[clang-format] Segmentation fault when formatting nested namespaces

[d0nc1h0t]

When formatting this part of the code:

namespace ns1 { namespace ns2 { namespace ns3 {

void func_in_ns() {
    int res{ 0 };
// block for debug mode
#ifndef NDEBUG

#endif
}

}}}

with the following style settings:

---
Language:        Cpp
BasedOnStyle:  LLVM

CompactNamespaces: true
NamespaceIndentation: Inner

clang-format crashes with an error segmentation fault. As I found out, this is due to the overflow of the Level value for the comment line. Overflow occurs in line 393 of the file clang/lib/Format/UnwrappedLineFormatter.cpp:

    ...
            if (!(*CompactedLine)->InPPDirective)
              (*CompactedLine)->Level -= OutdentBy;
    ...

OutdentBy turns out to be greater than the value (*CompactedLine)->Level, which causes an overflow.
I see the following way to solve the problem:

    ...
            if (!(*CompactedLine)->InPPDirective)
              (*CompactedLine)->Level -= std:min(OutdentBy, (*CompactedLine)->Level);
    ...

[llvmbot]

@llvm/issue-subscribers-clang-format

[owenca]

OutdentBy turns out to be greater than the value (*CompactedLine)->Level, which causes an overflow. I see the following way to solve the problem:

    ...
            if (!(*CompactedLine)->InPPDirective)
              (*CompactedLine)->Level -= std:min(OutdentBy, (*CompactedLine)->Level);
    ...

This seems to work. Can you submit a patch at https://reviews.llvm.org?

Tagging @rymiel.

[d0nc1h0t]

Submit patch D158363.