LLDB DAP assertion failure

[sedymrak]

I am using VSCode IDE.
Until recently, I was using codelldb VSCode extension for debugging C++ code.
Now I am experimenting with "LLDB DAP" VSCode extension.
I have compiled lldb with debugging symbols so that I can debug it in VSCode (using the "LLDB DAP" VSCode extension).
I have noticed that whenever the control flow enters the ValueObject::GetExpressionPath method (defined in the lldb/source/ValueObject/ValueObject.cpp file), as soon as I start typing something in the "DEBUG CONSOLE" (it does not matter what), the following error appears in the "DEBUG CONSOLE":

lldb-dap: /home/me/git/other/llvm-project/main/0/clang/lib/Sema/SemaAccess.cpp:750: AccessResult HasAccess(Sema &, const EffectiveContext &, const CXXRecordDecl *, AccessSpecifier, const AccessTarget &): Assertion `Access == AS_private || Access == AS_protected' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /home/me/git/other/llvm-project/main/0/build--main--Debug--mold--make/bin/lldb-dap

and the following message appears in the "LLDB-DAP" console (accessible via the combo-box in the "OUTPUT" pane:

2025-12-11 22:30:49.196 [error] Error: read error
	at Socket.<anonymous> (file:///usr/share/code/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:132:1948)
	at Socket.emit (node:events:531:35)
	at Pipe.<anonymous> (node:net:346:12)

Afterwards, the "DEBUG CONSOLE" is unresponsive.

I have configured VSCode to use lldb-dap built from the main branch by adding the following entry:

"lldb-dap.executable-path": "/home/me/git/other/llvm-project/main/1/build--main--Release--ld--make/bin/lldb-dap",

to the corresponding .vscode/settings.json file.

I suspect that the bug is in the "LLDB DAP" VSCode extension and not in the lldb-dap program.
This suspicion is based on my experiment where I sent and received DAP messages directly to/from the lldb-dap program. I have instructed it to stop in the ValueObject::GetExpressionPath method and when the control flow reached that method, the lldb-dap remained responsive in the usual way.

[llvmbot]

@llvm/issue-subscribers-lldb-dap

Author: Matej Košík (sedymrak)

I am using VSCode IDE. Until recently, I was using `codelldb` VSCode extension for debugging C++ code. Now I am experimenting with "LLDB DAP" VSCode extension. I have compiled `lldb` with debugging symbols so that I can debug it in VSCode (using the "LLDB DAP" VSCode extension). I have noticed that whenever the control flow enters the `ValueObject::GetExpressionPath` method (defined in the `lldb/source/ValueObject/ValueObject.cpp` file), as soon as I start typing something in the "DEBUG CONSOLE" (it does not matter what), the following error appears in the "DEBUG CONSOLE": ``` lldb-dap: /home/me/git/other/llvm-project/main/0/clang/lib/Sema/SemaAccess.cpp:750: AccessResult HasAccess(Sema &, const EffectiveContext &, const CXXRecordDecl *, AccessSpecifier, const AccessTarget &): Assertion `Access == AS_private || Access == AS_protected' failed. PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace. Stack dump: 0. Program arguments: /home/me/git/other/llvm-project/main/0/build--main--Debug--mold--make/bin/lldb-dap ``` and the following message appears in the "LLDB-DAP" console (accessible via the combo-box in the "OUTPUT" pane: ``` 2025-12-11 22:30:49.196 [error] Error: read error at Socket.<anonymous> (file:///usr/share/code/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:132:1948) at Socket.emit (node:events:531:35) at Pipe.<anonymous> (node:net:346:12) ``` Afterwards, the "DEBUG CONSOLE" is unresponsive.

I have configured VSCode to use lldb-dap built from the main branch by adding the following entry:

"lldb-dap.executable-path": "/home/me/git/other/llvm-project/main/1/build--main--Release--ld--make/bin/lldb-dap",

to the corresponding .vscode/settings.json file.

I suspect that the bug is in the "LLDB DAP" VSCode extension and not in the lldb-dap program.
This suspicion is based on my experiment where I sent and received DAP messages directly to/from the lldb-dap program. I have instructed it to stop in the ValueObject::GetExpressionPath method and when the control flow reached that method, the lldb-dap remained responsive in the usual way.

[ashgti]

Does this also happen if you build and run lldb in the CLI and try to autocomplete a e <variable>?

[sedymrak]

If I have a following C program:

int main() {
  int foo[2][3][4];

  foo[0][0][0] = 1;
  foo[0][0][1] = 2;
  foo[0][0][2] = 3;
  foo[0][0][3] = 4;
  foo[0][1][0] = 11;
  foo[0][1][1] = 12;
  foo[0][1][2] = 13;
  foo[0][1][3] = 14;
  foo[0][2][0] = 21;
  foo[0][2][1] = 22;
  foo[0][2][2] = 23;
  foo[0][2][3] = 24;
  foo[1][0][0] = 101;
  foo[1][0][1] = 102;
  foo[1][0][2] = 103;
  foo[1][0][3] = 104;
  foo[1][1][0] = 111;
  foo[1][1][1] = 112;
  foo[1][1][2] = 113;
  foo[1][1][3] = 114;
  foo[1][2][0] = 121;
  foo[1][2][1] = 122;
  foo[1][2][2] = 123;
  foo[1][2][3] = 124;

  int (*bar)[3][4] = foo;
  int (*baz)[4] = bar[0];

  write(1, "DEBUG/0\n", 8);
  return 0;
}

the following .lldbinit file:

target create ./main
breakpoint set --file main.c --line 32
process launch
script lldb.frame.FindVariable("bar").GetChildAtIndex(0).get_expr_path()

and start LLDB (built from the main branch in the following way:

~/git/other/llvm-project/main/0/install--main--Release--ld--make/bin/lldb --source .lldbinit

then I was not able to observe any problems with the autocompletion of variables that follow the expression LLDB command:

Executing commands in '/home/me/Documents/computer/software/compiler/llvm/github/pull-requests/2025-12-09-fix-ValueObject-GetExpressionPath-met
hod/.lldbinit'.
(lldb) target create ./main
Current executable set to '/home/me/Documents/computer/software/compiler/llvm/github/pull-requests/2025-12-09-fix-ValueObject-GetExpressionPath
-method/main' (x86_64).
(lldb) breakpoint set --file main.c --line 32
Breakpoint 1: where = main`main + 192 at main.c:32:3, address = 0x00000000000011f9
(lldb) process launch
Process 1550012 launched: '/home/me/Documents/computer/software/compiler/llvm/github/pull-requests/2025-12-09-fix-ValueObject-GetExpressionPath
-method/main' (x86_64)
Process 1550012 stopped
* thread #1, name = 'main', stop reason = breakpoint 1.1
    frame #0: 0x00005555555551f9 main`main at main.c:32:3
(lldb) script lldb.frame.FindVariable("bar").GetChildAtIndex(0).get_expr_path()
'bar[0][0]'
(lldb) e f
Available completions:
        foo   -- int (&)[2][3][4]
        float
(lldb) e foo 
(int[2][3][4]) $0 = {
  [0] = {
    [0] = ([0] = 1, [1] = 2, [2] = 3, [3] = 4)
    [1] = ([0] = 11, [1] = 12, [2] = 13, [3] = 14)
    [2] = ([0] = 21, [1] = 22, [2] = 23, [3] = 24)
  }
  [1] = {
    [0] = ([0] = 101, [1] = 102, [2] = 103, [3] = 104)
    [1] = ([0] = 111, [1] = 112, [2] = 113, [3] = 114)
    [2] = ([0] = 121, [1] = 122, [2] = 123, [3] = 124)
  }
}
(lldb) e b
Available completions:
        bar  -- int (*&)[3][4]
        baz  -- int (*&)[4]
        bool
(lldb) e b
Available completions:
        bar  -- int (*&)[3][4]
        baz  -- int (*&)[4]
        bool
(lldb) e ba
Available completions:
        bar -- int (*&)[3][4]
        baz -- int (*&)[4]
(lldb) e ba
Available completions:
        bar -- int (*&)[3][4]
        baz -- int (*&)[4]
(lldb) e bar
(int (*)[3][4]) $1 = 0x00007fffffffd800

[sedymrak]

That, however, is not surprising. I think that the unexpected behavior can only be reproduced when using the "LLDB DAP" VSCode plugin.