[clang] [clang-tools-extra] [clang] Improve nested name specifier AST representation (PR #147835)

[David Spickett via cfe-commits]

DavidSpickett wrote:

This has changed the output of lldb's std::string formatter when it's not a valid std::string object:
```
******************** TEST 'lldb-api :: functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py' FAILED ********************
Script:
--
/usr/bin/python3.10 /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./lib --env LLVM_INCLUDE_DIR=/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/include --env LLVM_TOOLS_DIR=/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./bin --arch aarch64 --build-dir /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lldb-test-build.noindex --lldb-module-cache-dir /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./bin/lldb --compiler /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./bin/clang --dsymutil /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./bin --lldb-obj-root /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/tools/lldb --lldb-libs-dir /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/./lib --cmake-build-type Release /home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string -p TestDataFormatterStdString.py
--
Exit Code: 1
<...>
--
Command Output (stderr):
--
<...>
======================================================================
FAIL: test_unavailable_summary_libstdcxx_dwarf (TestDataFormatterStdString.StdStringDataFormatterTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1805, in test_method
    return attrvalue(self)
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py", line 223, in test_unavailable_summary_libstdcxx
    self.do_test_summary_unavailable()
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py", line 213, in do_test_summary_unavailable
    self.assertEqual(summary, "Summary Unavailable", "No summary for bad value")
AssertionError: '(null)' != 'Summary Unavailable'
- (null)
+ Summary Unavailable
 : No summary for bad value
Config=aarch64-/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/bin/clang
======================================================================
FAIL: test_unavailable_summary_libstdcxx_dwo (TestDataFormatterStdString.StdStringDataFormatterTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1805, in test_method
    return attrvalue(self)
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py", line 223, in test_unavailable_summary_libstdcxx
    self.do_test_summary_unavailable()
  File "/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/llvm-project/lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/string/TestDataFormatterStdString.py", line 213, in do_test_summary_unavailable
    self.assertEqual(summary, "Summary Unavailable", "No summary for bad value")
AssertionError: '(null)' != 'Summary Unavailable'
- (null)
+ Summary Unavailable
 : No summary for bad value
Config=aarch64-/home/tcwg-buildbot/worker/lldb-aarch64-ubuntu/build/bin/clang
----------------------------------------------------------------------
Ran 54 tests in 6.052s
```
We create the (not a) std::string like this:
```
std::string *not_a_string = (std::string *)0x0;
```
So in some sense, `(null)` is accurate, but users probably expect to see no summary at all.

This is from Linaro's bot where we only run libstdcxx tests. Libcxx testing seems fine (https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake-matrix/). This could be because the formatter has different behaviour for the two standard libraries.

@Michael137 might know where to look for this problem, in the meantime, I'll do my own digging.

https://github.com/llvm/llvm-project/pull/147835