cmd/cue: test tool/exec.Run with arguments involving spaces

The command is expected to fail, as we run the "false" program
which always fails and ignores any arguments.

The printed error is ambiguous, as it's not possible to see
what the original list of arguments was, hence the TODO.
The following commit will resolve this bug.

For #3238.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ie277772ce58dfac48df9440e0a53fd9f1fc309cc
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1197451
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mvdan

cmd/cue/cmd/testdata/script/cmd_errcode.txtar

@@ -16,4 +16,5 @@ command: errcode: {
 		kind:   "exec"
 		cmd:    "ls --badflags"
 		stderr: string // suppress error message
-	}}
+	}
+}

cmd/cue/cmd/testdata/script/cmd_execerr.txtar

@@ -4,6 +4,11 @@ cmp stderr cannotFail-stderr.golden
 exec cue cmd canFail
 cmp stdout canFail-stdout.golden
 
+# TODO(mvdan): the error message should quote the argument list
+# so that any arguments with spaces do not introduce ambiguity.
+! exec cue cmd withSpaces
+cmp stderr withSpaces-stderr.golden
+
 -- cue.mod/module.cue --
 module: "example.com"
 language: version: "v0.9.0"
@@ -18,6 +23,8 @@ hasStderr=false
 errNotFound:
 success=false
 hasStderr=true
+-- withSpaces-stderr.golden --
+task failed: command "false with an ignored argument" failed: exit status 1
 -- foo_tool.cue --
 package foo
 
@@ -55,3 +62,7 @@ command: canFail: {
 			"""
 	}
 }
+
+command: withSpaces: exec.Run & {
+	cmd: ["false", "with an ignored argument"]
+}