https://issues.dlang.org/show_bug.cgi?id=21398

          Issue ID: 21398
           Summary: DMD segfaults during AST visit
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: solarliner@gmail.com

Created attachment 1810
  --> https://issues.dlang.org/attachment.cgi?id=1810&action=edit
segfault repro

Hi,

DMD has been acting up on this piece of code I have attached as reproduction.

If, within main (in `app.d`), there is no reference to the custom types, then compilation and execution are fine. However as soon as I introduce one of the types I defined in `mem.d`, the compiler segfaults.

I've caught a backtrace in gdb:

    #0  0x00005555557a1421 in
_D3dmd6hdrgen13visitWithMaskFCQBc5mtype4TypehPSQBt4root9outbuffer9OutBufferPSQCxQCw11HdrGenStateZv
()
    #1  0x00005555557a173b in
_D3dmd6hdrgen13typeToBufferxFCQBc5mtype4TypePSQBs4root9outbuffer9OutBufferPSQCwQCv11HdrGenStateZv
()
    #2  0x00005555556914f3 in Type::toChars() const ()
    #3  0x00005555557bed49 in ExpressionSemanticVisitor::visit(CallExp*) ()
    #4  0x00005555556f2e4c in StatementSemanticVisitor::visit(ExpStatement*) ()
    #5  0x00005555556f383a in
StatementSemanticVisitor::visit(CompoundStatement*) ()
    #6  0x00005555556f4caf in StatementSemanticVisitor::visit(ScopeStatement*)
()
    #7  0x00005555556f5fab in
_D3dmd12statementsem15semanticNoScopeFCQBl9statement9StatementPSQCk6dscope5ScopeZQBr
()
    #8  0x00005555557028b3 in StatementSemanticVisitor::visit(IfStatement*) ()
    #9  0x00005555556f383a in
StatementSemanticVisitor::visit(CompoundStatement*) ()
    #10 0x000055555571e3bb in Semantic3Visitor::visit(FuncDeclaration*) ()
    #11 0x00005555557276ba in Semantic3Visitor::visit(AggregateDeclaration*) ()
    #12 0x000055555571c0e1 in Semantic3Visitor::visit(TemplateInstance*) ()
    #13 0x00005555557fe0d8 in
_D3dmd10dsymbolsem24templateInstanceSemanticFCQBs9dtemplate16TemplateInstancePSQCz6dscope5ScopePSQDr4root5array__T5ArrayTCQEq10expression10ExpressionZQBkZv
()
    #14 0x00005555557b6fe4 in ExpressionSemanticVisitor::visit(ScopeExp*) ()
    #15 0x00005555557be6c4 in ExpressionSemanticVisitor::visit(CallExp*) ()
    #16 0x00005555557959c7 in
_D3dmd7initsem9inferTypeFCQy4init11InitializerPSQBu6dscope5ScopeZ8visitExpMFCQCxQCa14ExpInitializerZQCx
()
    #17 0x00005555557955bd in
_D3dmd7initsem9inferTypeFCQy4init11InitializerPSQBu6dscope5ScopeZQBo ()
    #18 0x000055555580c5fd in DsymbolSemanticVisitor::visit(VarDeclaration*) ()
    #19 0x00005555557c1be1 in ExpressionSemanticVisitor::visit(DeclarationExp*)
()
    #20 0x00005555556f2e4c in StatementSemanticVisitor::visit(ExpStatement*) ()
    #21 0x00005555556f383a in
StatementSemanticVisitor::visit(CompoundStatement*) ()
    #22 0x000055555571e3bb in Semantic3Visitor::visit(FuncDeclaration*) ()
    #23 0x000055555571c841 in Semantic3Visitor::visit(Module*) ()
    #24 0x000055555576e380 in _D3dmd4mars7tryMainFmPPxaKSQz7globals5ParamZi ()
    #25 0x000055555577889f in D main ()

As I am new with D, the code I wrote may not be correct, however I don't think compilers are supposed to find code so ugly they crash, lol.

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