cue: include package name in debug output for builtins

Change-Id: I11b6ee4179950dc7660e3fb36a26a2c243ed75d8
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2620
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/cue/debug.go b/cue/debug.go
index 25199f4..d7bfede 100644
--- a/cue/debug.go
+++ b/cue/debug.go
@@ -171,8 +171,7 @@
 	case string:
 		write(x)
 	case *builtin:
-		write("builtin:")
-		p.str(x.Name)
+		write(x.name(p.ctx))
 	case *nodeRef:
 		if p.showNodeRef {
 			writef("<%s>", p.ctx.ref(x.node))
diff --git a/cue/resolve_test.go b/cue/resolve_test.go
index 0db51ed..b1227c2 100644
--- a/cue/resolve_test.go
+++ b/cue/resolve_test.go
@@ -741,7 +741,7 @@
 		`,
 		out: `<0>{` +
 			`a: "after", ` +
-			`b: _|_(builtin:ContainsAny ("c"):invalid value "dog" (does not satisfy strings.ContainsAny("c")))` +
+			`b: _|_(strings.ContainsAny ("c"):invalid value "dog" (does not satisfy strings.ContainsAny("c")))` +
 			`}`,
 	}, {
 		desc: "null coalescing",
@@ -1344,7 +1344,7 @@
 			`a3: <3>{a: _|_((=~"oo" & "bar"):invalid value "bar" (does not match =~"oo")), b: =~"oo", c: =~"fo"}, ` +
 			`o1: <4>{a: string, b: string, c: "bar"}, ` +
 			`o2: <5>{a: "foo", b: string, c: "bar"}, ` +
-			`o3: <6>{a: _|_((builtin:or ([<7>.b,<7>.c]) & "foo"):empty disjunction: conflicting values "baz" and "foo"), b: "baz", c: "bar"}}`,
+			`o3: <6>{a: _|_((or ([<7>.b,<7>.c]) & "foo"):empty disjunction: conflicting values "baz" and "foo"), b: "baz", c: "bar"}}`,
 	}, {
 		desc: "self-reference cycles conflicts with strings",
 		in: `
diff --git a/cue/types_test.go b/cue/types_test.go
index d4d6dd1..50a7e76 100644
--- a/cue/types_test.go
+++ b/cue/types_test.go
@@ -2004,7 +2004,7 @@
 		want:  "[:] <0>.a 2 5",
 	}, {
 		input: "v: len([])",
-		want:  "() builtin:len []",
+		want:  "() len []",
 	}, {
 		input: `v: "Hello, \(x)! Welcome to \(place)", place: string, x: string`,
 		want:  `\() "Hello, " <0>.x "! Welcome to " <0>.place ""`,