Flow instantiation silently fails when subcomponents have connections but not flow implementations

[smithdtyler]

Summary
When instantiating a system implementation with an end to end flow, the flow does not get generated in the .aaxl2 file if a subcomponent of one of the flow elements has an implementation with connections but not flow implementations.

Expected behavior
OSATE should either generate the end to end flow, or should report an error in the instantiation results dialog.

Actual behavior
Instantiation reports no issues, but the end to end flow is absent from the instance file.

Steps To Reproduce

The model below fails to generate an end to end flow instantiation. Uncomment the flow implementations and the flow appears.

package flowdemo
public
	
	system integration
		
	end integration;
	
	system implementation integration.impl
		subcomponents
			a : system example.impl;
			b : system example.impl;
		connections
			ab : feature a.outy -> b.inny;
		flows
			fab : end to end flow a.fouty -> ab -> b.finny;
	end integration.impl;
	
	system example
		features 
			outy: feature group;
			inny: feature group;
		flows
			fouty: flow source outy;
			finny: flow sink inny;
	end example;
	
	system implementation example.impl
		subcomponents
			a : process ex_proc.impl;
			b : process ex_proc.impl;		
			
		connections
			couty: feature a.outy <-> outy;
			cinny: feature inny -> b.inny;

--		flows
--			fouty: flow source a.fouty-> couty -> outy;
--			finny: flow sink inny -> cinny -> b.finny;
	end example.impl;
	
	process ex_proc
		features
			outy: feature group;
			inny: feature group;
		flows
			fouty: flow source outy;
			finny: flow sink inny;
	end ex_proc;
	
	process implementation ex_proc.impl
	end ex_proc.impl;
	
	
end flowdemo;

Desktop (please complete the following information):

• OSATE Version: 2.11
• Operating System: Windows 10

[lwrage]

Unfortunately, it is surprisingly difficult to add an error message for this case. The flow instantiation code is rather convoluted and should really be rewritten.

[lwrage]

see #2438