[clang] [clang-tools-extra] [clangd] Handle C++20 annot_module_name token and don't discard successfully built modules when on fail (PR #187858)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

interesting, it seems like either you or me made some basic problems, I still can't reproduce the crash in trunk again. Here is my steps:

```
$bin/clangd --version
clangd version 23.0.0git (git at github.com:llvm/llvm-project.git 9085f74018a4f465afa84815d64af850f09b733f)
Features: linux
Platform: x86_64-unknown-linux-gnu

[chuanqi.xcq at i32g15300.sqa.eu95 /home/chuanqi.xcq/llvm-project-for-work/build]
$bin/llvm-lit ../clang-tools-extra/clangd/test/non-exist.test -v
-- Testing: 1 tests, 1 workers --
PASS: Clangd :: non-exist.test (1 of 1)

Testing Time: 0.12s

Total Discovered Tests: 1
  Passed: 1 (100.00%)

[chuanqi.xcq at i32g15300.sqa.eu95 /home/chuanqi.xcq/llvm-project-for-work/build]
$cat ../clang-tools-extra/clangd/test/non-exist.test
#
## reproduce a crash in module processing - seems having a non-existent module imported
## as the last statement in a file causes clangd to crash
## modified from modules.test
#
# Windows have different escaping modes.
# FIXME: We should add one for windows.
# UNSUPPORTED: system-windows
#
# RUN: rm -fr %t
# RUN: mkdir -p %t
# RUN: split-file %s %t
#
# RUN: sed -e "s|DIR|%/t|g" %t/compile_commands.json.tmpl > %t/compile_commands.json.tmp
# RUN: sed -e "s|CLANG_CC|%clang|g" %t/compile_commands.json.tmp > %t/compile_commands.json
# RUN: sed -e "s|DIR|%/t|g" %t/definition.jsonrpc.tmpl > %t/definition.jsonrpc
#
# RUN: clangd -experimental-modules-support -lit-test < %t/definition.jsonrpc

#--- A.cppm
module;
export module A;

#--- Use.cpp
module;
export module Use;
import A;
import NonExistent;

#--- compile_commands.json.tmpl
[
    {
      "directory": "DIR",
      "command": "CLANG_CC -fprebuilt-module-path=DIR -std=c++20 -o DIR/main.cpp.o  DIR/Use.cpp  -fmodule-file=A=DIR/A.pcm",
      "file": "DIR/Use.cpp",
      "output": "DIR/main.cpp.o"
    },
    {
      "directory": "DIR",
      "command": "CLANG_CC -fprebuilt-module-path=DIR --std=c++20 DIR/A.cppm --precompile -o DIR/A.pcm",
      "file": "DIR/A.cppm",
      "output": "DIR/A.pcm"
    }
]

#--- definition.jsonrpc.tmpl
{
  "jsonrpc": "2.0",
  "id": 0,
  "method": "initialize",
  "params": {
    "processId": 123,
    "rootPath": "clangd",
    "capabilities": {
      "textDocument": {
        "completion": {
          "completionItem": {
            "snippetSupport": true
          }
        }
      }
    },
    "trace": "off"
  }
}
---
{
  "jsonrpc": "2.0",
  "method": "textDocument/didOpen",
  "params": {
    "textDocument": {
      "uri": "file://DIR/Use.cpp",
      "languageId": "cpp",
      "version": 1,
      "text": "module;\nexport module Use;\nimport A;\nimport NonExistent;\n"
    }
  }
}
---
{"jsonrpc":"2.0","id":2,"method":"shutdown"}
---
{"jsonrpc":"2.0","method":"exit"}

```

https://github.com/llvm/llvm-project/pull/187858