internal/core/eval: re-allow ... with embeddings

Fixes #552

Change-Id: I95583aa5f2d532fa10bc54f6be2466b6771f7298
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7401
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

cue/testdata/definitions/037_closing_with_comprehensions.txtar

@@ -104,7 +104,6 @@ a: _|_ // field "f3" not allowed in closed struct
 }
 -- out/eval --
 Errors:
-#D: cannot mix bulk optional fields with dynamic fields, embeddings, or comprehensions within the same struct
 #E: field `f3` not allowed:
     ./in.cue:1:5
     ./in.cue:27:5
@@ -127,8 +126,7 @@ Result:
   #C: (#struct){
     f1: (int){ int }
   }
-  #D: (_|_){
-    // [eval] #D: cannot mix bulk optional fields with dynamic fields, embeddings, or comprehensions within the same struct
+  #D: (#struct){
     f1: (int){ int }
   }
   #E: (_|_){

cue/testdata/eval/embed.txtar

@@ -0,0 +1,77 @@
+-- in.cue --
+#A: {
+    Common
+    ...
+}
+
+Common: {
+    a: int
+    b: int
+}
+
+x: #A
+x: {
+    c: int
+}
+
+#B: {
+    if true {
+        a: int
+    }
+    ...
+}
+
+y: #B
+y: {
+    c: int
+}
+
+-- out/eval --
+(struct){
+  #A: (#struct){
+    a: (int){ int }
+    b: (int){ int }
+  }
+  Common: (struct){
+    a: (int){ int }
+    b: (int){ int }
+  }
+  x: (#struct){
+    a: (int){ int }
+    b: (int){ int }
+    c: (int){ int }
+  }
+  #B: (#struct){
+    a: (int){ int }
+  }
+  y: (#struct){
+    c: (int){ int }
+    a: (int){ int }
+  }
+}
+-- out/compile --
+--- in.cue
+{
+  #A: {
+    〈1;Common〉
+    ...
+  }
+  Common: {
+    a: int
+    b: int
+  }
+  x: 〈0;#A〉
+  x: {
+    c: int
+  }
+  #B: {
+    if true {
+      a: int
+    }
+    ...
+  }
+  y: 〈0;#B〉
+  y: {
+    c: int
+  }
+}

internal/core/eval/eval.go

@@ -1542,7 +1542,6 @@ func (n *nodeContext) addStruct(
 		case *adt.Ellipsis:
 			n.aStruct = s
 			n.aStructID = closeID
-			hasBulk = x
 			opt.AddEllipsis(ctx, x)
 
 		default: