pkg/list: fix list.Unique dedupping

Fixes #797

Change-Id: Iae45ae627d6283027179509aab9546f67fc387be
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/8904
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

pkg/list/list.go

@@ -231,7 +231,7 @@ func MaxItems(a []cue.Value, n int) bool {
 func UniqueItems(a []cue.Value) bool {
 	b := []string{}
 	for _, v := range a {
-		b = append(b, fmt.Sprint(v))
+		b = append(b, fmt.Sprintf("%+v", v))
 	}
 	sort.Strings(b)
 	for i := 1; i < len(b); i++ {

pkg/list/testdata/list.txtar

@@ -31,6 +31,16 @@ concat: {
     t7: x: 1
     t8: x: [1, [2]]
 }
+unique: {
+	issue797: {
+		mylst: [
+			{ foo: "bar" },
+			{ foo: "baz" }
+		]
+
+		_testmylst: list.UniqueItems & [for x in mylst { x.foo } ]
+	}
+}
 -- out/list --
 Errors:
 error in call to list.Concat: cannot use value 1 (type int) as list
@@ -115,4 +125,13 @@ concat: {
 		v: _|_ // error in call to list.Concat: cannot use value 1 (type int) as list (and 1 more errors)
 	}
 }
+unique: {
+	issue797: {
+		mylst: [{
+			foo: "bar"
+		}, {
+			foo: "baz"
+		}]
+	}
+}