fix cast of null-valued union (#6673)

A cast of a null-valued union results in an error.  Fix that so it
results in a null-valued nullable union.

Author: nwt

runtime/sam/expr/function/cast.go

@@ -45,6 +45,7 @@ func (c *cast) Call(args []super.Value) super.Value {
 }
 
 func (c *cast) Cast(from super.Value, to super.Type) super.Value {
+	from = from.Deunion()
 	switch fromType := from.Type(); {
 	case fromType == to:
 		return from
@@ -70,7 +71,6 @@ func (c *cast) Cast(from super.Value, to super.Type) super.Value {
 	case *super.TypeNamed:
 		return c.toNamed(from, to)
 	default:
-		from = from.Under()
 		caster := expr.LookupPrimitiveCaster(c.sctx, to)
 		if caster == nil {
 			return c.error(from, to)
@@ -84,7 +84,6 @@ func (c *cast) error(from super.Value, to super.Type) super.Value {
 }
 
 func (c *cast) toRecord(from super.Value, to *super.TypeRecord) super.Value {
-	from = from.Under()
 	fromRecType := super.TypeRecordOf(from.Type())
 	if fromRecType == nil {
 		return c.error(from, to)
@@ -142,7 +141,6 @@ func derefWithNone(typ *super.TypeRecord, bytes scode.Bytes, name string) (super
 }
 
 func (c *cast) toArrayOrSet(from super.Value, to super.Type) super.Value {
-	from = from.Under()
 	fromInner := super.InnerType(from.Type())
 	toInner := super.InnerType(to)
 	if fromInner == nil {
@@ -196,7 +194,6 @@ func (c *cast) maybeConvertToUnion(vals []super.Value, types map[super.Type]stru
 }
 
 func (c *cast) toMap(from super.Value, to *super.TypeMap) super.Value {
-	from = from.Under()
 	fromType, ok := from.Type().(*super.TypeMap)
 	if !ok {
 		return c.error(from, to)

runtime/ztests/expr/cast/bool.yaml

@@ -17,6 +17,7 @@ input: |
   "false"
   "blah"
   null
+  null::({}|null)
   "1"
   error("bad")
   {x:1}
@@ -39,6 +40,7 @@ output: |
   false
   error({message:"cannot cast to bool",on:"blah"})
   null::(bool|null)
+  null::(bool|null)
   true
   error("bad")
   error({message:"cannot cast to bool",on:{x:1}})

runtime/ztests/expr/cast/bytes.yaml

@@ -8,6 +8,7 @@ input: |
   "bar"::=named
   ""
   null
+  null::({}|null)
   {x:"foo"}
   error("bad")
 
@@ -17,5 +18,6 @@ output: |
   0x626172
   0x
   null::(bytes|null)
+  null::(bytes|null)
   error({message:"cannot cast to bytes",on:{x:"foo"}})
   error("bad")

runtime/ztests/expr/cast/duration.yaml

@@ -11,6 +11,7 @@ input: |
   1::=named
   1e+19
   null
+  null::({}|null)
   error("bad")
   {x:1}
   [1,2]
@@ -26,6 +27,7 @@ output: |
   1ns
   error({message:"cannot cast to duration",on:1e+19})
   null::(duration|null)
+  null::(duration|null)
   error("bad")
   error({message:"cannot cast to duration",on:{x:1}})
   error({message:"cannot cast to duration",on:[1,2]})

runtime/ztests/expr/cast/enum.yaml

@@ -7,11 +7,13 @@ input: |
   "e3"
   0
   null
+  null::({}|null)
   error("bad")
 
 output: |
   "e2"::enum(e1,e2)
   error({message:"no such symbol in enum(e1,e2)",on:"e3"})
   error({message:"cannot cast to enum",on:0})
   null::(null|enum(e1,e2))
+  null::(null|enum(e1,e2))
   error("bad")

runtime/ztests/expr/cast/float.yaml

@@ -12,6 +12,7 @@ input: |
   false
   true
   null
+  null::({}|null)
 
 output: |
   1.5::float16
@@ -41,6 +42,9 @@ output: |
   null::(float16|null)
   null::(float32|null)
   null::(float64|null)
+  null::(float16|null)
+  null::(float32|null)
+  null::(float64|null)
 
 ---
 

runtime/ztests/expr/cast/int.yaml

@@ -14,6 +14,7 @@ input: |
   false
   true
   null
+  null::({}|null)
 
 output: |
   -1::int8
@@ -56,6 +57,10 @@ output: |
   null::(int16|null)
   null::(int32|null)
   null::(int64|null)
+  null::(int8|null)
+  null::(int16|null)
+  null::(int32|null)
+  null::(int64|null)
 
 ---
 

runtime/ztests/expr/cast/ip.yaml

@@ -7,6 +7,7 @@ input: |
   "127.0.0.1"
   "2001:0000:130F:0000:0000:09C0:876A:130B"
   null
+  null::({}|null)
   1.1.1.1
   1.1.1.2::=named
   34
@@ -18,6 +19,7 @@ output: |
   127.0.0.1
   2001:0:130f::9c0:876a:130b
   null::(ip|null)
+  null::(ip|null)
   1.1.1.1
   1.1.1.2
   error({message:"cannot cast to ip",on:34})

runtime/ztests/expr/cast/map.yaml

@@ -7,12 +7,14 @@ input: |
   |{}|
   |{1:|{"2":3,4:"5"}|,"7":8,"9":|{10:[],[]:11,null:null}|}|
   null
+  null::({}|null)
   1
   error("bad")
 
 output: |
   |{}|
-  |{1:|{"2":3,"4":5}|,7:error({message:"cannot cast to |{string:int64}|",on:8}),9:|{"10":error({message:"cannot cast to int64",on:[]::[null]}),"[]":11,error({message:"cannot cast to string",on:null}):error({message:"cannot cast to int64",on:null})}|}|
+  |{1:|{"2":3,"4":5}|,7:error({message:"cannot cast to |{string:int64}|",on:8}),9:|{"10":error({message:"cannot cast to int64",on:[]::[null]}),"[]":11,null::(string|null):null::(int64|null)}|}|
+  null::(null||{int64:|{string:int64}|}|)
   null::(null||{int64:|{string:int64}|}|)
   error({message:"cannot cast to |{int64:|{string:int64}|}|",on:1})
   error("bad")

runtime/ztests/expr/cast/net.yaml

@@ -6,6 +6,7 @@ input: |
   "192.168.1.0/24"
   "2001:db8::/32"
   null
+  null::({}|null)
   10.0.0.0/8
   10.0.0.0/8::=named
   -35
@@ -16,6 +17,7 @@ output: |
   192.168.1.0/24
   2001:db8::/32
   null::(net|null)
+  null::(net|null)
   10.0.0.0/8
   10.0.0.0/8
   error({message:"cannot cast to net",on:-35})