Use minimal prelude libdefs when no_flowlibs=true

Summary:
Now that infer and merge are a single phase, we can rely on dependencies being
always concrete. This means that we can lookup builtins with abandon -- and we
should, too!

In follow-up diffs, I will work to ensure that NumT, StrT, ArrT, ObjProtoT, etc.
behave correctly with respect to their backing builtin instance types. In
general, this means doing more lookups than we did before. When the no_flowlibs
setting is enabled, all of these lookups would fail.

Since our tests use this option, the situation is particularly hard to ignore.
Instead of always using flowlibs (slow) and writing bespoke flowlibs for every
test (painstaking), this diff ensures that Flow always uses a *minimal* set of
libdefs, which I am calling the prelude.

The prelude includes anything that Flow looks up by name (except some React
specific stuff), including "Object" and "$Iterable", but nothing else. This is
not intended to be usable. There's no Object.prototype.toString, for example.

Reviewed By: avikchaudhuri

Differential Revision: D5263399

fbshipit-source-id: 3f51af0414ffd468622625a984fcf15664305363

Author: samwgoldman

Makefile

@@ -138,6 +138,9 @@ OCP_BUILD_FILES=\
 COPIED_FLOWLIB=\
 	$(foreach lib,$(wildcard lib/*.js),_build/$(lib))
 
+COPIED_PRELUDE=\
+	$(foreach lib,$(wildcard prelude/*.js),_build/$(lib))
+
 JS_STUBS=\
 	$(wildcard js/*.js)
 
@@ -200,7 +203,7 @@ clean-ocp: clean
 	[ -d _obuild ] && ocp-build clean || true
 	rm -f $(OCP_BUILD_FILES)
 
-build-flow: _build/scripts/ppx_gen_flowlibs.native $(BUILT_OBJECT_FILES) $(COPIED_FLOWLIB)
+build-flow: _build/scripts/ppx_gen_flowlibs.native $(BUILT_OBJECT_FILES) $(COPIED_FLOWLIB) $(COPIED_PRELUDE)
 	ocamlbuild \
 		-use-ocamlfind -pkgs sedlex \
 		-no-links  $(INCLUDE_OPTS) $(LIB_OPTS) \
@@ -215,6 +218,7 @@ build-flow-with-ocp: $(OCP_BUILD_FILES) hack/utils/get_build_id.gen.c
 	[ -d _obuild ] || ocp-build init
 	 # Force us to pick up libdef changes - ocp-build is fast so it's fine
 	rm -rf _obuild/flow-flowlib
+	rm -rf _obuild/flow-prelude
 	ocp-build build flow
 	mkdir -p bin
 	cp _obuild/flow/flow.asm$(EXE) bin/flow$(EXE)
@@ -230,7 +234,7 @@ test-parser-ocp: $(OCP_BUILD_FILES) hack/utils/get_build_id.gen.c
 	ocp-build tests flow-parser-hardcoded-test
 	rm -f $(OCP_BUILD_FILES)
 
-build-flow-debug: _build/scripts/ppx_gen_flowlibs.native $(BUILT_OBJECT_FILES) $(COPIED_FLOWLIB)
+build-flow-debug: _build/scripts/ppx_gen_flowlibs.native $(BUILT_OBJECT_FILES) $(COPIED_FLOWLIB) $(COPIED_PRELUDE)
 	ocamlbuild \
 		-use-ocamlfind -pkgs sedlex \
 		-no-links $(INCLUDE_OPTS) $(LIB_OPTS) \
@@ -262,6 +266,11 @@ $(COPIED_FLOWLIB): _build/%.js: %.js
 	cp $< $@
 	rm -rf _build/src/flowlib
 
+$(COPIED_PRELUDE): _build/%.js: %.js
+	mkdir -p $(dir $@)
+	cp $< $@
+	rm -rf _build/src/prelude
+
 _build/scripts/ppx_gen_flowlibs.native: scripts/ppx_gen_flowlibs.ml
 	ocamlbuild \
 		-use-ocamlfind -pkgs sedlex,compiler-libs.common,unix \

_tags

@@ -2,7 +2,7 @@
 <hack/heap/*.ml*>: warn(-27-34)
 <hack/third-party/core/result.ml>: warn(-41)
 <hack/utils/*.ml*>: warn(-3-27)
-<src/flowlib/flowlib.ml>: ppx(scripts/ppx_gen_flowlibs.native lib/)
+<src/flowlib/flowlib.ml>: ppx(scripts/ppx_gen_flowlibs.native lib/ prelude/)
 <src/parser/*.ml*>: warn(-39)
 <**/node_modules/**>: -traverse
 <_obuild>: -traverse

ocp_build_flow.ocp.fb

@@ -191,7 +191,7 @@ begin library "flow-flowlib"
     "flow-ppx-gen-flowlib:asm"
   ]
   comp = [
-    "-ppx" "%{flow-ppx-gen-flowlib_FULL_DST_DIR}%/flow-ppx-gen-flowlib.asm lib/"
+    "-ppx" "%{flow-ppx-gen-flowlib_FULL_DST_DIR}%/flow-ppx-gen-flowlib.asm lib/ prelude/"
   ]
 end
 

prelude/prelude.js

@@ -0,0 +1,58 @@
+declare class Object {}
+
+declare class Function {}
+
+declare class Boolean {}
+
+declare class Number {}
+
+declare class String {
+  @@iterator(): Iterator<string>;
+}
+
+declare class RegExp {}
+
+declare class $ReadOnlyArray<+T> {
+  @@iterator(): Iterator<T>;
+}
+
+declare class Array<T> extends $ReadOnlyArray<T> {}
+
+// Promise
+
+declare class Promise<+R> {}
+declare function $await<T>(p: Promise<T> | T): T;
+
+// Iterable/Iterator/Generator
+
+interface $Iterator<+Yield,+Return,-Next> {
+  @@iterator(): $Iterator<Yield,Return,Next>;
+}
+interface $Iterable<+Yield,+Return,-Next> {
+  @@iterator(): $Iterator<Yield,Return,Next>;
+}
+interface Generator<+Yield,+Return,-Next> {
+  @@iterator(): $Iterator<Yield,Return,Next>;
+}
+
+type Iterator<+T> = $Iterator<T,void,void>;
+type Iterable<+T> = $Iterable<T,void,void>;
+
+declare function $iterate<T>(p: Iterable<T>): T;
+
+// Async Iterable/Iterator/Generator
+
+interface $AsyncIterator<+Yield,+Return,-Next> {
+  @@asyncIterator(): $AsyncIterator<Yield,Return,Next>;
+}
+interface $AsyncIterable<+Yield,+Return,-Next> {
+  @@asyncIterator(): $AsyncIterator<Yield,Return,Next>;
+}
+interface AsyncGenerator<+Yield,+Return,-Next> {
+  @@asyncIterator(): $AsyncIterator<Yield,Return,Next>;
+}
+
+type AsyncIterator<+T> = $AsyncIterator<T,void,void>;
+type AsyncIterable<+T> = $AsyncIterable<T,void,void>;
+
+declare function $asyncIterator<T>(p: AsyncIterable<T>): T;

scripts/ppx_gen_flowlibs.ml

@@ -14,7 +14,7 @@ open Ast_mapper
 open Ast_helper
 
 (* Read in all the flowlib files *)
-let get_flowlibs dir =
+let get_libs dir =
  Sys.readdir dir
  |> Array.fold_left (fun acc file ->
     let contents = Script_utils.string_of_file (Filename.concat dir file) in
@@ -23,22 +23,30 @@ let get_flowlibs dir =
 
 (* Turn the (name, contents) list into a PPX ast (string * string) array
  * expression *)
-let contents =
-  let flowlib_dir = Sys.argv.(1) in
-  get_flowlibs flowlib_dir
+let contents lib_dir =
+  get_libs lib_dir
   |> List.map (fun (name, contents) -> Exp.tuple [
       Exp.constant (Const.string name); Exp.constant (Const.string contents);
     ])
   |> Exp.array
 
 (* Whenever we see [%flowlib_contents], replace it wil the flowlib contents *)
-let ppx_gen_flowlibs_mapper _argv =
- { default_mapper with
-   expr = fun mapper expr ->
-     match expr with
-     | { pexp_desc = Pexp_extension ({ txt = "flowlib_contents"; _ }, PStr []); _} ->
-       contents
-     | other -> default_mapper.expr mapper other; }
+let ppx_gen_flowlibs_mapper argv =
+  let flowlib_contents, prelude_contents =
+    match argv with
+    | [flowlib_dir; prelude_dir] -> contents flowlib_dir, contents prelude_dir
+    | _ ->
+      failwith
+        (Printf.sprintf "Expected two arguments, got %d." (List.length argv))
+  in
+  { default_mapper with
+    expr = fun mapper expr ->
+      match expr with
+      | { pexp_desc = Pexp_extension ({ txt = "flowlib_contents"; _ }, PStr []); _} ->
+        flowlib_contents
+      | { pexp_desc = Pexp_extension ({ txt = "prelude_contents"; _ }, PStr []); _} ->
+        prelude_contents
+      | other -> default_mapper.expr mapper other; }
 
- let () =
-   register "ppx_gen_flowlibs" ppx_gen_flowlibs_mapper
+  let () =
+    register "ppx_gen_flowlibs" ppx_gen_flowlibs_mapper

src/commands/commandUtils.ml

@@ -299,10 +299,10 @@ let collect_flowconfig_flags main ignores_str includes_str lib_str lints_str =
   main { ignores; includes; libs; raw_lint_severities; }
 
 let file_options =
-  let default_lib_dir tmp_dir =
+  let default_lib_dir ~no_flowlib tmp_dir =
     let root = Path.make (Tmp.temp_dir tmp_dir "flowlib") in
     try
-      Flowlib.extract_flowlib root;
+      Flowlib.extract_flowlib ~no_flowlib root;
       root
     with _ ->
       let msg = "Could not locate flowlib files" in
@@ -352,9 +352,9 @@ let file_options =
   in
   fun ~root ~no_flowlib ~temp_dir ~includes ~ignores ~libs flowconfig ->
     let default_lib_dir =
-      if no_flowlib || FlowConfig.no_flowlib flowconfig
-      then None
-      else Some (default_lib_dir temp_dir) in
+      let no_flowlib = no_flowlib || FlowConfig.no_flowlib flowconfig in
+      Some (default_lib_dir ~no_flowlib temp_dir)
+    in
     let ignores = ignores_of_arg
       root
       (FlowConfig.ignores flowconfig)

src/flowlib/flowlib.ml

@@ -8,11 +8,14 @@
  *
  *)
 
-let contents = [%flowlib_contents]
+let contents no_flowlib =
+  if no_flowlib
+  then [%prelude_contents]
+  else [%flowlib_contents]
 
 let write_flowlib dir (filename, contents) =
   let file = Path.(concat dir filename |> to_string) in
   Sys_utils.write_file ~file contents
 
-let extract_flowlib dir =
-  Array.iter (write_flowlib dir) contents
+let extract_flowlib ~no_flowlib dir =
+  Array.iter (write_flowlib dir) (contents no_flowlib)

src/flowlib/flowlib.mli

@@ -8,4 +8,4 @@
  *
  *)
 
-val extract_flowlib : Path.t -> unit
+val extract_flowlib : no_flowlib:bool -> Path.t -> unit