Make exponentiation operator right-associative (#5959)

* Make exponentiation operator right-associative

* update printer

* chore: format

* update CHANGELOG.md

Author: aspeddro

CHANGELOG.md

@@ -37,6 +37,7 @@ subset of the arguments, and return a curried type with the remaining ones https
 - Curried after uncurried is not fused anymore: `(. x) => y => 3` is not equivalent to `(. x, y) => 3` anymore. It's instead equivalent to `(. x) => { y => 3 }`.
 Also, `(. int) => string => bool` is not equivalen to `(. int, string) => bool` anymore.
 These are only breaking changes for unformatted code.
+- Exponentiation operator `**` is now right-associative. `2. ** 3. ** 2.` now compile to `Math.pow(2, Math.pow(3, 2))` and not anymore `Math.pow(Math.pow(2, 3), 2)`. Parentheses can be used to change precedence.
 
 #### :bug: Bug Fix
 

jscomp/test/build.ninja

@@ -0,0 +1,16 @@
+'use strict';
+
+
+var a = Math.pow(2, Math.pow(3, 2));
+
+var b = Math.pow(2, Math.pow(-3, 2));
+
+var c = Math.pow(Math.pow(2, 3), 2);
+
+var d = Math.pow(-2, 2);
+
+exports.a = a;
+exports.b = b;
+exports.c = c;
+exports.d = d;
+/* a Not a pure module */

jscomp/test/exponentiation_precedence_test.js

@@ -0,0 +1,4 @@
+let a = 2. ** 3. ** 2.
+let b = 2. ** -3. ** 2.
+let c = (2. ** 3.) ** 2.
+let d = (-2.) ** 2.

jscomp/test/exponentiation_precedence_test.res

@@ -2200,7 +2200,11 @@ and parseBinaryExpr ?(context = OrdinaryExpr) ?a p prec =
       let startPos = p.startPos in
       Parser.next p;
       let endPos = p.prevEndPos in
-      let b = parseBinaryExpr ~context p (tokenPrec + 1) in
+      let tokenPrec =
+        (* exponentiation operator is right-associative *)
+        if token = Exponentiation then tokenPrec else tokenPrec + 1
+      in
+      let b = parseBinaryExpr ~context p tokenPrec in
       let loc = mkLoc a.Parsetree.pexp_loc.loc_start b.pexp_loc.loc_end in
       let expr =
         Ast_helper.Exp.apply ~loc

res_syntax/src/res_core.ml

@@ -320,6 +320,11 @@ let isEqualityOperator operator =
   | "=" | "==" | "<>" | "!=" -> true
   | _ -> false
 
+let isRhsBinaryOperator operator =
+  match operator with
+  | "**" -> true
+  | _ -> false
+
 let flattenableOperators parentOperator childOperator =
   let precParent = operatorPrecedence parentOperator in
   let precChild = operatorPrecedence childOperator in

res_syntax/src/res_parsetree_viewer.ml

@@ -77,6 +77,7 @@ val operatorPrecedence : string -> int
 val isUnaryExpression : Parsetree.expression -> bool
 val isBinaryOperator : string -> bool
 val isBinaryExpression : Parsetree.expression -> bool
+val isRhsBinaryOperator : string -> bool
 
 val flattenableOperators : string -> string -> bool
 

res_syntax/src/res_parsetree_viewer.mli

@@ -3672,7 +3672,11 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
         [(Nolabel, lhs); (Nolabel, rhs)] ) ->
     let right =
       let operatorWithRhs =
-        let rhsDoc = printOperand ~isLhs:false rhs operator in
+        let rhsDoc =
+          printOperand
+            ~isLhs:(ParsetreeViewer.isRhsBinaryOperator operator)
+            rhs operator
+        in
         Doc.concat
           [
             printBinaryOperator
@@ -3686,7 +3690,14 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
       else operatorWithRhs
     in
     let doc =
-      Doc.group (Doc.concat [printOperand ~isLhs:true lhs operator; right])
+      Doc.group
+        (Doc.concat
+           [
+             printOperand
+               ~isLhs:(not @@ ParsetreeViewer.isRhsBinaryOperator operator)
+               lhs operator;
+             right;
+           ])
     in
     Doc.group
       (Doc.concat

res_syntax/src/res_printer.ml

@@ -66,6 +66,11 @@ let x = longIdentifier + longIdentifier * longIdentifier * longIdentifier / long
 let x = longIdentifier && longIdentifier && longIdentifier && longIdentifier && longIdentifier && longIdentifier;
 let x = longIdentifier && longIdentifier || longIdentifier && longIdentifier || longIdentifier && longIdentifier;
 
+// exponentiation is right associative
+let x = 2. ** 3. ** 2.
+let x = (2. ** 3.) ** 2.
+let x = 2. ** (3. ** 2.)
+
 if (
   successorParent.color === Black &&
     (sibling === None ||

res_syntax/tests/printer/expr/binary.res

@@ -108,6 +108,11 @@ let x =
   longIdentifier && longIdentifier ||
   (longIdentifier && longIdentifier)
 
+// exponentiation is right associative
+let x = 2. ** 3. ** 2.
+let x = (2. ** 3.) ** 2.
+let x = 2. ** 3. ** 2.
+
 if (
   successorParent.color === Black &&
     (sibling === None ||