[police] open IStd automatically

Summary:
This should help prevent new modules being created that do not `open! IStd`.

Documented this in CONTRIBUTING.md.

Reviewed By: jberdine

Differential Revision: D5183552

fbshipit-source-id: 0f0a8ce

CONTRIBUTING.md

@@ -71,32 +71,47 @@ us a line at cla@fb.com. Thanks!
 
 ### OCaml
 
-- Follow the ocp-indent style in infer/.ocpindent for indentation.
+- The module IStd (infer/src/base/IStd.ml) is automatically opened in every file. Beware that this
+  can cause weird errors such as:
+```
+$ pwd
+/somewhere/infer/infer/src
+$ cat base/toto.ml
+let b = List.mem true [true; false]
+$ make
+[...]
+File "base/toto.ml", line 1, characters 17-21:
+Error: This variant expression is expected to have type 'a list
+       The constructor true does not belong to type list
+```
 
-- Spaces around binary operators, e.g., `let x = a + 5`.
+  If your new module cannot compile with `IStd`, for instance because it's generated code, modify
+  the line in infer/src/Makefile that adds `-open IStd` so that your module is excluded (see how
+  it's done for other such modules, eg IStd.ml).
 
-- Spaces around parentheses, no space inside parentheses.
+- All modules open `IStd` using `open! IStd`. This is to make that fact more explicit (there's also
+  the compilation flag mentioned above), and also it helps merlin find the right types. In
+  particular this also opens `Core.Std`.
 
-- Spaces around braces and brackets, spaces inside braces and brackets.
+- Do not add anything to `IStd` unless you have a compelling reason to do so, for instance if you
+  find some utility function is missing and is not provided by
+  [`Core`](https://ocaml.janestreet.com/ocaml-core/latest/doc/core/).
 
-- Space after `,` and `;`, e.g. `let (a, b) = ({ foo = 4; }, ())`.
+- Polymorphic equality is disabled; use type-specific equality instead, even for primitive types
+  (e.g., `Int.equal`). However, if your module uses a lot of polymorphic variants with no arguments
+  you may safely `open! PVariant`.
 
-- Terminate multi-line values such as lists and records with `;` so that it's easy to add new lines
-  without modifying existing ones. For instance:
-```OCaml
-let foo = [
-  value1;
-  value2;
-]
+  If you try and use polymorphic equality `=` in your code you will get a compilation error, such as:
+```
+Error: This expression has type int but an expression was expected of type
+         [ `no_polymorphic_compare ]
 ```
 
-- All modules open `IStd`, using `open! IStd`. In particular this also opens `Core.Std`. Do not add
-  anything to `IStd`; if you find some utility function is missing (and not provided by
-  [`Core`](https://ocaml.janestreet.com/ocaml-core/latest/doc/core/)), add it to `Utils`.
+- Alias and use `module L = Logging` for all your logging needs. Refer to its API in Logging.mli for
+  documentation.
 
-- Polymorphic equality is disabled; use type-specific equality instead, even for primitive types
-  (e.g., `Int.equal`). However, if your module uses a lot of polymorphic variants you may
-  `open! PVariant`.
+- Check that your code compiles without warnings with `make -j test_build` (this also runs as part
+  of `make test`).
 
 - Apart from `IStd` and `PVariant`, refrain from globally `open`ing modules. Using local open
   instead when it improves readability: `let open MyModule in ...`.
@@ -129,7 +144,24 @@ module MF = MarkupFormatter
 
 - Use the `_hum` suffix to flag functions that output human-readable strings.
 
-- Check that your code compiles without warnings with `make -j test_build`.
+- Follow the ocp-indent style in infer/.ocpindent for indentation.
+
+- Spaces around binary operators, e.g., `let x = a + 5`.
+
+- Spaces around parentheses, no space inside parentheses.
+
+- Spaces around braces and brackets, spaces inside braces and brackets.
+
+- Space after `,` and `;`, e.g. `let (a, b) = ({ foo = 4; }, ())`.
+
+- Terminate multi-line values such as lists and records with `;` so that it's easy to add new lines
+  without modifying existing ones. For instance:
+```OCaml
+let foo = [
+  value1;
+  value2;
+]
+```
 
 ### Reason
 

infer/src/Makefile

@@ -39,6 +39,7 @@ OCAMLBUILD_OPTIONS = \
   -cflags -w,$(OCAML_FATAL_WARNINGS)-4-9-32-40-41-42-45-48 \
   -tag-line "<*{clang/clang_ast_*,backend/jsonbug_*,checkers/stacktree_*}>: warn(-27-32-34-35-39)" \
   -tag-line "<*/{,*/}*.{ml,re}{,i}>: package(ppx_compare)" \
+  -tag-line "not <**/{IList,IStd,jsonbug_j,clang_ast_j,clang_ast_b,stacktree_j}.*>: open(IStd)" \
   -tag thread \
   -pkgs ANSITerminal,atdgen,cmdliner,core,extlib,oUnit,parmap,str,unix,xmlm,yojson,zip