Compiler: fix code generation for condition (ocsigen#1046)

* Compiler: fix code generation for condition

CHANGES.md

@@ -10,7 +10,8 @@
 * Compiler: fix code generation for recursive function under for-loops (#1009)
 * Compiler: the jsoo compiler compiled to javascript was not behaving correctly
             when parsing constant in the from the bytecode
-* Compiled: make sure inline doesn't loop indefinitly (#1043)
+* Compiler: make sure inline doesn't loop indefinitly (#1043)
+* Compiler: fix bug generating invalid javascript for if-then construct (#1046)
 * Lib: Rename msg to message in Worker (#1037)
 * Lib: fix graphics_js when build with separate compilation (#1029)
 

compiler/lib/js_output.ml

@@ -787,7 +787,6 @@ struct
     | Debugger_statement ->
         PP.string f "debugger";
         last_semi ()
-    | Expression_statement (EVar _) -> last_semi ()
     | Expression_statement e ->
         (* Parentheses are required when the expression
            starts syntactically with "{" or "function" *)

compiler/lib/js_simpl.ml

@@ -120,7 +120,10 @@ let rec if_statement_2 e loc iftrue truestop iffalse falsestop =
   let e = simplify_condition e in
   match fst iftrue, fst iffalse with
   (* Empty blocks *)
-  | J.Block [], J.Block [] -> [ J.Expression_statement e, loc ]
+  | J.Block [], J.Block [] -> (
+      match e with
+      | J.EVar _ -> []
+      | _ -> [ J.Expression_statement e, loc ])
   | J.Block [], _ -> if_statement_2 (enot e) loc iffalse falsestop iftrue truestop
   | _, J.Block [] -> [ J.If_statement (e, iftrue, None), loc ]
   | _ -> (

compiler/tests-compiler/cond.ml

@@ -0,0 +1,66 @@
+(* Js_of_ocaml compiler
+ * http://www.ocsigen.org/js_of_ocaml/
+ * Copyright (C) 2017 Hugo Heuzard
+ * Copyright (C) 2019 Ty Overby
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, with linking exception;
+ * either version 2.1 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *)
+
+open Util
+
+let%expect_test "conditional" =
+  let program =
+    compile_and_parse
+      {|
+    let f a b c d e f =
+    let x = match a,b,c,d,e,f with
+    | true, false, false, false ,false, false -> 1
+    | false, false, false, true, false, false -> 4
+    | false, true, false, false, false ,false -> 2
+    | false, false, true, false, false, false -> 3
+    | false, false, false, false, true, false -> 5
+    | false, false, false, false, false, true -> 6
+    | false, false, false, false, false, false -> 100
+    | true, true, _, _, _, _
+    | _, true, _, true, _, _
+    | _ -> -1
+    in x + 2
+  |}
+  in
+  print_fun_decl program (Some "f");
+  [%expect
+    {|
+    function f(a,b,c,d,e,f)
+     {var switch$0=0;
+      if(a)
+       {if(! b && ! c && ! d && ! e && ! f){var x=1;switch$0 = 1}}
+      else
+       if(b)
+        {var switch$1=0;
+         if(! c && ! d)
+          if(e || f)switch$1 = 1;else{var x=2;switch$0 = 1;switch$1 = 1}}
+       else
+        if(c)
+         {if(! d && ! e && ! f){var x=3;switch$0 = 1}}
+        else
+         if(d)
+          {if(! e && ! f){var x=4;switch$0 = 1}}
+         else
+          if(e)
+           {if(! f){var x=5;switch$0 = 1}}
+          else
+           if(f){var x=6;switch$0 = 1}else{var x=100;switch$0 = 1}
+      if(! switch$0)var x=- 1;
+      return x + 2 | 0} |}]