. Preprocessor directives - define/include/conditionals/pragmas
      8. Preprocessor statement macros
      9. Report naked preprocossor expression macros detected as an error.
      10. Static assertions
      11. Attributes and specifiers
          1. Parse attributes
          2. Parse valid member specifiers
          3. Handle attribute-specifier-attribute case
      12. Identifiers and types
          1. Check for constructors
          2. Parse operator/function/variable
      13. Default - capture unknown content until closing brace
   4. Validate member parsing
      1. Return InvalidCode if member invalid
      2. Append valid member to body
3. Finalize body
   1. Consume closing brace
   2. Pop parser scope
   3. Return completed CodeBody

parse_comment

1. Just wrap the token into a cached string ( the lexer did the processing )

parse_complicated_definition

1. Initialize parsing context
   1. Push scope
   2. Set inplace flag false
   3. Get token array reference
2. Scan ahead for statement termination
   1. Track brace nesting level
   2. Find first semicolon at level 0
3. Handle declaration variants
   1. Forward declaration case
      1. Check if only 2 tokens before semicolon
      2. Parse via parse_forward_or_definition
   2. Function with trailing specifiers
      1. Identify trailing specifiers
      2. Check for function pattern
      3. Parse as operator/function/variable
      4. Return InvalidCode if pattern invalid
   3. Identifier-based declarations
      1. Check identifier patterns
         1. Inplace definition {...} id;
         2. Namespace type variable which id id;
         3. Enum with class qualifier
         4. Pointer/reference types
      2. Parse as operator/function/variable if valid
      3. Return InvalidCode if pattern invalid
   4. Basic type declarations
      1. Validate enum class pattern
      2. Parse via parser_parse_enum
      3. Return InvalidCode if invalid
   5. Direct definitions
      1. Handle closing brace - parse_forward_or_definition
      2. Handle array definitions - parse_operator_function_or_variable
      3. Return InvalidCode for unknown patterns

parse_assignment_expression

1. Initialize expression parsing
   1. Null expression pointer
   2. Consume assignment operator token
   3. Capture initial expression token
2. Validate expression presence
   1. Check for immediate termination
   2. Return InvalidCode if missing expression
3. Parse balanced expression
   1. Track nesting level for
      1. Curly braces
      2. Parentheses
   2. Continue until
      1. End of input, or
      2. Statement terminator, or
      3. Unnested comma
   3. Consume tokens sequentially
4. Generate expression code
   1. Calculate expression span length
   2. Convert to untyped string
   3. Return expression node

parse_forward_or_definition

1. Declaration type routing
   1. Class (Tok_Decl_Class) -> parser_parse_class
   2. Enum (Tok_Decl_Enum) -> parser_parse_enum
   3. Struct (Tok_Decl_Struct) -> parser_parse_struct
   4. Union (Tok_Decl_Union) -> parser_parse_union
2. Error handling
   1. Return InvalidCode for unsupported token types
   2. Log failure with parser context

is_inplace flag propagates to specialized codepaths to maintain parsing context.

parse_function_after_name

This is needed as a function defintion is not easily resolvable early on, as such this function handles resolving a function after its been made ceratin that the type of declaration or definition is indeed for a function signature.

By the point this function is called the following are known : export module flag, attributes, specifiers, return type, & name

1. Parameter parsing
   1. Push scope
   2. Parse parameter list with parentheses
2. Post-parameter specifier processing
   1. Collect trailing specifiers
   2. Initialize or append to existing specifiers
3. Parse function termination
   1. Function body case
      1. Parse body if open brace found
      2. Validate body type (CT_Function_Body or CT_Untyped)
   2. Pure virtual case
      1. Handle "= 0" syntax
      2. Append pure specifier
   3. Forward declaration case
      1. Consume statement terminator
   4. Handle inline comments for all cases
4. Construct function node
   1. Strip whitespace from name
   2. Initialize CodeFn with base properties
      1. Name (cached, stripped)
      2. Module flags
   3. Set node type
      1. CT_Function if body present
      2. CT_Function_Fwd if declaration only
   4. Attach components
      1. Attributes if present
      2. Specifiers if present
      3. Return type
      4. Parameters if present
      5. Inline comment if present
5. Cleanup and return
   1. Pop scope
   2. Return completed function node

parse_function_body

Currently there is no actual parsing of the function body. Any content with the braces is shoved into an execution AST node. In the future statements and expressions will be parsed.

1. Initialize body parsing
   1. Push scope
   2. Consume opening brace
   3. Create CodeBody with CT_Function_Body type
2. Capture function content
   1. Record start token position
   2. Track brace nesting level
   3. Consume tokens while
      1. Input remains AND
      2. Not at unmatched closing brace
   4. Update level counters
      1. Increment on open brace
      2. Decrement on closing brace when level > 0
3. Process captured content
   1. Calculate content length via pointer arithmetic
   2. Create execution block if content exists
      1. Construct string span from start position and length
      2. Wrap in execution node
      3. Append to body
4. Finalize
   1. Consume closing brace
   2. Pop scope
   3. Return cast body node

parse_global_nspace

1. State initialization
   1. Push parser scope
   2. Validate namespace type (Global, Namespace, Export, Extern Linkage)
   3. Consume opening brace for non-global scopes
   4. Initialize CodeBody with specified body type: which
2. Member parsing loop (while not at closing brace)
   1. Reset parse state
      • Member code
      • Attributes
      • Specifiers
      • Function expectation flag
   2. Member type handling
      1. Declarations
         • Class/Struct/Union/Enum via parse_complicated_definition
         • Template/Typedef/Using via dedicated parsers
         • Namespace/Export/Extern declarations
      2. Preprocessor directivess
         • Include/Define
         • Conditionals (if / ifdef / ifndef / elif / else / endif)
         • Pragmas
         • Preprocessor statement macros
         • Report naked preprocossor expression macros detected as an error.
      3. Comments/Formatting
         • Newlines
         • Comments
      4. Static assertions
   3. Attributes and specifiers
      1. Parse attributes if present
      2. Collect valid specifiers (max 16)
      3. Handle consteval for function expectation
   4. Identifier resolution
      1. Check constructor/destructor implementation
      2. Look ahead for user defined operator implementation outside of class
      3. Default to operator/function/variable parse
3. Member validation/storage
   1. Validate parsed member
   2. Append to body if valid
   3. Return InvalidCode on parse failure
4. Scope finalization
   1. Consume closing brace for non-global scopes
   2. Pop parser scope
   3. Return completed body

parse_global_nspace_constructor_destructor

1. Forward Token Analysis
   1. Scan for parameter list opening parenthesis
   2. Template Expression Handling
      • Track template nesting depth
      • Account for nested parentheses within templates
      • Skip until template closure or parameter start

      // Valid patterns:
      ClassName          ::  ClassName(...)
      ClassName          :: ~ClassName(...)
      ClassName< T ... > ::  ClassName(...)

2. Constructor/Destructor Identification
   1. Token Validation Sequence
      • Verify identifier preceding parameters
      • Check for destructor indicator (~)
      • Validate scope resolution operator (::)
   2. Left-side Token Analysis
      • Process nested template expressions
      • Maintain template/capture level tracking
      • Locate matching identifier token
3. Parser Resolution
   1. Name Pattern Validation
      • Compare identifier tokens for exact match
   2. Specialized Parsing
      • Route to parser_parse_destructor for '~' prefix
      • Route to parser_parse_constructor for direct match
   3. Apply specifiers to resulting node
4. Return result (NullCode on pattern mismatch)

Implementation Constraints

• Cannot definitively distinguish nested namespaces with identical names
• Return type detection requires parser enhancement
• Template parameter validation is syntax-based only
• Future enhancement: Implement type parsing with rollback capability

parse_identifier

This is going to get heavily changed down the line to have a more broken down "identifier expression" so that the qualifier, template args, etc, can be distinguished between the targeted identifier.
The function can parse all of them, however the AST node compresses them all into a string.

1. Initialize identifier context
   1. Push parser scope
   2. Capture initial token as name
   3. Set scope name from token text
2. Process initial identifier component
   1. Consume identifier token
   2. Parse template arguments if present
3. Handle qualified identifiers (loop while :: found)
   1. Consume static access operator
   2. Validate token sequence:
      1. Handle destructor operator (~)
         • Validate destructor parsing context
         • Update name span if valid
         • Return invalid on context mismatch
      2. Process member function pointer (*)
         • Set possible_member_function flag if context allows
         • Return invalid if pointer unexpected
      3. Verify identifier token follows
   3. Update identifier span
      1. Extend name length to include new qualifier
      2. Consume identifier token
      3. Parse additional template arguments
4. Return completed identifier token

Technical notes:

• Current implementation treats identifier as single token span
• TODO: Refactor to AST-based identifier representation for:
  • Distinct qualifier/symbol tracking
  • Improved semantic analysis capabilities
  • Better support for nested symbol resolution

parse_include

1. Consume include directive
2. Consume the path

parse_operator_after_ret_type

This is needed as a operator defintion is not easily resolvable early on, as such this function handles resolving a operator after its been made ceratin that the type of declaration or definition is indeed for a operator signature.

By the point this function is called the following are known : export module flag, attributes, specifiers, and return type

1. Initialize operator context
   1. Push scope
   2. Parse qualified namespace identifier
   3. Consume operator keyword
2. Operator identification
   1. Validate operator token presence
   2. Set scope name from operator token
   3. Map operator token to internal operator enum:
      • Arithmetic: +, -, *, /, %
      • Assignment: +=, -=, *=, /=, %=, =
      • Bitwise: &, |, ^, ~, >>
      • Logical: &&, ||, !, ==
      • Comparison: <, >, <=, >=
      • Member access: ->, ->*
      • Special: (), [], new, delete
   4. Handle array variants for new/delete
3. Parameter and specifier processing
   1. Parse parameter list
   2. Handle multiply/member-pointer ambiguity
   3. Collect trailing specifiers
   4. Merge with existing specifiers
4. Function body handling
   1. Parse implementation if present
   2. Otherwise consume statement terminator
   3. Capture inline comments
5. Result construction
   1. Create operator node with:
      • Operator type
      • Namespace qualification
      • Parameters
      • Return type
      • Implementation body
      • Specifiers
      • Attributes
      • Module flags
   2. Attach inline comments
6. Pop scope

parse_operator_function_or_variable

When this function is called, attribute and specifiers may have been resolved, however what comes next can still be either an operator, function, or varaible.

1. Check for preprocessor macro, if there is one : parse_simple_preprocess
2. parse_type (Does the bulk of the work)
3. Begin lookahead to see if we get qualifiers or we eventually find the operator declaration
4. If we find an operator keyword : parse_operator_after_ret_type
5. otherwise :
   1. parse_identifier
   2. If we se a opening parenthesis (capture start), its a function : parse_function_after_name
   3. Its a variable : parse_variable_after_name

parse_pragma

1. Consume pragma directive
2. Process the token content into cached string

parse_params

1. Consume either a ( or < based on use_template_capture arg
2. If the we immdiately find a closing token, consume it and finish.
3. If we encounter a varadic argument, consume it and return a param_varadic ast constant
4. parse_type
5. If we have a macro, parse it (Unreal has macros as tags to parameters and or as entire arguments).
6. So long as next token isn't a comma a. If we have an identifier
   1. Consume it
   2. Check for assignment: a. Consume assign operator b. Parse the expression
7. While we continue to encounter commas a. Consume them b. Repeat steps 3 to 6.2.b
8. Consume the closing token

parse_preprocess_cond

1. Parse conditional directive
2. Process directive's content expression

parse_simple_preprocess

There is still decent room for improvement in this setup. Right now the entire macro's relevant tokens are shoved into an untyped AST. It would be better to store it instead in an AST_Macro node instead down the line.

1. Consume the macro token
2. Check for an opening curly brace
   1. Consume opening curly brace
   2. Until the closing curly is encountered consume all tokens.
   3. If the parent context is a typedef
      1. Check for end stement
         1. Consume it
         2. Consume potential inline comment
3. Otherwise do steps 3 to 3.1.2
4. Shove it all in an untyped string

parse_static_assert

1. Consume static assert and opening curly brace
2. Consume all tokens until the the closing brace is reached.
3. Consume curly brace and end statement
4. Place all tokens within braces into a content for the assert.

parse_template_args

This will get changed heavily once we have better support for typename expressions

1. Consume opening angle bracket
2. Consume all tokens until closing angle bracket
3. Consme closing angle bracket
4. Return the currtok with the ammended length.

parse_variable_after_name

This is needed as a variable defintion is not easily resolvable early on, it takes a long evaluation period before its known that the declaration or definition is a variable. As such this function handles resolving a variable.

By the point this function is called the following are known : export module flag, attributes, specifiers, value type, name

1. If its an assignment, parse the assignment expression (currently to an untyped string)
2. If its an opening curly brace, parse the expression within (currnelty to an untyped stirng).
   1. Consume the closing curly brace
3. If its a :, we're dealing with bitfield definition:
   1. Consume the assign classifier
   2. Consume the expression (currently to an untyped string)
4. If a comma is encountered : parse_variable declaration_list
5. Consume statement end
6. Check for inline comment

parse_variable_declaration_list

1. Consume the comma
2. Parse specifiers
3. parse_variable_after_name

parse_class

1. parse_class_struct

parse_constructor

This currently doesn't support postfix specifiers (planning to in the future)

1. parse_identifier
2. parse_parameters
3. If currtok is a :
   1. Consume :
   2. Parse the initializer list
   3. parse_function_body
4. If currtok is an opening curly brace
   1. parse_function_body
5. Otherwise:
   1. Consume statement end
   2. Check for inline comment

parse_destructor

1. Check for and consume virtual specifier
2. Check for the ~ operator
3. parse_identifier
4. Consume opening and closing parenthesis
5. Check for assignment operator:
   1. Consume assignment op
   2. Consume pure specifier 0
6. If not pure virtual & currtok is opening curly brace:
   1. parse_function_body
7. Otherwise:
   1. Consume end statement
   2. If currtok is comment : parse_comment

parse_enum

1. Consume enum token
2. Check for and consume class token
3. parse_attributes
4. If there is an identifier consume it
5. Check for a :
   1. Consume :
   2. parse_type
6. If there is a body parse it (Consume {):
   1. Newline : ast constant
   2. Comment : parse_comment
   3. Preprocess_Define : parse_define
   4. Preprocess_Conditional (if, ifdef, ifndef, elif ) : parse_preprocess_cond
   5. Preprocess_Else : ast constant
   6. Preprocess_Endif : ast constant
   7. Preprocess_Macro : parse_simple_preprocess
   8. Preprocess_Pragma : parse_pragma
   9. Preprocess_Unsupported : parse_smple_preprocess
   10. An actual enum entry
       1. Consume identifier
       2. If there is an assignment operator:
          1. Consume operator
          2. Consume the expression (assigned to untyped string for now)
          3. If a macro is encountered consume it (Unreal UMETA macro support)
       3. If there is a comma, consume it

parse_export_body

1. parse_global_nspace

parse_extern_link_body

1. parse_global_nspace

parse_extern_link

1. Consume Decl_Extern_Linkage
2. Consume the linkage identifier
3. parse_extern_link_body

parse_friend

1. Consume friend
2. parse_type
3. If the currok is an identifier its a function declaration or definition
   1. parse_function_after_name
4. Consume end statement so long as its not a function definion
5. Check for inline comment, parse_comment if exists

parse_function

1. Check and parse for export
2. parse_attributes
3. Parse specifiers
4. parse_type
5. parse_identifier
6. parse_function_after_name

parse_namespace

1. Consume namespace declaration
2. Parse identifier
3. parse_global_namespace

parse_operator

1. Check for and parse export declaration
2. parse_attributes
3. Parse specifiers
4. parse_type
5. parse_operator_after_ret_type

parse_operator_cast

1. Look for and parse a qualifier namespace for the cast (in-case this is defined outside the class's scope)
2. Consume operator declaration
3. parse_type
4. Consume opening and closing parethesis
5. Check for a const qualifiying specifier
6. Check to see if this is a definition ({)
   1. Consume {
   2. Parse body to untyped string (parsing statement and expressions not supported yet)
   3. Consume }
7. Otherwise:
   1. Consume end statement
   2. Check for and consume comment : parse_comment

parse_struct

1. parse_class_struct

parse_template

Note: This currently doesn't support templated operator casts (going to need to add support for it)

1. Check for and parse export declaration
2. Consume template declaration
3. parse_params
4. Parse for any of the following:
   1. Decl_Class : parse_class
   2. Decl_Struct : parse_struct
   3. Decl_Union : parse_union
   4. Decl_Using : parse_using
   5. The following compound into a resolved definition or declaration:
      1. parse_attributes
      2. Parse specifiers
      3. Attempt to parse as constructor or destructor: parse_global_nspace_constructor_destructor
      4. Otherwise: parse_operator_function_or_variable

parse_type

This function's implementation is awful and not done correctly. It will most likely be overhauled in the future as I plan to segement the AST_Type into several AST varaints along with sub-types to help produce robust type expressions.
Hopefully I won't need to make authentic type expressions as I was hopeing to avoid that...

Current Algorithim

Anything that is in the qualifier capture of the function typename is treated as an expression abstracted as an untyped string

1. parse_attributes
2. Parse specifiers
3. If the parse_type was called from a template parse, check to see if class was used instead of typname and consume as name.
4. This is where things get ugly for each of these depend on what the next token is.
   1. If its an in-place definition of a class, enum, struct, or union:
   2. If its a decltype (Not supported yet but draft impl there)
   3. If its a compound native type expression (unsigned, char, short, long, int, float, dobule, etc )
   4. Ends up being a regular type alias of an identifier
5. Parse specifiers (postfix)
6. We need to now look ahead to see If we're dealing with a function typename
7. If wer're dealing with a function typename:
   1. Shove the specifiers, and identifier code we have so far into a return type typename's Name (untyped string)
      1. Reset the specifiers code for the top-level typeanme
   2. Check to see if the next token is an identifier:
      1. parse_identifier
   3. Check to see if the next token is capture start and is not the last capture ("qualifier capture"):
      1. Consume (
      2. Consume expresssion between capture
      3. Consume )
   4. parse_params
   5. Parse postfix specifiers
8. Check for varaidic argument (param pack) token:
   1. Consume varadic argument token

WIP - Alternative Algorithim

Currently wrapped up via macro: GEN_USE_NEW_TYPENAME_PARSING Anything that is in the qualifier capture of the function typename is treated as an expression abstracted as an untyped string

1. parse_attributes
2. Parse specifiers (prefix)
3. This is where things get ugly for each of these depend on what the next token is.
   1. If its an in-place definition of a class, enum, struct, or union:
   2. If its a decltype (Not supported yet but draft impl there)
   3. If its a compound native type expression (unsigned, char, short, long, int, float, dobule, etc )
   4. Ends up being a regular type alias of an identifier
4. Parse specifiers (postfix)
   1. If any specifiers are found populate specifiers code with them.
5. We need to now look ahead to see If we're dealing with a function typename
6. If wer're dealing with a function typename:
   1. Shove the specifiers, and identifier code we have so far into a return type typename's Name (untyped string)
      1. Reset the specifiers code for the top-level typename
   2. Check to see if the next token is an identifier:
      1. parse_identifier
   3. Check to see if the next token is capture start and is not the last capture ("qualifier capture"):
      1. Consume (
      2. Parse binding specifiers
      3. parse_identifier
      4. parse_parameters -> params_nested
      5. Consume )
      6. Construct a nested function typename definition for the qualifier Name
   4. parse_params - > params
   5. Parse postfix specifiers
7. Check for varaidic argument (param pack) token:
   1. Consume varadic argument token

Later: Algorithim based on typename expressions

parse_typedef

1. Check for export module specifier
2. typedef keyword
3. If its a preprocess macro: Get the macro name
4. Else:
   1. Check to see if its a complicated definition (in-place enum, class, struct, union)
   2. If its a complicated definition:
      1. Perform the look ahead similar to parse_complicated_definition's implementation
      2. Check to see if its a forward declaration : parse_forward_declaration
      3. If end[-1] is an identifier:
         1. Its either an in-place, varaible type qualified identifier, or indirection type:
            1. parse_foward_or_definition
      4. else if end[-1] is a closing curly brace
         1. Its a definition: parse_forward_or_definition
      5. else if end[-1] is a closing square brace 2. Its an array definition: parse_type
   3. Else : parse-type
   4. Check for identifier : Consume the token
   5. parse_array_decl
5. Consume end statement
6. Check for inline comment : parse_comment

parse_union

1. Check for export module specifier
2. union keyword
3. parse_attributes
4. Check for identifier
5. Parse the body (Possible options):
   1. Newline
   2. Comment
   3. Decl_Class
   4. Decl_Enum
   5. Decl_Struct
   6. Decl_Union
   7. Preprocess_Define
   8. Preprocess_Conditional (if, ifdef, ifndef, elif, else, endif)
   9. Preprocess_Macro
   10. Preprocess_Pragma
   11. Unsupported preprocess directive
   12. Variable
6. If its not an inplace definiton: End Statement

parse_using

1. Check for export module specifier
2. using keyword
3. Check to see if its a using namespace
4. Get the identifier
5. If its a regular using declaration:
   1. parse_attributes
   2. parse_type
   3. parse_array_decl
6. End statement
7. Check for inline comment

parse_variable

1. Check for export module specifier
2. parse_attributes
3. parse specifiers
4. parse_type
5. parse_identifier
6. parse_variable_after_name