Ticket #117: non-nilable-coalesce.patch

Source/BinaryOpExpr.cobra

@@ -950 +950 @@
         if _left.type is ptt or _right.type is ptt
             # x ? y   ...where either is typed as passthrough
             _type = ptt
+        else if not _left.type inherits NilableType 
+            .throwError('The left hand type of "?" is not nilable (it\'s "[_left.type.name]") so the expression will always evaluate to the left hand side.')
         else if _left.type inherits NilableType and not _right.type inherits NilableType
             # x ? y   ...where x can be nil, but y cannot
             _type = _left.type.nonNil  # TODO: should be greatest common denominator between the two
@@ -999 +1001 @@
 
     def _bindImp
         base._bindImp
-        # TODO: error check that the left hand type is nilable?
+        if not _left.type inherits NilableType  
+            .throwError('The left hand type of "?=" is not nilable (it\'s "[_left.type.name]") so the expression will always evaluate to the left hand side.')
         # TODO: error check that the right hand type is not nilable?
         _type = _right.type
 

Tests/820-errors/200-expressions/134-non-nilable-coalesce.cobra

@@ +1 @@
+# errors on nil coalesce if lhs non-nilable
+class Nilable
+    def main is shared
+        a = 0
+        
+        b = a ? 99 # .error. The left hand type of "?" is not nilable
+        assert  b == 0
+        a = 10
+        b = a ? 99 # .error. The left hand type of "?" is not nilable
+        assert  b == 10
+    
+        a ?= 47 # .error. The left hand type of "?=" is not nilable
+        assert b == 10
+        
+        s = 'yy'
+        assert s ? 'xxx' == 'yy' # .error. The left hand type of "?" is not nilable
+        
+        s ?= 'xxx' # .error. The left hand type of "?=" is not nilable
+        assert s == 'yy'
+        
+        

Tests/240-generics/200-nilables/801-qu-op.cobra

@@ -14 +14 @@
         return _name ? .getType.name  # used to be a bug
 
     def foo
-        s = (Test('foo') ? Test()).name
+        t as Test? = Test('foo')
+        s = (t ? Test()).name    
         assert s=='foo'
+        
         assert (Test().nilableProperty ? 'aoeu') == 'aoeu'
+        
+        # augmented  assign ?=
+        t1 as Test? = Test('foo')
+        t1 ?= Test()
+        s = t1.name
+        assert s=='foo'
 
     get nilableProperty as String?
         return nil

Developer/IntermediateReleaseNotes.text

@@ -392 +392 @@
 * Fixed: Cobra gives an inscrutable error message for numeric for-loops that have incompatible numeric types. ticket:165
 
 * Fixed: Improper codegen for static constructors. ticket:169
+
+* Fixed: Operators ? and ?= give error if lhs expression is not nilable  ticket:117