C++ Flex Bison Cmake, yylex was not declared in this scope

Question

I am having trouble using cmake, flex and bison together.

• File Structure

.
├── build
│   ├── (excluded cmake files)
├── CMakeLists.txt
├── lexer
│   ├── lexer.c
│   └── lexer.l
├── parser
│   └── parser.y
├── src
│   ├── location.hh
│   ├── parser.cpp
│   ├── parser.hpp
│   ├── position.hh
│   ├── reqLangMain.cpp
│   └── stack.hh

• CMakeLists.txt

cmake_minimum_required(VERSION 3.13.4)
project(req_lang)

find_package(BISON)
find_package(FLEX)

BISON_TARGET(reqParser 
    ${CMAKE_SOURCE_DIR}/parser/parser.y 
    ${CMAKE_SOURCE_DIR}/src/parser.cpp
        #COMPILE_FLAGS "-L C++"
)
FLEX_TARGET(reqLexer 
    ${CMAKE_SOURCE_DIR}/lexer/lexer.l 
    ${CMAKE_SOURCE_DIR}/lexer/lexer.c
        #COMPILE_FLAGS  "--bison-bridge" #"-+"
)

ADD_FLEX_BISON_DEPENDENCY(reqLexer reqParser)
include_directories(${CMAKE_CURRENT_BINARY_DIR})
set(SOURCES
    ${PROJECT_SOURCE_DIR}/src/reqLangMain.cpp
)
add_executable(${PROJECT_NAME} 
    ${SOURCES}
    ${BISON_reqParser_OUTPUTS}
    ${FLEX_reqLexer_OUTPUTS}
)
target_link_libraries(${PROJECT_NAME}
    ${FLEX_LIBRARIES}
)

• lexer.l

%option noyywrap
%{
    #include <stdio.h>
    #include "../src/parser.hpp"
%}

%%
[[:digit:]]+  { yylval->num = atoi(yytext);   return NUMBER;}
[[:alnum:]]+  { yylval->str = strdup(yytext); return STRING;}
"="|";"       { return yytext[0];}
.  {}
%%

• paser.y

%{
#define YYPARSE_PARAM lexer
#define YYLEX_PARAM   lexer

#include <stdio.h>
#include <stdlib.h>
%}

%union {
    int num;
    char* str;
}

%token <str> STRING
%token <num> NUMBER

%%
assignment:
    STRING '=' NUMBER ';' {
        printf( "(setf %s %d)", $1, $3 );
    }
;
%%

Ultimately, I keep getting (some combination of) yylex, and yyerror were not declared in this scope when I run cd ..; cmake -S . -B build; cd build/; make; from the build directory.

As for what I've attempted: researched git repos with similar tags, browsed stack-overflow for similar issues, gone though flex/cmake documentation, toggling flex and bison flags -+ and --bison_bridge.

The goal is a bison produced cpp file.

I apologize in advance if this post was lengthy or if the issue is a one-line resolution.