MingW64 doesn't generate complete debugging information for lambda

I am working on a debugger that supports range of debugging information formats, including DWARF. Recently I've experienced strange thing: mingw64 doesn't emit information about line numbers for code inside lambdas.

Here what I compiled:

void CallLambda(void (*lambda)());

int main()
{
    for (int i = 0; i < 10000; i++)
        CallLambda([]()-> void        // <-- line #27
        {
            CallLambda([]()-> void
            {
                new int;
                new int;
            });
        });

    return 0;
}
...
void CallLambda(void (*lambda)())
{
    lambda(); // <-- line #138
}

My debugger hooks calls of operator new and saves call stack for each; addresses only. Later entries are resolved using available debugging information.

Here the call stacks I got for those operator new:

libstdc++-6.dll!Znwy + 0x17 bytes 000000006fd07287
main.exe!0000000000401571 (for another new int here the address main.exe!000000000040157b)
main.exe!0000000000401594
main.exe!_Z10CallLambdaPFvvE Line 138 + 0x10 bytes 00000000004019f8
main.exe!00000000004015cd
main.exe!00000000004015e6
main.exe!_Z10CallLambdaPFvvE Line 138 + 0x10 bytes 00000000004019f8
main.exe!main Line 25 + 0x2c bytes 000000000040162f
...

I dumped the DWARF debugging information to find any information for addresses 0x401571 and 0x40157b.

Found the only place that corresponds to both addresses:

< 4><0x00005b48>          DW_TAG_structure_type
                            DW_AT_name                  <lambda()>
                            DW_AT_decl_file             0x00000001 I:/Projects/deleaker/branches/branch_2020_02_10_leak_in_lambda/deleaker2/TestProjects/MingwTest/main.cpp
                            DW_AT_decl_line             0x0000001b
...
< 5><0x00005b6e>            DW_TAG_subprogram
...
                              DW_AT_low_pc                0x00401560
                              DW_AT_high_pc               <offset-from-lowpc>39

Here the entire output.

So it seems that the information is not enough to locate line numbers for 0x401571 and 0x40157b: parent node DW_TAG_structure_type contains DW_AT_decl_line = 0x0000001b = 27.

I believe I missed something.

Here the mingw64 version:

g++.EXE (i686-posix-dwarf-rev0, Built by MinGW-W64 project) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
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