prevent invalid scope when parsing bodies containing erroneous decls

[ghost]

Required to fix ... dlang-community/DCD#600

[ghost]

this breaks the arbitrary lookups required by the language.

[WebFreak001]

if parseDeclarationsAndStatements can't return null anymore, I think the following classes/members would never be null anymore:

• CaseStatement.declarationsAndStatement
• CaseRangeStatement.declarationsAndStatement
• DefaultStatement.declarationsAndStatement

BlockStatement.declarationsAndStatement before was null with an error in the content, now it is really only null if it's empty (} following the {)

Because of this PR I also found the following potential null-reference-errors which would be fixed by this:

formatter.d:616 (void format(const CaseRangeStatement caseRangeStatement)) and formatter.d:638 (void format(const CaseStatement caseStatement)) both call formatCaseDecls without null check of declarationsAndStatements and the method itself just accesses members.

formatter.d:1036 (void format(const DefaultStatement defaultStatement)) directly accesses the member without null check

nvm stopping checking this out if it's deleted then

[ghost]

Yeah the formatter bugs are not a surprise, see #346.

[ghost]

@WebFreak001, I have maybe a working fix coming.

[codecov]

Codecov Report

Merging #359 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #359      +/-   ##
==========================================
+ Coverage   74.16%   74.17%   +0.01%     
==========================================
  Files           8        8              
  Lines        6874     6877       +3     
==========================================
+ Hits         5098     5101       +3     
  Misses       1776     1776

Impacted Files	Coverage Δ
src/dparse/parser.d	90.77% <100%> (ø)	⬆️

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[ghost]

Okay it seems to work and doesn't break dparse test suite. This time the approach is more pragmatic. The case that breaks DCD, i.e a syntax error, is exactly detected.

[ghost]

DCD test suite works too now.