cmd/cue: add more gengotypes test cases for optional=nillable

To make sure that fields which normally generate as interfaces,
pointers, and references to named types will also work as expected.

While here, start using nil conversions for the gotest.go checks,
just so that we can consistently validate what each type ends up as
while at the same time sanity checking they can all be assigned to nil.

For #3760.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I964367b0b945f68bd58b646c5e39dd191a0b40dd
Dispatch-Trailer: {"type":"trybot","CL":1214379,"patchset":1,"ref":"refs/changes/79/1214379/1","targetBranch":"master"}

Author: mvdan

cmd/cue/cmd/testdata/script/exp_gengotypes.txtar

@@ -188,10 +188,10 @@ fail.both."42_LinkedList".types.LinkedList.next: conflicting values "x" and {ite
     ./root/types.cue:43:14
 fail.both.notList: conflicting values [1,2,3] and {embedded2?:int} (mismatched types list and struct):
     ./cuetest/all.cue:5:24
-    ./root/root.cue:122:2
+    ./root/root.cue:131:2
 fail.both.notString: conflicting values "not_a_struct" and {embedded2?:int} (mismatched types string and struct):
     ./cuetest/all.cue:4:24
-    ./root/root.cue:122:2
+    ./root/root.cue:131:2
 fail.cue."11_Int8".types.Int8: invalid value 99999 (out of bound <=127):
     ./cuetest/all.cue:61:30
 fail.cue."12_Int8".types.Int8: invalid value -99999 (out of bound >=-128):
@@ -282,12 +282,21 @@ func main() {
 	zeroRoot.DiscriminatorField = make(map[string]any)
 
 	// Optional fields which use the optional attribute flag.
+
 	zeroRoot.Fields.OptionalBasic = 5
 	zeroRoot.Fields.OptionalList = make([]int64, 0)
 	zeroRoot.Fields.OptionalMap = make(map[string]int64, 0)
-	zeroRoot.Fields.OptionalBasicAttrNillable = new(int64)
-	zeroRoot.Fields.OptionalListAttrNillable = new([]int64)
-	zeroRoot.Fields.OptionalMapAttrNillable = new(map[string]int64)
+
+	zeroRoot.Fields.OptionalTopAttrNillable = (*any)(nil)
+	zeroRoot.Fields.OptionalNullAttrNillable = (**struct{})(nil)
+	zeroRoot.Fields.OptionalBasicAttrNillable = (*int64)(nil)
+	zeroRoot.Fields.OptionalListAttrNillable = (*[]int64)(nil)
+
+	zeroRoot.Fields.OptionalInlineMapAttrNillable = (*map[string]int64)(nil)
+	zeroRoot.Fields.OptionalNamedMapAttrNillable = (*root.NamedMap)(nil)
+	zeroRoot.Fields.OptionalInlineNestedAttrNillable = (*struct{F *[]string `json:"f,omitempty"`})(nil)
+	zeroRoot.Fields.OptionalNamedNestedAttrNillable = (*root.NamedNested)(nil)
+
 	zeroRoot.Fields.OptionalStruct = root.EmptyStruct{}
 	zeroRoot.Fields.OptionalStructAttrType = root.EmptyStruct{}
 	zeroRoot.Fields.OptionalStructAttrZero = root.EmptyStruct{}
@@ -389,9 +398,18 @@ _#overridenNeverGenerate: string
 		optionalList?:  [...int]
 		optionalMap?:   [string]: int
 
+		optionalTopAttrNillable?:   _ @go(,optional=nillable)
+		optionalNullAttrNillable?:  null @go(,optional=nillable)
 		optionalBasicAttrNillable?: int @go(,optional=nillable)
 		optionalListAttrNillable?:  [...int] @go(,optional=nillable)
-		optionalMapAttrNillable?:   {[string]: int} @go(,optional=nillable)
+
+		// Ensure that "is nillable" is worked out correctly for inline types, referenced definitions,
+		// and nested types where only part of the type is not nillable, but not the top level.
+
+		optionalInlineMapAttrNillable?:    {[string]: int} @go(,optional=nillable)
+		optionalNamedMapAttrNillable?:     #namedMap @go(,optional=nillable)
+		optionalInlineNestedAttrNillable?: {f?: [...string]} @go(,optional=nillable)
+		optionalNamedNestedAttrNillable?:  #namedNested @go(,optional=nillable)
 
 		optionalStruct?: #emptyStruct
 		optionalStructAttrType?: #emptyStruct @go(,type=EmptyStruct)
@@ -493,6 +511,10 @@ _#hiddenStruct: {
 	}
 }
 
+#namedMap: [string]: int
+
+#namedNested: f?: [...string]
+
 // Hidden definitions are only generated if referenced; this one is not.
 _#unusedHiddenStruct: neverGenerate?: int
 
@@ -698,11 +720,23 @@ type Root struct {
 
 		OptionalMap map[string]int64 `json:"optionalMap,omitempty"`
 
+		OptionalTopAttrNillable *any/* CUE top */ `json:"optionalTopAttrNillable,omitempty"`
+
+		OptionalNullAttrNillable **struct{}/* CUE null */ `json:"optionalNullAttrNillable,omitempty"`
+
 		OptionalBasicAttrNillable *int64 `json:"optionalBasicAttrNillable,omitempty"`
 
 		OptionalListAttrNillable *[]int64 `json:"optionalListAttrNillable,omitempty"`
 
-		OptionalMapAttrNillable *map[string]int64 `json:"optionalMapAttrNillable,omitempty"`
+		OptionalInlineMapAttrNillable *map[string]int64 `json:"optionalInlineMapAttrNillable,omitempty"`
+
+		OptionalNamedMapAttrNillable *NamedMap `json:"optionalNamedMapAttrNillable,omitempty"`
+
+		OptionalInlineNestedAttrNillable *struct {
+			F *[]string `json:"f,omitempty"`
+		} `json:"optionalInlineNestedAttrNillable,omitempty"`
+
+		OptionalNamedNestedAttrNillable *NamedNested `json:"optionalNamedNestedAttrNillable,omitempty"`
 
 		OptionalStruct EmptyStruct `json:"optionalStruct,omitempty"`
 
@@ -799,6 +833,12 @@ type Root struct {
 
 }
 
+type NamedMap map[string]int64
+
+type NamedNested struct {
+	F []string `json:"f,omitempty"`
+}
+
 type Root_innerStruct struct {
 	InnerStructField int64 `json:"innerStructField,omitempty"`
 }