remove leading and trailing empty lines in a block

[flan6]

This pull request is intended to achieve what was discussed on issue #284 leaving empty trailing lines in a block if it is followed by an else-if statement, otherwise removes it. Also takes over (somewhat) PR #286.

@mvdan please feel free to suggest any change you see suitable.

close #284

[bshelton]

LGTM, what are we waiting on here?

[mvdan]

Thanks for the patch and apologies for the slow response.

The code change looks fine. I also ran the updated gofumpt on a number of my projects and it mostly looks good, except in two cases.

First, if-elses still remove the trailing empty line, because your code only opts out for if-elseif. I think that needs to be adjusted so that the empty line below is not removed:

    meta := s.MetadataGraph()
    var rdeps map[PackageID]*metadata.Package
    if transitive {
        rdeps = meta.ReverseReflexiveTransitiveClosure(id)
 
        // Remove the original package ID from the map.
        // (Callers all want irreflexivity but it's easier
        // to compute reflexively then subtract.)
        delete(rdeps, id)
-
    } else {
        // direct reverse dependencies
        rdeps = make(map[PackageID]*metadata.Package)
        for _, rdepID := range meta.ImportedBy[id] {
            if rdep := meta.Packages[rdepID]; rdep != nil {
                rdeps[rdepID] = rdep
            }
        }
    }

Second, I wonder whether this change is a good idea or not:

    switch tok {
-
    case token.FOR, token.IF:
        if rhs {
            expr = p.parseExpr()
            break
        }
        comp, ident := p.parseComprehension()
        if comp != nil {
            return nil, nil, comp, false
        }
        expr = ident
 
    case token.LET:
        let, ident := p.parseLetDecl()
        if let != nil {
            return nil, nil, let, false
        }
        expr = ident

Note how empty lines are used to separate the switch cases, so a leading empty line does add some symettry. Given how common large switches with many cases are, perhaps we should always allow a leading empty line in a switch as a special case. I don't think it's worth getting into heuristics for them.