Reason V4 [Stacked Diff 1/n #2605] [Allow multiple versions of Reason]

Summary:This allows multiple versions of Reason in a single project by
inferring and recording the version of syntax used into the file in an
attribute. The attribute allows us to switch the parser and lexer on the
fly. This attribute is not the only way we can infer the version, and we
can allow project level configuration, but this is the approach that is
guaranteed to work with any build system or tooling.

Test Plan:

Reviewers:

CC:

Author: jordwalke

docs/RELEASING.md

@@ -16,14 +16,32 @@ and `rtop.json` respectively in the repo root, you would run that script after
 committing/bumping some versions:
 
 
+**IMPORTANT: Update The Version Numbers In Packages:**
+1. Make sure the version number in `esy.json` and `reason.json` is the new
+   version number for the release.
+2. Make sure the file
+   [../../src/reason-version/reason_version.ml](../../src/reason-version/reason_version.ml)
+   also has that same version number that `refmt` has:
+
 ```sh
 git checkout -b MYRELEASE origin/master
 git rebase origin/master
-vim -O esy.json reason.json
-# Then edit the version number accordingly on BOTH files. With that same VERSION do:
-version=3.5.0 make pre_release
+vim -O esy.json reason.json src/reason-version/reason_version.ml
+
+# Edit version field in jsons, and make sure reason_version has the new version
+# let package_version = {
+#   major = 3;
+#   minor = 7;
+#   patch = 0;
+# }
+
 git commit -m "Bump version"
 git push origin HEAD:PullRequestForVersion # Commit these version bumps
+
+```
+
+**Perform The Release:**
+```sh
 node ./scripts/esy-prepublish.js ./reason.json ./rtop.json
 
 # Then publish. For example:

formatTest/typeCheckedTests/expected_output/arityConversion.re

@@ -1,3 +1,4 @@
+[@reason.version 3.7];
 Some((1, 2, 3));
 
 type bcd =

formatTest/typeCheckedTests/expected_output/attributes.4.04.0.re

@@ -1,3 +1,4 @@
+[@reason.version 3.7];
 /* Pexp_letexception with attributes */
 let () = {
   [@attribute]

formatTest/typeCheckedTests/expected_output/attributes.re

@@ -7,6 +7,7 @@
  * This has a nice side effect when printing the terms:
  * If a node has attributes attached to it,
  */;
+[@reason.version 3.7];
 
 /**Floating comment text should be removed*/;
 

formatTest/typeCheckedTests/expected_output/attributes.rei

@@ -1,6 +1,8 @@
 /* Copyright (c) 2015-present, Facebook, Inc. All rights reserved. */
 
 /**Floating comment text should be removed*/;
+[@reason.version 3.7];
+
 let test: int;
 
 /**

formatTest/typeCheckedTests/expected_output/basics.re

@@ -1,3 +1,4 @@
+[@reason.version 3.7];
 /* Copyright (c) 2015-present, Facebook, Inc. All rights reserved. */
 
 let l =

formatTest/typeCheckedTests/expected_output/basics_no_semi.re

@@ -1,3 +1,4 @@
+[@reason.version 3.7];
 /* Copyright (c) 2015-present, Facebook, Inc. All rights reserved. */
 
 let l =

formatTest/typeCheckedTests/expected_output/bigarraySyntax.re

@@ -1,3 +1,4 @@
+[@reason.version 3.7];
 /* https://github.com/facebook/reason/issues/2038 */
 let my_big_array1 =
   Bigarray.Array1.create(

formatTest/typeCheckedTests/expected_output/comments.re

@@ -1,6 +1,8 @@
 /* **** comment */
 /*** comment */
 /** docstring */;
+[@reason.version 3.7];
+
 /* comment */
 /** docstring */;
 /*** comment */

formatTest/typeCheckedTests/expected_output/comments.rei

@@ -8,6 +8,8 @@
 /***** comment */
 
 /** */;
+[@reason.version 3.7];
+
 /*** */
 /**** */