fix: fail if no stages were found

[ctrlaltf24]

Adds a warning message if act is cannot find any stages to run with the filters provided.

Reproduction:

• run act -j gibberish

Desired behavior: some indication I did something silly
Actual behavior: no output, just exit with success.

As a human who often makes spelling mistakes,
it would be nice if act warned me what I was doing that was silly rather than exiting apparently doing
nothing with no obvious indication
I did something wrong.

Alternative solutions:

• Do nothing, it's the user's fault: True it is, would be nice to give them a hint where to resolve their issue
• Exit with error rather than warn: Reasonable behavior as well, not knowledgeable enough with the code base to know for sure this is enough justification to exit

[ZauberNerd]

I think it would make more sense to return an error from here:

act/pkg/model/planner.go

Lines 331 to 358 in 7ba9f30

	var err error
	// next, build an execution graph
	stages := make([]*Stage, 0)
	for len(jobDependencies) > 0 {
	stage := new(Stage)
	for jID, jDeps := range jobDependencies {
	// make sure all deps are in the graph already
	if listInStages(jDeps, stages...) {
	stage.Runs = append(stage.Runs, &Run{
	Workflow: w,
	JobID: jID,
	})
	delete(jobDependencies, jID)
	}
	}
	if len(stage.Runs) == 0 {
	return nil, fmt.Errorf("unable to build dependency graph for %s (%s)", w.Name, w.File)
	}
	stages = append(stages, stage)
	}
	if len(stages) == 0 && err != nil {
	return nil, err
	}
	return stages, nil
	}

As you can see the err variable is unused, so I'd probably remove it and use the if len(stages) == 0 to return nil, fmt.Errorf("...")

[mergify]

@ctrlaltf24 this pull request has failed checks 🛠

[codecov]

Codecov Report

Merging #1970 (e6a2177) into master (4989f44) will increase coverage by 0.90%.
Report is 227 commits behind head on master.
The diff coverage is 61.98%.

@@            Coverage Diff             @@
##           master    #1970      +/-   ##
==========================================
+ Coverage   61.22%   62.12%   +0.90%     
==========================================
  Files          46       52       +6     
  Lines        7141     8484    +1343     
==========================================
+ Hits         4372     5271     +899     
- Misses       2462     2794     +332     
- Partials      307      419     +112     

Files Changed	Coverage Δ
pkg/common/outbound_ip.go	0.00% <0.00%> (ø)
pkg/container/docker_cli.go	82.23% <ø> (ø)
pkg/container/docker_logger.go	52.08% <ø> (ø)
pkg/container/docker_volume.go	0.00% <0.00%> (ø)
pkg/container/file_collector.go	37.30% <0.00%> (ø)
pkg/container/host_environment.go	0.00% <0.00%> (ø)
...ontainer/linux_container_environment_extensions.go	23.07% <0.00%> (-1.25%)	⬇️
pkg/container/util.go	0.00% <0.00%> (ø)
pkg/exprparser/functions.go	66.32% <0.00%> (-1.04%)	⬇️
pkg/container/docker_run.go	13.45% <6.66%> (-0.13%)	⬇️
... and 29 more

... and 2 files with indirect coverage changes

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