Reason V4 [Stacked Diff 3/n #2614] [Parse Hashtags for polymorphic variants]

Summary:

Implements parsing for "hashtags" polymorphic variant constructors.
Since Reason Syntax still supports object syntax, we needed to rearrange
some syntactic real estate to make this work.

```reason
let red = #FF000;

let isRed = color => switch(color) {
  | #FF0000 => true
  | _ => false
};

let callAMethod = someObject::methodName(isRed, "testing red");

let templateLiteral = `
  String template literals are still using backticks.
  String template literals are still using backticks.
`;

```

Test Plan:

Reviewers:

CC:

Author: jordwalke

formatTest/typeCheckedTests/expected_output/arityConversion.re

@@ -1,4 +1,5 @@
 [@reason.version 3.7];
+
 Some((1, 2, 3));
 
 type bcd =

formatTest/typeCheckedTests/expected_output/attributes.re

@@ -7,9 +7,9 @@
  * 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*/;
+[@reason.version 3.7];
 
 /**
  * Core language features:

formatTest/typeCheckedTests/expected_output/autoUpgradeAngleBrackets.re

@@ -0,0 +1,14 @@
+/**
+ * Even if you have an explicit v3.6 marker.
+ * This whole file wil be auto-upaded to 3.8 becase something uses
+ * angle brackets.
+ */;
+[@reason.version 3.8];
+let watchThisIsOldStyle: list<int> = [1, 2];
+
+let watchThisIsOldStylePoly = #hello;
+
+/**
+ * This will cause the whole file to be promoted.
+ */
+let x: list<int> = [1, 3];

formatTest/typeCheckedTests/expected_output/autoUpgradeAngleBracketsNoVersionAttr.re

@@ -0,0 +1,13 @@
+[@reason.version 3.8];
+/**
+ * Test auto-promotion based on feature inference even if no version
+ * tag. By default you're using the old 3.7.
+ */
+let watchThisIsOldStyle: list<int> = [1, 2];
+
+let watchThisIsOldStylePoly = #hello;
+
+/**
+ * This will cause the whole file to be promoted.
+ */
+let x: list<int> = [1, 3];

formatTest/typeCheckedTests/expected_output/autoUpgradeDoNotAutoUpgrade.re

@@ -0,0 +1,5 @@
+[@reason.version 3.7];
+/**
+ * This should just print a 3.7 version attr at the top.
+ */
+let watchThisIsOldStyle: list(int) = [1, 2];

formatTest/typeCheckedTests/expected_output/comments.re

@@ -1,10 +1,9 @@
 /* **** comment */
 /*** comment */
-/** docstring */;
+/*** docstring */
 [@reason.version 3.7];
-
 /* comment */
-/** docstring */;
+/*** docstring */
 /*** comment */
 /**** comment */
 /***** comment */

formatTest/typeCheckedTests/expected_output/comments.rei

@@ -1,15 +1,14 @@
 /* **** comment */
 /*** comment */
 /*** docstring */
+[@reason.version 3.7];
 /* comment */
 /*** docstring */
 /*** comment */
 /**** comment */
 /***** comment */
 
 /** */;
-[@reason.version 3.7];
-
 /*** */
 /**** */
 

formatTest/typeCheckedTests/expected_output/mlSyntax.re

@@ -1,8 +1,8 @@
 /* Copyright (c) 2015-present, Facebook, Inc. All rights reserved. */
 
-/**
+/***
  * Testing pattern matching using ml syntax to exercise nesting of cases.
- */;
+ */
 [@reason.version 3.7];
 
 type xyz =

formatTest/typeCheckedTests/expected_output/oo_3_dot_8.re

@@ -2,13 +2,36 @@
 
 [@reason.version 3.8];
 
+type canStillDefineConst =
+  | []
+  | ::(int, canStillDefineConst);
+
 class virtual stack <'a> (init) = {
+  as self;
   /*
    * The "as this" is implicit and will be formatted away.
    */
   val virtual dummy: unit;
   val mutable v: list<'a> = init;
   pub virtual implementMe: int => int;
+  pub is_empty = () =>
+    switch (v) {
+    | [] => true
+    | _ => false
+    };
+  pub is_empty_unitless =
+    switch (v) {
+    | [] => true
+    | _ => false
+    };
+  pub empty_unitless = {
+    v = [];
+    self;
+  };
+  pub empty = () => {
+    v = [];
+    self;
+  };
   pub pop =
     switch (v) {
     | [hd, ...tl] =>
@@ -90,6 +113,15 @@ class extendedStackAcknowledgeOverride
 
 let inst = (new extendedStack)([1, 2]);
 
+let wasItFull =
+  !inst::empty()::empty_unitless::is_empty();
+// this is the same
+let wasItFull' =
+  !inst::empty()::empty_unitless::is_empty();
+
+let orig_not = (!);
+let (!) = o => o::empty();
+
 /**
  * Recursive classes.
  */
@@ -195,7 +227,7 @@ let acceptsOpenAnonObjAsArg =
         y: int,
       },
     ) =>
-  o#x + o#y;
+  o::x + o::y;
 let acceptsClosedAnonObjAsArg =
     (
       o: {
@@ -204,7 +236,7 @@ let acceptsClosedAnonObjAsArg =
         y: int,
       },
     ) =>
-  o#x + o#y;
+  o::x + o::y;
 let res =
   acceptsOpenAnonObjAsArg({
     pub x = 0;
@@ -346,13 +378,13 @@ let x: tupleClass<int, int> = {
   pub pr = (10, 10)
 };
 
-let x: #tupleClass<int, int> = x;
+let x: *tupleClass<int, int> = x;
 
 let incrementMyClassInstance:
-  (int, #tupleClass<int, int>) =>
-  #tupleClass<int, int> =
+  (int, *tupleClass<int, int>) =>
+  *tupleClass<int, int> =
   (i, inst) => {
-    let (x, y) = inst#pr;
+    let (x, y) = inst::pr;
     {pub pr = (x + i, y + i)};
   };
 
@@ -361,7 +393,7 @@ class myClassWithNoTypeParams = {};
  * The #myClassWithNoTypeParams should be treated as "simple"
  */
 type optionalMyClassSubtype<'a> =
-  option<#myClassWithNoTypeParams> as 'a;
+  option<*myClassWithNoTypeParams> as 'a;
 
 /**
  * Remember, "class type" is really "class_instance_type" (which is the type of
@@ -398,7 +430,7 @@ class addablePoint:
           one: addablePointClassType,
           two: addablePointClassType,
         ) =>
-      one#x + two#x + one#y + two#x;
+      one::x + two::x + one::y + two::x;
     pub x: int = init;
     pub y = init;
   };
@@ -412,7 +444,7 @@ class addablePoint2:
           one: addablePointClassType,
           two: addablePointClassType,
         ) =>
-      one#x + two#x + one#y + two#x;
+      one::x + two::x + one::y + two::x;
     pub x: int = init;
     pub y = init;
   };

formatTest/typeCheckedTests/expected_output/typeParameters.re

@@ -1,29 +1,33 @@
 /**
  * Testing type parameters.
  */;
-[@reason.version 3.7];
+[@reason.version 3.8];
 
-type threeThings('t) = ('t, 't, 't);
-type listOf('t) = list('t);
+module type ListItem = {let x: int;};
 
-type underscoreParam(_) =
+let myListOfModules: list<module ListItem> = [];
+
+type threeThings<'t> = ('t, 't, 't);
+type listOf<'t> = list<'t>;
+
+type underscoreParam<_> =
   | Underscored;
-type underscoreParamCovariance(+_) =
+type underscoreParamCovariance<+_> =
   | Underscored;
-type underscoreParamContravariance(-_) =
+type underscoreParamContravariance<-_> =
   | Underscored;
 
-type tickParamCovariance(+'a) =
+type tickParamCovariance<+'a> =
   | Underscored;
-type tickParamContravariance(-'a) =
+type tickParamContravariance<-'a> =
   | Underscored;
 
-let x: option(list('a)) = None;
-type myFunctionType('a) = (
-  list(('a, 'a)),
-  int => option(list('a)),
+let x: option<list<'a>> = None;
+type myFunctionType<'a> = (
+  list<('a, 'a)>,
+  int => option<list<'a>>,
 );
-let funcAnnoted = (~a: list(int)=[0, 1], ()) => a;
+let funcAnnoted = (~a: list<int>=[0, 1], ()) => a;
 
 /**
  * Syntax that would be likely to conflict with lexing parsing of < > syntax.
@@ -46,12 +50,12 @@ let isSuperGreaterThanEqNegFive3 = zero >>= (-5);
 
 let jsx = (~children, ()) => 0;
 
-type t('a) = 'a;
-let optionArg = (~arg: option(t(int))=?, ()) => arg;
+type t<'a> = 'a;
+let optionArg = (~arg: option<t<int>>=?, ()) => arg;
 let optionArgList =
-    (~arg: option(list(list(int)))=?, ()) => arg;
-let defaultJsxArg = (~arg: t(int)=<jsx />, ()) => arg;
-let defaultFalse = (~arg: t(bool)=!true, ()) => arg;
+    (~arg: option<list<list<int>>>=?, ()) => arg;
+let defaultJsxArg = (~arg: t<int>=<jsx />, ()) => arg;
+let defaultFalse = (~arg: t<bool>=!true, ()) => arg;
 /* Doesn't work on master either let defaultTrue = (~arg:t<bool>= !!true) => arg; */
 
 /**