[Issue 22365] Compiler crash: tcs.body_ null in StatementSemanticVisitor.visit(TryCatchStatement) in semantic3 pass (dmd/statementsem.d:3956)

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22365

--- Comment #2 from evilrat666 at gmail.com ---
(In reply to RazvanN from comment #1)
> The chances of this bug getting fixed without a minimal reproducible  test
> case are small. Maybe you can use DustMite [1] to reduce it?
> 
> [1]
> https://dlang.org/blog/2020/04/13/dustmite-the-general-purpose-data-
> reduction-tool/

nope, unfortunately I wasn't able to reduce it yet, this is a complex library
with tons of dependencies and it is happily reduces it down to 'import ;'.

I'll try again later, meanwhile I traced down the issue and ready to submit
possible fix (I hope that's a real fix and not just symptoms mending) PR after
I double check everything.

Here is an overview
-----------------------------------------
dmd issue 22365

calls:

  [1] semantic3.d:1369  Semantic3Visitor.visit(CtorDeclaration) at 1446
TryCatchStatemt generation

  [2] semantic3.d:208  Semantic3Visitor.visit(FuncDeclaration) at 595
statementSemantic(funcdecl.fbody, sc2) call 

  [3] statementsem.d:148  statementSemantic(Statement, Scope*) at 145
StatementSemanticVisitor.accept()

  [4] statement.d:1580  TryCatchStatemt.accept (just in case)

  [5] statementsem.d:3936  StatementSemanticVisitor.visit(TryCatchStatemt) at
3957 semanticScope() <--- here, returns wrong scope

    [6] statementsem.d:4486  semanticScope(Statement, Scope*, Statement,
Statement, Statement) <--- push & pop the same scope?

    [7] statementsem.d:4473  semanticNoScope(Statement, Scope*) at 4468
statementSemantic() returns null which triggers assert above

        [8] statementsem.d:236  StatementSemanticVisitor.visit(CompoundStatent)
at 257-264 flatten() and then statementSemantic()

          [9] statementsem.d:4631  flatten(Statement, Scope*)  probably at 4720
if condition


specifically look: 

[5]
https://github.com/dlang/dmd/blob/96b959e27c690f5e3abf411f8032c60f4728c1c1/src/dmd/statementsem.d#L3936

[6]
https://github.com/dlang/dmd/blob/96b959e27c690f5e3abf411f8032c60f4728c1c1/src/dmd/statementsem.d#L4497

so, at step 6 when using debbuger after semanticNoScope() restore s (null at
this moment) back to original s (from function argument), now it works as
expected

        > s = s.semanticNoScope(scd); // <- null
        > /* restore s */
    > scd.pop(); 
    > return s;

tracing it further...

[8]
https://github.com/dlang/dmd/blob/96b959e27c690f5e3abf411f8032c60f4728c1c1/src/dmd/statementsem.d#L255

calling flatten() produces Statements[] array with single null element which is
then returned as valid result here around line 420

    > if (cs.statements.length == 1)
    > {
    >   result = (*cs.statements)[0];
    >   return;
    > }

[9]
https://github.com/dlang/dmd/blob/96b959e27c690f5e3abf411f8032c60f4728c1c1/src/dmd/statementsem.d#L4726

debug condition doesn't get picked up and returns that Statements[] array with
single null element afterwards

    > if (cs.condition.include(sc))

can be fixed with adding else if check for null and else return 0 here 
https://github.com/dlang/dmd/blob/96b959e27c690f5e3abf411f8032c60f4728c1c1/src/dmd/statementsem.d#L4737



this doesn't happens when adding debug else condition to original problem
source, or replacing debug with version (all/none) or anything else, so there
is a logic issue related to debug ConditionStatement somewhere

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