pkg/list: add a regression test for an invalid operand bug fixed in e…

…valv3

The added test case should fail with an invalid operand error,
and evalv3 does so whereas evalv2 silently does nothing.

Closes #3541.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: Ic1a36f26d615533e8fcc3154b8103afa00e37306
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1206350
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

pkg/list/testdata/issues.txtar

@@ -30,6 +30,84 @@ issue1404: {
 	a:   *1 | 2
 	sum: list.Sum([a])
 }
+issue3541: {
+	_test: {
+		one: {
+			num: 2
+			test: num: 6
+		}
+		two: {
+			num: 3
+			test: num: 7
+		}
+		three: {
+			num: 4
+			test: num: 8
+		}
+		four: {
+			num: 5
+			test: num: 9
+		}
+	}
+
+	list.Sum([for key, val in _test {
+		val.num + val.test
+	}])
+}
+-- out/list-v3 --
+Errors:
+0: invalid operands 2 and {num:6} to '+' (type int and struct):
+    ./in.cue:53:3
+    ./in.cue:35:9
+    ./in.cue:36:10
+
+Result:
+issue563: {
+	#MyDef: {
+		name: string
+	}
+	output: [{
+		name: "a"
+	}, {
+		name: "b"
+	}, {
+		name: "c"
+	}, {
+		name: "1"
+	}, {
+		name: "2"
+	}, {
+		name: "3"
+	}]
+}
+issue1404: {
+	a:   *1 | 2
+	sum: 1
+}
+issue3541: _|_ // 0: invalid operands 2 and {num:6} to '+' (type int and struct)
+-- diff/-out/list-v3<==>+out/list --
+diff old new
+--- old
++++ new
+@@ -1,3 +1,10 @@
++Errors:
++0: invalid operands 2 and {num:6} to '+' (type int and struct):
++    ./in.cue:53:3
++    ./in.cue:35:9
++    ./in.cue:36:10
++
++Result:
+ issue563: {
+ 	#MyDef: {
+ 		name: string
+@@ -20,4 +27,4 @@
+ 	a:   *1 | 2
+ 	sum: 1
+ }
+-issue3541: {}
++issue3541: _|_ // 0: invalid operands 2 and {num:6} to '+' (type int and struct)
+-- diff/explanation --
+issue3541: evalv3 correctly spots an invalid operand error which evalv2 drops on the floor.
 -- out/list --
 issue563: {
 	#MyDef: {
@@ -53,3 +131,4 @@ issue1404: {
 	a:   *1 | 2
 	sum: 1
 }
+issue3541: {}