Get the GC to work again and change the allocator

Allocator subsystem works with a single contiguous chunk of memory.
Small object allocator uses fixed-size bins and never attempts to merge chunks,
and the large object allocator is a slightly-modified version of the SQLite
mem3.c allocator.
The GC uses the boundaries of this chunk of memory, plus a table of
flags, to determine if a Value refers to a heap allocation or not (we no longer have type information per-Value). The
current implementation requires storing the size of each heap object in
the GC header, but it should be possible to elide this requirement using flags (using 2 bits for each flag instead of 1, see golang GC implementation).
Should support expanding the heap via. sbrk or similar (will require
changing paw_Alloc to expand/contract the dynamic memory area, rather
than implement a realloc-like interface).

CMakeLists.txt

@@ -31,31 +31,25 @@ else()
             INTERFACE m)
 endif()
 
-include(FetchContent)
-FetchContent_Declare(gc
-    GIT_REPOSITORY https://github.com/ivmai/bdwgc.git
-    GIT_TAG v8.2.6)
-FetchContent_MakeAvailable(gc)
-
 set(PAW_SOURCE_DIR ${PROJECT_SOURCE_DIR}/src)
 
 add_library(paw STATIC)
 target_sources(paw
-    PUBLIC  ${PAW_SOURCE_DIR}/api.h
+    PUBLIC  ${PAW_SOURCE_DIR}/alloc.h
+            ${PAW_SOURCE_DIR}/api.h
             ${PAW_SOURCE_DIR}/ast.h
             ${PAW_SOURCE_DIR}/auxlib.h
             ${PAW_SOURCE_DIR}/call.h
             ${PAW_SOURCE_DIR}/code.h
             ${PAW_SOURCE_DIR}/compile.h
             ${PAW_SOURCE_DIR}/debug.h
             ${PAW_SOURCE_DIR}/env.h
-            ${PAW_SOURCE_DIR}/gc_aux.h
+            ${PAW_SOURCE_DIR}/gc.h
             ${PAW_SOURCE_DIR}/hir.h
             ${PAW_SOURCE_DIR}/lex.h
             ${PAW_SOURCE_DIR}/lib.h
             ${PAW_SOURCE_DIR}/map.h
             ${PAW_SOURCE_DIR}/mem.h
-            ${PAW_SOURCE_DIR}/meta.h
             ${PAW_SOURCE_DIR}/opcode.h
             ${PAW_SOURCE_DIR}/os.h
             ${PAW_SOURCE_DIR}/parse.h
@@ -67,38 +61,35 @@ target_sources(paw
             ${PAW_SOURCE_DIR}/unify.h
             ${PAW_SOURCE_DIR}/util.h
             ${PAW_SOURCE_DIR}/value.h
-    PRIVATE ${PAW_SOURCE_DIR}/api.c
+    PRIVATE ${PAW_SOURCE_DIR}/alloc.c
+            ${PAW_SOURCE_DIR}/api.c
             ${PAW_SOURCE_DIR}/ast.c
             ${PAW_SOURCE_DIR}/auxlib.c
             ${PAW_SOURCE_DIR}/call.c
-            ${PAW_SOURCE_DIR}/check.c
             ${PAW_SOURCE_DIR}/code.c
             ${PAW_SOURCE_DIR}/codegen.c
             ${PAW_SOURCE_DIR}/compile.c
             ${PAW_SOURCE_DIR}/debug.c
             ${PAW_SOURCE_DIR}/env.c
-            ${PAW_SOURCE_DIR}/gc_aux.c
+            ${PAW_SOURCE_DIR}/gc.c
             ${PAW_SOURCE_DIR}/hir.c
             #${PAW_SOURCE_DIR}/iolib.c
             ${PAW_SOURCE_DIR}/lex.c
             ${PAW_SOURCE_DIR}/lib.c
             #${PAW_SOURCE_DIR}/mathlib.c
             ${PAW_SOURCE_DIR}/map.c
             ${PAW_SOURCE_DIR}/mem.c
-            ${PAW_SOURCE_DIR}/meta.c
             ${PAW_SOURCE_DIR}/opcode.c
             ${PAW_SOURCE_DIR}/os.c
             ${PAW_SOURCE_DIR}/parse.c
+            ${PAW_SOURCE_DIR}/resolve.c
             ${PAW_SOURCE_DIR}/rt.c
             ${PAW_SOURCE_DIR}/str.c
             ${PAW_SOURCE_DIR}/type.c
             ${PAW_SOURCE_DIR}/unify.c
             ${PAW_SOURCE_DIR}/util.c
             ${PAW_SOURCE_DIR}/value.c
             ${PAW_SOURCE_DIR}/vector.c)
-target_link_libraries(paw
-    PRIVATE paw_context 
-    PUBLIC gc)
 target_include_directories(paw
     PUBLIC ${PAW_SOURCE_DIR})
 target_compile_definitions(paw

GRAMMER.md

@@ -1,7 +1,7 @@
 # Paw language grammer (EBNF)
 **TODO: get rid of requirement that "break" | "return" | "continue" is the last statement in the block**
 **      just don't emit unreachable code**
-**      use a tool to validate this...**
+**      use a tool to validate this EBNF...**
 
 ## Module
 ```ebnf

README.md

@@ -324,13 +324,14 @@ assert(status != 0)
 + [x] type inference for `struct` templates and builtin containers
 + [x] sum types/discriminated unions (`enum`)
 + [x] product types (tuple)
++ [ ] refactor user-provided allocation interface to allow heap expansion
 + [ ] module system and `import` keyword
 + [ ] methods using `impl` blocks
 + [ ] error handling
 + [ ] type inference for `enum` templates
 + [ ] pattern matching (`switch` construct)
 + [ ] pattern matching (`if let`, `let` bindings)
-+ [ ] custom garbage collector (using Boehm GC for now)
++ [x] custom garbage collector (using Boehm GC for now)
 + [ ] split off UTF-8 stuff into `String` structure, where `str` is a byte array and `String` is always valid UTF-8
 + [ ] constness (`var` vs `let`)
 + [ ] compiler optimization passes