cue/parser: add test case for string interpolation edge case

The logic for parsing string interpolations assumes that
if there's an open-paren after a segment of a string
interpolation, it's the start of an interpolation expression.

That's not necessarily the case. This CL adds a test case
for this before fixing it in a subsequent CL.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: If272c30278dbe74ae27a95512706d1c1c26e8c7e
Reviewed-on: https://cue.gerrithub.io/c/cue-lang/cue/+/1223784
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: rogpeppe

cue/parser/parser_test.go

@@ -569,6 +569,13 @@ cannot import package as definition identifier`,
 			 '''`,
 			out: `a: "foo \(ident)", b: "bar \(bar)  $$$ ", c: "nest \({a: "\(nest) "}.a) \(5)", m1: """` + "\n\t\t\t multi \\(bar)\n\t\t\t \"\"\", m2: '''\n\t\t\t \\(bar) multi\n\t\t\t '''",
 		},
+		{
+			desc: "paren after interpolation",
+			in:   `"\(1)"()`,
+			// Note: this actually masks an out-of-bounds slice index panic
+			// in scanner.Scanner.popInterpolation.
+			out: "\nexpected operand, found ')' (and 1 more errors)",
+		},
 		{
 			desc: "file comments",
 			in: `// foo