Allow empty target properties block

[oowekyala]

This is especially handy when you comment out a target property. For now if the block happens to be empty you get a really unfriendly parsing error:

lfc: error: no viable alternative at input '}'
--> ../sandbox/R.lf:3:1
  |
2 |  // timeout: 3 sec
3 | };
  | ^^ no viable alternative at input '}'
  |
4 | main reactor R(p: int(2)) {

lfc: error: missing '}' at ';'
--> ../sandbox/R.lf:3:2
  |
2 |  // timeout: 3 sec
3 | };
  |  ^^ missing '}' at ';'
  |
4 | main reactor R(p: int(2)) {

lfc: fatal error: Aborting due to 2 previous errors

With this change, this produces no error anymore. If there is a need to produce an error (which here, I don't think there is) it should be produced by the validator instead.

Note that this also allows empty dictionary values, eg

target C {
   clock-sync-options: { /* everything defaulted */ }
}

I think this is fine for the same reasons (commenting out bindings).

I think it would be nice to make arrays in target properties accept empty arrays too. But this would require that the value of target properties be checked more thoroughly, so I'm leaving this for later.

---

Note: this branch is also merged in the PR #488

[cmnrd]

This was bugging me as well, but I never got to opening an issue or fixing it. Thanks!

I think we should be aware that this grammar rule also allows target Foo { , }, but this is probably fine.

[codecov]

Codecov Report

Merging #551 (ce66faf) into master (4a3b8cd) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #551      +/-   ##
============================================
+ Coverage     66.36%   66.39%   +0.02%     
- Complexity     3462     3465       +3     
============================================
  Files           132      132              
  Lines         22294    22321      +27     
  Branches       2883     2886       +3     
============================================
+ Hits          14795    14819      +24     
- Misses         6352     6354       +2     
- Partials       1147     1148       +1     

Impacted Files	Coverage Δ
org.lflang/xtend-gen/org/lflang/TargetConfig.java	100.00% <0.00%> (ø)
org.lflang/src/org/lflang/TargetProperty.java	85.75% <0.00%> (+0.03%)	⬆️
.../xtend-gen/org/lflang/generator/GeneratorBase.java	56.67% <0.00%> (+0.93%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4a3b8cd...ce66faf. Read the comment docs.

[Soroosh129]

Thanks for fixing this rather annoying issue.

[lhstrh]

This is a good idea! I left a suggestion for improvement.

[lhstrh]

Awesome! Let's merge this.