Revert "tools/flow: check and return errors from task values"

This reverts commit 9ef35eb
but keeps the `cmd_undefined` test case and adds
a new test case (very similar to the test case for #2517)
that illustrates the way that the reverted commit fails.

That commit introduced a regression that caused existing
tools/flow uses to fail. See https://cuelang.org/issue/2965.

A subsequent CL will apply a different fix for #1581.

For #2965.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I322ac3b269bc79a541c15001a166160ad9191267
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1185281
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@gmail.com>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
(cherry picked from commit ea385fd)
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1190978
Reviewed-by: Paul Jolly <paul@myitcv.io>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

cmd/cue/cmd/testdata/script/cmd_undefined.txtar

@@ -1,9 +1,18 @@
-! exec cue cmd tool
-stderr 'command.tool.bad: undefined field: DoesntExist'
-! exec cue cmd builtin
-stderr 'command.builtin.bad: undefined field: DoesntExist'
-! exec cue cmd package
-stderr 'command.package.bad: undefined field: DoesntExist'
+# This test illustrates the problem demonstrated
+# in https://github.com/cue-lang/cue/issues/1581
+# TODO fix tools/flow so it fails in this case.
+
+# TODO this should not succeed
+exec cue cmd tool
+# stderr 'command.tool.bad: undefined field: DoesntExist'
+
+# TODO this should not succeed
+exec cue cmd builtin
+# stderr 'command.builtin.bad: undefined field: DoesntExist'
+
+# TODO this should not succeed
+exec cue cmd package
+# stderr 'command.package.bad: undefined field: DoesntExist'
 -- cue.mod/module.cue --
 module: "mod.test/test"
 -- sub/sub.cue --

tools/flow/tasks.go

@@ -91,10 +91,6 @@ func (c *Controller) findRootTasks(v cue.Value) {
 
 // getTask finds and marks tasks that are descendents of v.
 func (c *Controller) getTask(scope *Task, v cue.Value) *Task {
-	if err := v.Err(); err != nil {
-		c.addErr(err, "invalid task")
-		return nil
-	}
 	// Look up cached node.
 	_, w := value.ToInternal(v)
 	if t, ok := c.nodes[w]; ok {

tools/flow/testdata/issue2965.txtar

@@ -0,0 +1,83 @@
+#IgnoreConcrete: true
+#InferTasks: true
+-- in.cue --
+package x
+
+root: {
+	prepare: {
+		$id: "prepare"
+		stdout: string
+	}
+	env2: {
+		// Note: the string interpolation here is the only difference
+		// from issue2517.txtar. It makes the value incomplete
+		// rather than just non-concrete.
+		input: "\(prepare.stdout)"
+	}
+	run: {
+		$id: "run"
+		env: env2
+	}
+}
+-- out/run/errors --
+-- out/run/t0 --
+graph TD
+  t0("root.prepare [Ready]")
+  t1("root.run [Waiting]")
+  t1-->t0
+
+-- out/run/t1 --
+graph TD
+  t0("root.prepare [Terminated]")
+  t1("root.run [Ready]")
+  t1-->t0
+
+-- out/run/t1/value --
+{
+	$id:    "prepare"
+	stdout: "foo"
+}
+-- out/run/t1/stats --
+Leaks:  0
+Freed:  11
+Reused: 6
+Allocs: 5
+Retain: 0
+
+Unifications: 11
+Conjuncts:    16
+Disjuncts:    11
+-- out/run/t2 --
+graph TD
+  t0("root.prepare [Terminated]")
+  t1("root.run [Terminated]")
+  t1-->t0
+
+-- out/run/t2/value --
+{
+	$id:    "run"
+	stdout: "foo"
+	env: {
+		input: "foo"
+	}
+}
+-- out/run/t2/stats --
+Leaks:  0
+Freed:  12
+Reused: 12
+Allocs: 0
+Retain: 0
+
+Unifications: 12
+Conjuncts:    20
+Disjuncts:    12
+-- out/run/stats/totals --
+Leaks:  0
+Freed:  23
+Reused: 18
+Allocs: 5
+Retain: 0
+
+Unifications: 23
+Conjuncts:    36
+Disjuncts:    23