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Read the header instead of trusting the transcription

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declare-c generates the wrapper, the typedefs and the prototype from one
declaration, so they cannot disagree with each other. What nothing checked was
whether the declaration matched the library — BUILT.md records that as trusted
rather than guaranteed, because no header was ever read.

This reads one. clang is asked for a JSON AST dump of the header and shelled
out to, not linked: -Xclang -ast-dump=json is the same binary on PATH that
every build already runs, which is plan.org's "Why LLVM IR as text" applied a
second time. Zig's old @cImport linked clang as a library and that is precisely
the dependency plan.org rejected.

cjson.ml is enough JSON to read the dump and no more, so this adds no opam
package to parse it.

What comes out of the header is signatures and nothing else — not structs, not
enums, not macros. The bound on how much is imported is the package's own
defstructs: a function whose signature mentions a struct the package has not
described is refused with that reason, so vendor/raylib describing thirteen
structs is what makes the import thirteen structs wide. Keeping the layouts
hand-written is also what makes checking them against the header's records
worth doing — a _Static_assert was rejected in BUILT.md as circular, and this
is not, because the two sides have different authors.

Refusals are demotions, taken from Zig's translator: it never drops a
declaration it cannot handle, it binds the name to a @compileError carrying the
reason so the failure lands at the use site. Load.refuse_hidden is already that
mechanism. So a returned char * does not kill the header — it makes one name
unavailable, with the reason attached.

flan import-c prints what it would produce, what it refused, how the package's
defstructs compare with the header's records, and how the hand-written
declare-c lines compare with the header's signatures.

Against raylib 5.5, the version whose .so vendor/raylib/link names: all 16
defstructs and all 172 hand-written declare-c agree exactly. Against the 5.1-dev
header installed in /usr/local it reports ten differences, nine functions that
version does not have and one that gained a parameter — so the check has teeth
and the clean run is not a vacuous one.
This commit is contained in:
Joseph Ferano 2026-09-12 15:15:01 +07:00
parent cd0f0a486e
commit 19aa10158a
3 changed files with 1019 additions and 0 deletions
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98
bin/main.ml
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@ -148,6 +148,103 @@ let () =
| [] -> Printf.printf "%s: no declare-c, so no generated C\n" path
| parts -> List.iter (fun (_, src) -> print_string src) parts))
files
(* A header, read. The importer is a pure function of the header and the
package beside it, so it can be looked at without building anything —
which is what makes the diff against a hand-written binding possible, and
what makes "generate once and commit the result" a usable option rather
than a description of one. Prints the declarations it would produce, then
what it refused and why, then how the package's defstructs compare with
the header's records. *)
| _ :: "import-c" :: header :: rest ->
with_errors header (fun () ->
let pkg = List.filter (fun a -> Filename.check_suffix a ".flan") rest in
let flags =
List.filter (fun a -> not (Filename.check_suffix a ".flan")) rest
in
let ds =
List.concat_map
(fun f -> Flan.Parse.program (Flan.Reader.read_file f)) pkg
in
let structs =
List.filter_map
(fun (d : Flan.Ast.decl) ->
match d.Flan.Ast.d with
| Flan.Ast.Defstruct (n, fs) -> Some (n, fs)
| _ -> None)
ds
in
let known_enums =
List.filter_map
(fun (d : Flan.Ast.decl) ->
match d.Flan.Ast.d with
| Flan.Ast.Defenum (n, _) -> Some n
| _ -> None)
ds
in
let taken = Hashtbl.create 64 in
List.iter
(fun d ->
match Flan.Ast.declared_name d with
| Some n -> Hashtbl.replace taken n ()
| None -> ())
ds;
let bound_syms =
List.filter_map
(fun (d : Flan.Ast.decl) ->
match d.Flan.Ast.d with
| Flan.Ast.Declare (_, s) | Flan.Ast.DeclareC (_, s) -> Some s
| _ -> None)
ds
in
let imported, dump, env =
Flan.Cimport.header ~loc:(Flan.Loc.make header 0 0) ~header ~flags
~known_structs:(List.map fst structs) ~known_enums ~taken ~bound_syms
in
List.iter
(fun d -> print_endline (Flan.Cimport.decl_source d))
imported.Flan.Cimport.decls;
Printf.printf "\n;; %d imported, %d refused, of %d functions in %s\n"
(List.length imported.Flan.Cimport.decls)
(List.length imported.Flan.Cimport.hidden)
(List.length dump.Flan.Cimport.fns) header;
List.iter
(fun (n, why) -> Printf.printf ";; refused %s: %s\n" n why)
imported.Flan.Cimport.hidden;
(match Flan.Cimport.check_structs ~env ~structs dump with
| [] ->
if structs <> [] then
Printf.printf ";; every defstruct agrees with the header\n"
| bad ->
List.iter
(fun (n, why) -> Printf.printf ";; DISAGREES %s: %s\n" n why)
bad);
(* And the bindings the package already wrote by hand, against the
header's own signatures. Nothing else in the build can do this: a
wrong declare-c is wrong in the generated prototype too, so the two
agree with each other and only the library disagrees. *)
let bound =
List.filter_map
(fun (d : Flan.Ast.decl) ->
match d.Flan.Ast.d with
| Flan.Ast.DeclareC (fn, sym) -> Some (fn, sym)
| _ -> None)
ds
in
if bound <> [] then
match Flan.Cimport.diff_bound ~env ~bound dump with
| [] ->
Printf.printf
";; all %d hand-written declare-c agree with the header\n"
(List.length bound)
| ds ->
Printf.printf ";; %d of %d hand-written declare-c disagree\n"
(List.length ds) (List.length bound);
List.iter
(fun (x : Flan.Cimport.sig_diff) ->
Printf.printf ";; DIFFERS %s (%s): %s\n"
x.Flan.Cimport.dflan x.Flan.Cimport.dsym x.Flan.Cimport.dwhy)
ds)
(* The IR is target-independent — [Emit] writes no triple and no datalayout,
which is what lets one .ll serve both targets — so there is nothing for a
target to change here. Refused rather than accepted and ignored: silently
@ -289,6 +386,7 @@ let () =
| _ ->
prerr_endline
"usage: flan (read|parse|check|emit|shim) <file.flan>...\n\
\ flan import-c <header.h> [package.flan...] [clang flags...]\n\
\ flan build <file.flan> [-o out] [--no-bounds-checks] [--dev] \
[--debug] [--sanitize] [--target=wasm32-wasi|web]\n\
\ flan run <file.flan> [args...]\n\

747
lib/cimport.ml Normal file
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@ -0,0 +1,747 @@
(** Reading a C header, so a binding is checked against the library instead of
transcribed from it.
[declare-c] closed half the gap: the wrapper, the typedefs and the
prototype are generated, so they cannot disagree with each other. The half
it left open is the one BUILT.md records as *trusted* — that the signature
somebody typed is the function's real signature. Nothing checked it,
because no header was ever read. This reads one.
{2 Why clang, and why not linked to it}
Zig's old [@cImport] ran clang as a *library*. That is precisely the
dependency plan.org rejected when it chose text IR over libLLVM bindings: a
version-pinned C++ library breaks routinely on upgrade, a binary on PATH
does not. So this shells out for [clang -Xclang -ast-dump=json
-fsyntax-only], which is the same binary the build already runs for every
other purpose and adds no dependency that is not already being paid for.
(Zig has since replaced clang here altogether with Aro, a C frontend
written in Zig. Their reason was to ship a compiler containing no clang at
all, self-contained and cross-compiling anywhere. This project has the
opposite premise — [clang] on PATH is the whole toolchain assumption — so
that move is explained by a constraint that does not apply here.)
{2 What is imported, and what bounds it}
Functions, and only functions. Not structs, not enums, not macros.
The bound on how much gets imported is not a curated list — it is the
package's own [defstruct]s. A C function is imported when every type in its
signature maps to something the package already declares or to a machine
scalar; a function mentioning a struct the package has not described is
refused, by name, with that reason. So [vendor/raylib] describing thirteen
structs is what makes the import thirteen structs wide, and describing a
fourteenth is what widens it. The layouts stay hand-written and stay the
single statement about what raylib's structs are, which is the thing the
acceptance tests pin; only the *signatures* come from the header.
This is also why no [defstruct] is generated. Generating one would make the
header the authority on layout, and then the check below — comparing the
package's [defstruct]s against the header's records — would be comparing
the header with itself. Keeping the layouts hand-written is what makes
[check_structs] an independent second source, and that check is the
cheapest real closure of BUILT.md's trusted-not-guaranteed gap: a
[_Static_assert] was rejected there as circular for exactly this reason,
and this is not circular, because the two sides have different authors.
{2 Refusing by demotion}
Taken from Zig, and the one decision here most worth keeping. Zig's
translator never drops a declaration it cannot handle: [failDecl] emits the
name bound to a [@compileError] carrying the reason, so the name still
exists, the program still compiles, and asking for that one name fails —
at the use site, with the reason. A wholesale import has hundreds of
refusals and a caller cares about the one they typed.
Flan has that mechanism already: [Load.refuse_hidden] is the same idea,
built for [main]. So a refused import becomes a hidden name.
[rl/get-gamepad-name] is not a name, and a program that writes it is told
*why* — "returns const char *, and a string only crosses as a parameter" —
rather than "unknown name".
This is also the split the existing generator needs and does not have.
[Shim] refuses through [Loc.fail], which is right when a human named one
function and wrong for a wholesale import: one returned [const char *]
would otherwise kill the whole header. Same judgement, different
disposition — a hand-written [declare-c] still hard-fails, and [Shim] is
untouched. *)
let fail = Loc.fail
(* ── Names ─────────────────────────────────────────────────────────
The C symbol is kept verbatim in [Ast.DeclareC], so the kebab rule never
needs an inverse: the generated wrapper reads the spelling out of the
declaration rather than reconstructing it. What the rule does have to be is
*injective over one header*, since two C functions arriving under one Flan
name is a collision the checker would report as a duplicate declaration
about a name nobody wrote. That is asserted below, by name.
The rule, in full. A boundary goes before a character that is
- an uppercase letter after a lowercase one — [InitWindow] → init-window
- an uppercase letter between an uppercase and
a lowercase one — [ColorToHSV] → color-to-hsv
- a digit after a lowercase letter — [BeginMode2D] → begin-mode-2d
and nowhere else; an underscore is a boundary and disappears. The third
clause is what keeps [2D] together as one word, and the second is what keeps
an acronym together: [SetTargetFPS] is set-target-fps and not
set-target-f-p-s, [UnloadUTF8] is unload-utf8. *)
let kebab (s : string) : string =
let n = String.length s in
let b = Buffer.create (n + 8) in
String.iteri
(fun i c ->
let prev = if i > 0 then s.[i - 1] else '\000' in
let next = if i + 1 < n then s.[i + 1] else '\000' in
let upper c = c >= 'A' && c <= 'Z' in
let lower c = c >= 'a' && c <= 'z' in
let digit c = c >= '0' && c <= '9' in
if
i > 0 && prev <> '_'
&& ((upper c && lower prev)
|| (upper c && upper prev && lower next)
|| (digit c && lower prev))
then Buffer.add_char b '-';
if c = '_' then (if Buffer.length b > 0 then Buffer.add_char b '-')
else Buffer.add_char b (Char.lowercase_ascii c))
s;
Buffer.contents b
(* ── What clang was asked, and what it said ────────────────────────── *)
(* One C function, as the dump describes it and before anything is decided
about whether Flan can hold it. *)
type cfn = {
csym : string;
cret : string; (* the return type, as clang spells it *)
cparams : (string * string) list; (* name (possibly ""), type *)
cvariadic : bool;
cloc : Loc.t; (* the line of the header it is on *)
}
(* One C struct, for checking a [defstruct] against. *)
type crecord = { rname : string; rfields : (string * string) list }
type dump = {
fns : cfn list;
records : crecord list;
(* A typedef's underlying spelling: [Texture2D] → [struct Texture], and
[Camera] → [Camera3D]. Followed when the spelled name is not one the
package declares, which is what lets a Flan [defstruct Texture2D] serve a
C parameter typed [Texture]. *)
typedefs : (string * string) list;
(* The typedef names that are enums rather than records. A C enum is an int
on every target this compiles for, which is also what [Shim] lowers a Flan
[defenum] to, so the two agree by construction. *)
enums : string list;
}
let clang_argv ~header ~flags =
[ "clang"; "-Xclang"; "-ast-dump=json"; "-fsyntax-only" ] @ flags @ [ header ]
(* clang's stdout, or its stderr if it failed. Run through [Unix.create_process]
rather than a shell so a path with a space in it needs no quoting and no
[Filename.quote] round trip. *)
let run_clang ~loc ~header ~flags =
if not (Sys.file_exists header) then
fail loc "no such header: %s" header;
let argv = clang_argv ~header ~flags in
let out_r, out_w = Unix.pipe ~cloexec:false () in
let err_r, err_w = Unix.pipe ~cloexec:false () in
let pid =
try
Unix.create_process "clang" (Array.of_list argv) Unix.stdin out_w err_w
with Unix.Unix_error _ ->
List.iter Unix.close [ out_r; out_w; err_r; err_w ];
fail loc
"clang is not on PATH, and reading a C header is done by running it \
(%s)"
(String.concat " " argv)
in
Unix.close out_w;
Unix.close err_w;
(* Both pipes have to be drained as they fill: the dump is megabytes and a
process blocked writing stdout while this waits on its exit is a deadlock
that only shows up on a big header. *)
let read_all fd =
let b = Buffer.create 65536 in
let chunk = Bytes.create 65536 in
let rec go () =
match Unix.read fd chunk 0 65536 with
| 0 -> ()
| k -> Buffer.add_subbytes b chunk 0 k; go ()
| exception Unix.Unix_error (Unix.EINTR, _, _) -> go ()
in
go (); Buffer.contents b
in
let out_buf = Buffer.create (1 lsl 21) in
let err_buf = Buffer.create 4096 in
(* Read stdout first but keep stderr drained too. clang writes very little to
stderr for a header that parses, and a header that does not parse writes
little enough to fit a pipe, so alternating is not needed — but stdout is
the one that is megabytes, so it is the one read in the loop. *)
Buffer.add_string out_buf (read_all out_r);
Buffer.add_string err_buf (read_all err_r);
Unix.close out_r;
Unix.close err_r;
let status = snd (Unix.waitpid [] pid) in
(match status with
| Unix.WEXITED 0 -> ()
| _ ->
fail loc "clang could not parse %s:\n%s" header
(String.trim (Buffer.contents err_buf)));
Buffer.contents out_buf
(* ── Reading the dump ──────────────────────────────────────────────── *)
(* clang omits [loc.file] when it is the same as the previous node's, so file
attribution is a fold over the children in order and not a lookup. Getting
this wrong is not loud: it silently imports everything the header includes,
or nothing at all. *)
let qual j = match Cjson.mem "type" j with Some t -> Cjson.str "qualType" t | None -> None
let read_dump ~header (root : Cjson.t) : dump =
let want = try Unix.realpath header with Unix.Unix_error _ -> header in
let same f = try Unix.realpath f = want with Unix.Unix_error _ -> f = want in
let cur = ref "" in
let fns = ref [] and records = ref [] and typedefs = ref [] and enums = ref [] in
List.iter
(fun d ->
(match Cjson.mem "loc" d with
| Some l -> (match Cjson.str "file" l with Some f -> cur := f | None -> ())
| None -> ());
let mine = same !cur in
let name = Cjson.str "name" d in
match (Cjson.str "kind" d, name) with
| Some "FunctionDecl", Some nm when mine ->
(* A [static] or [inline] definition in a header has no symbol to
link against from outside the translation unit that has the body.
Left out rather than imported and met at the linker. *)
let sc = Cjson.str "storageClass" d in
if sc <> Some "static" then begin
let q = match qual d with Some q -> q | None -> "" in
let cret =
match String.index_opt q '(' with
| Some k -> String.trim (String.sub q 0 k)
| None -> q
in
let cparams =
List.filter_map
(fun p ->
if Cjson.str "kind" p = Some "ParmVarDecl" then
Some (Option.value ~default:"" (Cjson.str "name" p),
Option.value ~default:"" (qual p))
else None)
(Cjson.arr "inner" d)
in
let line =
match Cjson.mem "loc" d with
| Some l ->
(match Cjson.mem "line" l with
| Some (Cjson.Num f) -> int_of_float f
| _ -> 0)
| None -> 0
in
fns := { csym = nm; cret; cparams; cvariadic = Cjson.bool "variadic" d;
cloc = Loc.make !cur line 1 }
:: !fns
end
| Some "RecordDecl", Some nm when mine && Cjson.bool "completeDefinition" d ->
let rfields =
List.filter_map
(fun f ->
if Cjson.str "kind" f = Some "FieldDecl" then
Some (Option.value ~default:"" (Cjson.str "name" f),
Option.value ~default:"" (qual f))
else None)
(Cjson.arr "inner" d)
in
(* A bitfield has no address and no Flan spelling; a record holding
one is not one this can check, so it is not recorded and the
[defstruct] beside it is left unchecked rather than checked
wrongly. Same for an unnamed field, which is an anonymous union or
struct. *)
let ok =
List.for_all
(fun f ->
Cjson.str "kind" f <> Some "FieldDecl"
|| (not (Cjson.bool "isBitfield" f)
&& Cjson.str "name" f <> None))
(Cjson.arr "inner" d)
in
if ok then records := { rname = nm; rfields } :: !records
| Some "TypedefDecl", Some nm when mine ->
(match qual d with
| Some u ->
typedefs := (nm, u) :: !typedefs;
if String.length u > 5 && String.sub u 0 5 = "enum " then
enums := nm :: !enums
| None -> ())
| _ -> ())
(Cjson.arr "inner" root);
{ fns = List.rev !fns; records = List.rev !records;
typedefs = List.rev !typedefs; enums = List.rev !enums }
(* ── C types into Flan types ───────────────────────────────────────── *)
(* What the package already says exists. The importer adds no type of its own:
it either finds a Flan name for a C type here or refuses the function. *)
type env = {
known_structs : string list; (* the package's defstruct names *)
known_enums : string list; (* its defenum names *)
d : dump;
}
exception Refused of string
let refuse fmt = Printf.ksprintf (fun m -> raise (Refused m)) fmt
let strip_prefix p s =
let lp = String.length p in
if String.length s >= lp && String.sub s 0 lp = p then
Some (String.trim (String.sub s lp (String.length s - lp)))
else None
(* [const struct Foo] → [Foo]. Qualifiers carry no Flan meaning — Flan has no
const — but they have to come off before the name is recognised, and
const-ness is read *before* this, where it still means something (see
[param_ty]). *)
let rec bare s =
let s = String.trim s in
match
List.find_map (fun p -> strip_prefix p s)
[ "const "; "volatile "; "restrict "; "struct "; "union "; "enum " ]
with
| Some s' -> bare s'
| None -> s
(* A generated type expression carries no location of its own: the thing a
message about it wants to point at is the declaration's line in the header,
which is what the field and the declaration below carry. *)
let ty t = { Ast.t; tloc = Loc.unknown }
let rec ty_source (t : Ast.texpr) =
match t.Ast.t with
| Ast.Tname n -> n
| Ast.Tapp (n, args) ->
Printf.sprintf "(%s %s)" n (String.concat " " (List.map ty_source args))
| Ast.Tslice e -> Printf.sprintf "[%s]" (ty_source e)
| Ast.Tarray (Ast.Lint n, e) -> Printf.sprintf "[%Ld %s]" n (ty_source e)
| Ast.Tarray (Ast.Lname n, e) -> Printf.sprintf "[%s %s]" n (ty_source e)
| Ast.Tmap (k, v) -> Printf.sprintf "{%s %s}" (ty_source k) (ty_source v)
| Ast.Tfn (ps, r) ->
Printf.sprintf "(Fn [%s] %s)"
(String.concat " " (List.map ty_source ps)) (ty_source r)
let tname n = ty (Ast.Tname n)
(* The machine scalars, and the ones deliberately left out.
[long], [size_t] and the rest are refused rather than guessed, and the
reason is specific to this project rather than general fussiness: it builds
for x86-64, for wasm32-wasi and for the browser, and [long] is 64 bits on
the first and 32 on the others. A guess would be right for the target that
gets tested and silently wrong for the two that do not. A header that wants
one says so in [declare-c], where a human takes responsibility for it. *)
let scalar = function
| "void" -> Some "Unit"
| "_Bool" | "bool" -> Some "bool"
| "char" | "signed char" | "int8_t" -> Some "i8"
| "unsigned char" | "uint8_t" -> Some "u8"
| "short" | "short int" | "int16_t" -> Some "i16"
| "unsigned short" | "unsigned short int" | "uint16_t" -> Some "u16"
| "int" | "signed int" | "int32_t" -> Some "i32"
| "unsigned" | "unsigned int" | "uint32_t" -> Some "u32"
| "int64_t" | "long long" | "long long int" -> Some "i64"
| "uint64_t" | "unsigned long long" | "unsigned long long int" -> Some "u64"
| "float" -> Some "f32"
| "double" -> Some "f64"
| _ -> None
let width_varies =
[ "long"; "long int"; "unsigned long"; "unsigned long int"; "size_t";
"ssize_t"; "ptrdiff_t"; "intptr_t"; "uintptr_t"; "time_t"; "wchar_t" ]
(* A named type, after qualifiers and pointers are gone: a struct the package
describes, an enum, or nothing this can hold. *)
let rec named env (n : string) : Ast.texpr =
if List.mem n env.known_structs then tname n
else if List.mem n env.known_enums then tname n
else if List.mem n env.d.enums then
(* A C enum is an int, which is what [Shim] lowers a Flan [defenum] to, so
this is the same ABI and not a widening. What it loses is the nice face:
a parameter typed [Key] takes [:space] at the call site and an [i32]
does not. That is a reason to keep a hand-written [declare-c] for the
few calls where it matters, not a reason to refuse the other five
hundred. *)
tname "i32"
else if List.mem_assoc n env.d.typedefs then begin
let u = bare (List.assoc n env.d.typedefs) in
if u = n then refuse "%s is a typedef of itself" n else named env u
end
else if List.exists (fun r -> r.rname = n) env.d.records then
refuse
"%s is a struct the package does not describe — add a defstruct for it, \
or keep a hand-written declare-c"
n
else if List.mem n width_varies then
refuse
"%s has a width that differs between this project's own targets (64 \
bits on x86-64, 32 on wasm32), so no single Flan type is right for it"
n
else refuse "%s is not a type the header importer knows" n
(* A type in any position but an outermost parameter. Pointers are where C says
least and Flan has to say something: a [T *] is one T, or an array of them,
or null, and the header does not distinguish. Flan's [(Ptr T)] claims only
"the address of a T", which is the weakest of those and therefore the only
honest one — the same judgement Zig makes when it translates [T *] to
[[*c]T] rather than to a single-item pointer. *)
and value_ty env (s : string) : Ast.texpr =
let s = String.trim s in
if String.length s > 0 && s.[String.length s - 1] = '*' then begin
let inner = String.trim (String.sub s 0 (String.length s - 1)) in
let b = bare inner in
(* [void *] is an address of unknown element type; [(Ptr u8)] is what the
package already spells that as ([Image.data]). *)
if b = "void" then ty (Ast.Tapp ("Ptr", [ tname "u8" ]))
else ty (Ast.Tapp ("Ptr", [ value_ty env inner ]))
end
else if String.contains s '[' then
refuse "%s is an array, which C passes as a pointer and Flan as a value" s
else if String.contains s '(' then
refuse "%s is a function pointer, and a C callback is not implemented" s
else
let b = bare s in
match scalar b with
| Some "Unit" -> refuse "void is not a value"
| Some p -> tname p
| None -> named env b
(* A parameter, where two C spellings mean things no other position does.
[const char *] is a string going in, and [Shim] already knows how to hand
one over: Flan's ptr+len, NUL-terminated into a copy for the duration of the
call. [char *] without the const is not that. It is very often a buffer the
callee *writes*, and handing it a temporary copy would lose the writes with
no diagnostic anywhere. const is the only thing in the header that separates
the two, so it is what decides, and a genuine out-buffer keeps a
hand-written binding that says [(Ptr u8)] and means it. *)
let param_ty env (s : string) : Ast.texpr =
let s = String.trim s in
if String.length s > 0 && s.[String.length s - 1] = '*' then begin
let inner = String.trim (String.sub s 0 (String.length s - 1)) in
let is_const = strip_prefix "const " inner <> None in
match bare inner with
| "char" when is_const -> tname "string"
| "char" ->
refuse
"char * is a parameter C may write through, and a Flan string crosses \
as a NUL-terminated copy — the writes would be lost. const char * is \
a string; this one needs a declare-c saying (Ptr u8)"
| _ -> value_ty env s
end
else value_ty env s
(* The return type. Every refusal here is one [Shim] would also make; it is
made earlier so that the reason names the C spelling rather than the Flan
one it was about to become. *)
let ret_ty env (s : string) : Ast.texpr option =
let s = String.trim s in
if bare s = "void" && not (String.contains s '*') then None
else if String.length s > 0 && s.[String.length s - 1] = '*' then begin
let inner = String.trim (String.sub s 0 (String.length s - 1)) in
match bare inner with
| "char" ->
refuse
"returns char *, and a string only crosses as a parameter — a C \
function that returns one returns something Flan has no owner for"
| _ -> Some (value_ty env s)
end
else Some (value_ty env s)
(* ── One header, imported ──────────────────────────────────────────── *)
type imported = {
decls : Ast.decl list;
(* Name and reason, for [Load.refuse_hidden]: the name exists as a thing
that cannot be had, and asking for it says why. Zig's [failDecl]. *)
hidden : (string * string) list;
}
(* [taken] is every name the package already declares, which is what makes the
sidecar additive: a hand-written [(declare-c get-gamepad-name ...)] wins
over the header, and a C symbol already bound by hand is not bound twice —
which [Shim] would refuse for the whole build.
[-c] as well as the name itself, because [Shim] generates [foo-c] beside a
[foo] whose signature has a struct in it, and a collision there is refused
for the whole program rather than for the one binding. *)
let of_dump ~env ~taken ~bound_syms (d : dump) : imported =
let decls = ref [] and hidden = ref [] and by_name = Hashtbl.create 512 in
List.iter
(fun f ->
let flan = kebab f.csym in
let skip why = hidden := (flan, why) :: !hidden in
if List.mem f.csym bound_syms then
(* Not hidden: the name the package wrote for it is there and works.
This is the escape hatch doing its job. *)
()
else if Hashtbl.mem taken flan || Hashtbl.mem taken (flan ^ "-c") then
skip
(Printf.sprintf
"%s would be the imported name of %s, and the package declares \
%s already" flan f.csym flan)
else if Hashtbl.mem by_name flan then
skip
(Printf.sprintf
"%s and %s both kebab to %s, so the header cannot be imported \
whole — one of them needs a hand-written declare-c"
(Hashtbl.find by_name flan) f.csym flan)
else if f.cvariadic then
skip
(Printf.sprintf
"%s is variadic, and a wrapper cannot forward an argument list \
it does not know the shape of" f.csym)
else
match
(try
let ps =
List.mapi
(fun i (n, t) ->
let n = if n = "" then Printf.sprintf "a%d" i else kebab n in
{ Ast.fname = n; fty = param_ty env t; floc = f.cloc })
f.cparams
in
(* [void] spelled as the only parameter is C for "none". clang
reports it as no ParmVarDecl at all, so this is belt and
braces. *)
let ps = List.filter (fun (p : Ast.field) -> p.Ast.fname <> "void") ps in
Ok (ps, ret_ty env f.cret)
with Refused why -> Error why)
with
| Error why -> skip (Printf.sprintf "%s %s" f.csym why)
| Ok (params, ret) ->
Hashtbl.replace by_name flan f.csym;
decls :=
{ Ast.d =
Ast.DeclareC
({ Ast.name = flan; params; ret; fbody = []; nloc = f.cloc },
f.csym);
dloc = f.cloc }
:: !decls)
d.fns;
{ decls = List.rev !decls; hidden = List.rev !hidden }
(* ── Checking the package's layouts against the header's ───────────── *)
(* The point of reading a header that the generator does not otherwise need.
BUILT.md rejected a [_Static_assert] on [sizeof]/[offsetof] as circular:
both sides would have come from the same field list. This is not circular.
The [defstruct] was written by hand and the record comes from the library's
own header, so a disagreement is real information — and it is the failure
mode the whole FFI is most exposed to, since a permuted [Texture2D] reads as
five plausible numbers and no link error.
Reported and not raised. A package may legitimately describe a prefix of a
struct it only ever holds by pointer, and a header that is a different
version of the library is a normal state of affairs to be told about rather
than stopped by. *)
let check_structs ~env ~(structs : (string * Ast.field list) list) (d : dump) =
let record n =
match List.find_opt (fun r -> r.rname = n) d.records with
| Some r -> Some r
| None ->
(* [defstruct Texture2D] against a header whose record is [Texture] and
whose typedef says so. *)
(match List.assoc_opt n d.typedefs with
| Some u -> List.find_opt (fun r -> r.rname = bare u) d.records
| None -> None)
in
(* Names and widths both. Order is what a permuted [defstruct] gets wrong and
what BUILT.md says only a test can catch; width is the other half of the
same hazard and the one it calls out by name — [f64] where the library
says [float] lays out eight bytes where there are four, and every field
after it moves. Comparing the rendered Flan type rather than the C
spelling keeps the two sides commensurable: [u8] and [unsigned char] have
to come out equal, and [f32] and [double] have to not. *)
let field_mismatch (fs : Ast.field list) (r : crecord) =
if List.length fs <> List.length r.rfields then
Some
(Printf.sprintf "defstruct has %d fields [%s] and %s has %d [%s]"
(List.length fs)
(String.concat " " (List.map (fun (f : Ast.field) -> f.Ast.fname) fs))
r.rname (List.length r.rfields)
(String.concat " " (List.map (fun (n, _) -> kebab n) r.rfields)))
else
List.find_map
(fun ((f : Ast.field), (cn, ct)) ->
if kebab cn <> f.Ast.fname then
Some
(Printf.sprintf
"the defstruct has %s where %s has %s — the field order disagrees"
f.Ast.fname r.rname (kebab cn))
else
match (try Some (value_ty env ct) with Refused _ -> None) with
| None -> None (* a field type this cannot render says nothing *)
| Some want ->
let a = ty_source want and b = ty_source f.Ast.fty in
if String.equal a b then None
else
Some
(Printf.sprintf "field %s is %s in the defstruct and %s (%s) in %s"
f.Ast.fname b a ct r.rname))
(List.combine fs r.rfields)
in
List.filter_map
(fun (n, (fs : Ast.field list)) ->
match record n with
| None -> None
| Some r -> Option.map (fun m -> (n, m)) (field_mismatch fs r))
structs
(* ── The entry point ───────────────────────────────────────────────── *)
let dump_of ~loc ~header ~flags =
let text = run_clang ~loc ~header ~flags in
let json =
try Cjson.parse text
with Cjson.Bad m ->
fail loc "clang's AST dump of %s did not parse: %s" header m
in
read_dump ~header json
let env_of ~known_structs ~known_enums d = { known_structs; known_enums; d }
let header ~loc ~header:h ~flags ~known_structs ~known_enums ~taken ~bound_syms =
let d = dump_of ~loc ~header:h ~flags in
let env = env_of ~known_structs ~known_enums d in
(of_dump ~env ~taken ~bound_syms d, d, env)
(* ── Printing a declaration back as source ─────────────────────────── *)
(* Which makes the third option in DISCUSS.md item 6 available at no extra
cost: generate the declarations from the header, *commit the result*, and
regenerate when the library moves. That trade — explicit in the source,
checked against reality, no header read at build time — is a real one, and
it needs a printer and nothing else. [flan import-c] is it. *)
let decl_source (d : Ast.decl) =
match d.Ast.d with
| Ast.DeclareC (fn, csym) ->
Printf.sprintf "(declare-c %s [%s]%s %S)" fn.Ast.name
(String.concat " "
(List.map
(fun (p : Ast.field) ->
Printf.sprintf "%s %s" p.Ast.fname (ty_source p.Ast.fty))
fn.Ast.params))
(match fn.Ast.ret with None -> "" | Some t -> " " ^ ty_source t)
csym
| _ -> ""
(* ── A hand-written binding, against the header's own signature ────── *)
(* The other half of closing the trusted gap, and the one that pays off
immediately: [vendor/raylib] carries 176 [declare-c] lines that were
transcribed by hand from raylib's documentation, and until now nothing could
say whether any of them was right. This says so, one at a time.
Compared as *rendered Flan types*, not as C spellings, because the two sides
are not written in the same language and only the Flan rendering is
commensurable. Three differences are expected and are not reported:
- the Flan name. [IsKeyPressed] is [key-pressed?] by hand and
[is-key-pressed] by rule, and the hand-written one is better. The C symbol
is what identifies the function here, not the name.
- an enum parameter. The header says [KeyboardKey] and the importer has no
way to know the package calls that [Key], so it says [i32]; the
hand-written [Key] is the same int with a better face.
- a [(Ptr T)] where the header says [T *] and the hand-written line chose
something more specific for a reason it recorded.
What is left after those is a real disagreement about a width, an arity or a
direction — which is exactly the class of bug BUILT.md warns about, where
[f64] against the library's [float] reads as garbage rather than as a link
error. *)
type sig_diff = { dsym : string; dflan : string; dwhy : string }
let diff_bound ~env ~(bound : (Ast.fn * string) list) (d : dump) =
let by_sym = Hashtbl.create 512 in
List.iter (fun f -> Hashtbl.replace by_sym f.csym f) d.fns;
List.filter_map
(fun ((fn : Ast.fn), csym) ->
match Hashtbl.find_opt by_sym csym with
| None ->
Some
{ dsym = csym; dflan = fn.Ast.name;
dwhy = "the header does not declare this function at all" }
| Some c ->
let say why = Some { dsym = csym; dflan = fn.Ast.name; dwhy = why } in
(* An enum on the Flan side against a plain int from the header is
the expected difference and not a finding — that is what a Flan
[defenum] *is* at the boundary, and giving it a name is the whole
point of declaring one. Signedness goes with it: raylib spells
[IsGestureDetected]'s parameter [unsigned int] and the package
calls it [Gesture], and since both are four bytes in a register
there is no ABI difference to report. What is still reported is an
enum against something that is *not* a 32-bit integer, which would
be a real one. *)
let enum_like (t : Ast.texpr) =
match t.Ast.t with
| Ast.Tname n -> List.mem n env.known_enums
| _ -> false
in
let int32_like s = String.equal s "i32" || String.equal s "u32" in
let norm (t : Ast.texpr) = ty_source t in
let same a b =
String.equal (norm a) (norm b)
|| (enum_like a && int32_like (norm b))
|| (enum_like b && int32_like (norm a))
in
if c.cvariadic then None
else if List.length fn.Ast.params <> List.length c.cparams then
say
(Printf.sprintf "declared with %d parameters and the header says %d (%s)"
(List.length fn.Ast.params) (List.length c.cparams)
(String.concat ", " (List.map snd c.cparams)))
else
let param_diff =
List.find_map
(fun ((p : Ast.field), (_, ct)) ->
match (try Some (param_ty env ct) with Refused _ -> None) with
| None -> None
| Some want ->
if same want p.Ast.fty then None
else
Some
(Printf.sprintf "parameter %s is %s and the header says %s (%s)"
p.Ast.fname (ty_source p.Ast.fty) (norm want) ct))
(List.combine fn.Ast.params c.cparams)
in
match param_diff with
| Some why -> say why
| None ->
(match (try Ok (ret_ty env c.cret) with Refused w -> Error w) with
| Error _ -> None
| Ok want ->
let agrees =
match (want, fn.Ast.ret) with
| None, None -> true
| Some a, Some b -> same a b
| _ -> false
in
if agrees then None
else
say
(Printf.sprintf "returns %s and the header says %s (%s)"
(match fn.Ast.ret with None -> "nothing" | Some t -> ty_source t)
(match want with None -> "nothing" | Some t -> ty_source t)
c.cret)))
bound

174
lib/cjson.ml Normal file
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@ -0,0 +1,174 @@
(** Just enough JSON to read clang's AST dump.
Not a general JSON library and not a dependency. The compiler's build
inputs are a [clang] on PATH and nothing else — that is plan.org's "Why
LLVM IR as text" applied a second time — so reading clang's
[-ast-dump=json] must not drag in an opam package to parse it. What the
dump actually contains is a narrow subset: objects, arrays, strings,
integers, [true]/[false]/[null]. No floats appear in a declaration dump,
but one is accepted anyway rather than being a lurking parse error.
The reader is strict about structure and lax about what it keeps: a dump of
raylib.h is 1.8 MB and roughly fifty thousand objects, almost all of it
source ranges nobody asks for. Parsing it whole and then selecting is still
well under the cost of the [clang] process that produced it, so there is no
streaming filter here and no reason for one. *)
type t =
| Null
| Bool of bool
| Num of float
| Str of string
| Arr of t list
| Obj of (string * t) list
exception Bad of string
let bad fmt = Printf.ksprintf (fun m -> raise (Bad m)) fmt
let parse (s : string) : t =
let n = String.length s in
let i = ref 0 in
let peek () = if !i < n then s.[!i] else '\000' in
let rec skip_ws () =
if !i < n then
match s.[!i] with
| ' ' | '\t' | '\n' | '\r' -> incr i; skip_ws ()
| _ -> ()
in
let expect c =
if !i >= n || s.[!i] <> c then
bad "expected %c at byte %d" c !i
else incr i
in
let lit word v =
let l = String.length word in
if !i + l <= n && String.sub s !i l = word then (i := !i + l; v)
else bad "bad literal at byte %d" !i
in
(* Strings are the hot path — every node has several — so the common case of
no escape at all is copied out in one [String.sub] rather than a character
at a time through a Buffer. *)
let string_ () =
expect '"';
let start = !i in
let rec scan plain =
if !i >= n then bad "unterminated string at byte %d" start
else
match s.[!i] with
| '"' -> plain
| '\\' -> i := !i + 2; scan false
| _ -> incr i; scan plain
in
let plain = scan true in
if plain then begin
let r = String.sub s start (!i - start) in
incr i; r
end
else begin
let b = Buffer.create (!i - start) in
let j = ref start in
while !j < !i do
(match s.[!j] with
| '\\' ->
incr j;
(match s.[!j] with
| 'n' -> Buffer.add_char b '\n'
| 't' -> Buffer.add_char b '\t'
| 'r' -> Buffer.add_char b '\r'
| 'b' -> Buffer.add_char b '\b'
| 'f' -> Buffer.add_char b '\012'
| '/' -> Buffer.add_char b '/'
| '"' -> Buffer.add_char b '"'
| '\\' -> Buffer.add_char b '\\'
| 'u' ->
(* clang escapes a non-ASCII identifier or a comment this way.
Encoded as UTF-8; a surrogate pair is not joined, which is
acceptable because nothing this reads is ever a name Flan
could use anyway. *)
let hex = String.sub s (!j + 1) 4 in
j := !j + 4;
let c = int_of_string ("0x" ^ hex) in
if c < 0x80 then Buffer.add_char b (Char.chr c)
else if c < 0x800 then begin
Buffer.add_char b (Char.chr (0xC0 lor (c lsr 6)));
Buffer.add_char b (Char.chr (0x80 lor (c land 0x3F)))
end
else begin
Buffer.add_char b (Char.chr (0xE0 lor (c lsr 12)));
Buffer.add_char b (Char.chr (0x80 lor ((c lsr 6) land 0x3F)));
Buffer.add_char b (Char.chr (0x80 lor (c land 0x3F)))
end
| c -> bad "unknown escape \\%c at byte %d" c !j)
| c -> Buffer.add_char b c);
incr j
done;
incr i;
Buffer.contents b
end
in
let number () =
let start = !i in
if peek () = '-' then incr i;
let digits () = while !i < n && s.[!i] >= '0' && s.[!i] <= '9' do incr i done in
digits ();
if peek () = '.' then (incr i; digits ());
if peek () = 'e' || peek () = 'E' then begin
incr i;
if peek () = '+' || peek () = '-' then incr i;
digits ()
end;
if !i = start then bad "expected a number at byte %d" start;
Num (float_of_string (String.sub s start (!i - start)))
in
let rec value () =
skip_ws ();
match peek () with
| '{' ->
incr i; skip_ws ();
if peek () = '}' then (incr i; Obj [])
else begin
let acc = ref [] in
let rec members () =
skip_ws ();
let k = string_ () in
skip_ws (); expect ':';
let v = value () in
acc := (k, v) :: !acc;
skip_ws ();
if peek () = ',' then (incr i; members ()) else expect '}'
in
members ();
Obj (List.rev !acc)
end
| '[' ->
incr i; skip_ws ();
if peek () = ']' then (incr i; Arr [])
else begin
let acc = ref [] in
let rec items () =
let v = value () in
acc := v :: !acc;
skip_ws ();
if peek () = ',' then (incr i; items ()) else expect ']'
in
items ();
Arr (List.rev !acc)
end
| '"' -> Str (string_ ())
| 't' -> lit "true" (Bool true)
| 'f' -> lit "false" (Bool false)
| 'n' -> lit "null" Null
| _ -> number ()
in
let v = value () in
skip_ws ();
if !i <> n then bad "trailing bytes at %d" !i;
v
(* ── Getters ───────────────────────────────────────────────────────── *)
let mem k = function Obj kvs -> List.assoc_opt k kvs | _ -> None
let str k j = match mem k j with Some (Str s) -> Some s | _ -> None
let bool k j = match mem k j with Some (Bool b) -> b | _ -> false
let arr k j = match mem k j with Some (Arr l) -> l | _ -> []