Intellisense doesn’t work

[roelandschoukens]

Environment

• OS and Version: macOS 15.5
• VS Code Version: Version: 1.100.2 (Universal)
• C/C++ Extension Version: 1.25.3

Bug Summary and Steps to Reproduce

I’m unable to use Intellisense in our project. It is hard to be more specific — if you work at a normal speed, the only thing it will ever do is showing a tooltip with the text “Loading...” There is nothing that actually works.

If I wait for a minute or so, sometimes I do get a tool tip with the expected information.

The same is true for other actions, like jumping to a definition. It will often eventually jump to the definition but it takes a minute or two.

If I wait for something to work, there will always be lines like this in the C/C++ output (the logging level is set to debug):

Quick info operation failed: FE: 'Compiler exited with error - No IL available'
using Tag Parser for quick info

I think it would be useful to at least figure out how/why the compiler is failing. If a compiler fails (whatever that means), could I capture any error output?

The Intellisense configuration is provided by the Cmake tools extension. The log will contain Custom configurations received: lines, and as far as I can tell those configurations are correct. The problem is not reproducible in a toy example.

Configuration and Logs

.vscode/c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Mac",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "cStandard": "c17",
            "cppStandard": "c++17",
            "intelliSenseMode": "macos-clang-arm64",
            "configurationProvider": "ms-vscode.cmake-tools"
        }
    ],
    "version": 4
}

C/C++ Diagnostics (although I am probably not at liberty to share the entire output)

-------- Diagnostics - 27/05/2025, 17:53:45
Version: 1.25.3
Current Configuration:
{
    "name": "Mac",
    "includePath": [
        "/Volumes/Dev/dev/master-wip/**"
    ],
    "defines": [],
    "cStandard": "c17",
    "cppStandard": "c++17",
    "intelliSenseMode": "macos-clang-arm64",
    "configurationProvider": "ms-vscode.cmake-tools",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "configurationProviderInCppPropertiesJson": "ms-vscode.cmake-tools",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "compilerPath": "/usr/bin/clang++",
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.compilerPath": "/usr/bin/clang++",
    "C_Cpp.default.configurationProvider": "ms-vscode.cmake-tools",
    "C_Cpp.loggingLevel": "Debug"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.glsl.h": "glsl",
        "*.comp.h": "glsl",
        "*.dev.h": "glsl",
        "*.ch": "cuda-cpp",
        "unordered_map": "cpp",
        "array": "cpp",
        "vector": "cpp",
        "__hash_table": "cpp",
        "string": "cpp",
        "__bit_reference": "cpp",
        "__bits": "cpp",
        "__config": "cpp",
        "__debug": "cpp",
        "__errc": "cpp",
        "__locale": "cpp",
        "__mutex_base": "cpp",
        "__node_handle": "cpp",
        "__nullptr": "cpp",
        "__split_buffer": "cpp",
        "__string": "cpp",
        "__threading_support": "cpp",
        "__tree": "cpp",
        "__tuple": "cpp",
        "atomic": "cpp",
        "bitset": "cpp",
        "cctype": "cpp",
        "chrono": "cpp",
        "cinttypes": "cpp",
        "clocale": "cpp",
        "cmath": "cpp",
        "codecvt": "cpp",
        "compare": "cpp",
        "complex": "cpp",
        "concepts": "cpp",
        "condition_variable": "cpp",
        "csignal": "cpp",
        "cstdarg": "cpp",
        "cstddef": "cpp",
        "cstdint": "cpp",
        "cstdio": "cpp",
        "cstdlib": "cpp",
        "cstring": "cpp",
        "ctime": "cpp",
        "cwchar": "cpp",
        "cwctype": "cpp",
        "deque": "cpp",
        "exception": "cpp",
        "coroutine": "cpp",
        "forward_list": "cpp",
        "fstream": "cpp",
        "future": "cpp",
        "initializer_list": "cpp",
        "iomanip": "cpp",
        "ios": "cpp",
        "iosfwd": "cpp",
        "iostream": "cpp",
        "istream": "cpp",
        "limits": "cpp",
        "list": "cpp",
        "locale": "cpp",
        "map": "cpp",
        "memory": "cpp",
        "mutex": "cpp",
        "new": "cpp",
        "numeric": "cpp",
        "optional": "cpp",
        "ostream": "cpp",
        "queue": "cpp",
        "random": "cpp",
        "ratio": "cpp",
        "regex": "cpp",
        "scoped_allocator": "cpp",
        "set": "cpp",
        "sstream": "cpp",
        "stack": "cpp",
        "stdexcept": "cpp",
        "streambuf": "cpp",
        "string_view": "cpp",
        "strstream": "cpp",
        "system_error": "cpp",
        "tuple": "cpp",
        "type_traits": "cpp",
        "typeindex": "cpp",
        "typeinfo": "cpp",
        "unordered_set": "cpp",
        "valarray": "cpp",
        "variant": "cpp",
        "algorithm": "cpp",
        "*.ipp": "cpp",
        "*.inc": "cpp",
        "thread": "cpp",
        "*.mm": "cpp",
        "__verbose_abort": "cpp",
        "charconv": "cpp",
        "shared_mutex": "cpp",
        "span": "cpp",
        "hash_map": "cpp",
        "hash_set": "cpp",
        "__memory": "cpp",
        "any": "cpp",
        "execution": "cpp",
        "csetjmp": "cpp",
        "print": "cpp",
        "source_location": "cpp"
    },
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true
    },
    "filesAutoSaveAfterDelay": true,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
Custom browse configuration: 
{
    "browsePath": [
        ...
    ],
    "compilerPath": "/usr/bin/c++",
    "compilerArgs": [],
    "compilerFragments": [
        "-g -std=c++17 -arch arm64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.sdk -mmacosx-version-min=15.0   -mmacosx-version-min=15.0 -stdlib=libc++",
        "-fvisibility=hidden",
        "-ftree-vectorize",
        "-funroll-loops",
        "-Wall",
        "-Wno-format-zero-length",
        "-Wno-comment",
        "-Wno-parentheses",
        "-Wno-unused-function",
        "-Wno-reorder",
        "-Wno-conversion-null",
        "-Wno-backslash-newline-escape",
        "-g",
        "-O0",
        "-fno-inline",
        "-Wno-register"
    ]
}
cpptools version (native): 1.25.3.0
Current database path: /Users/roeland/Library/Caches/vscode-cpptools/3c993f143b9b80ab3c213d13aa080ebf/.browse.VC.db
Translation Unit Mappings:
...
Translation Unit Configurations:
[ filename....cpp ]
    Process ID: 71144
    Memory Usage: 1413 MB
    Compiler Path: /usr/bin/c++
    Include paths:
        ....
        include: /applications/xcode.app/contents/developer/platforms/macosx.platform/developer/sdks/macosx15.sdk/system/library/frameworks
        framework search path: /Library/Frameworks
        system include: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.sdk/usr/include/c++/v1
        system include: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/16/include
        system include: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.sdk/usr/include
        system include: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
        system framework search path (default): /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.sdk/System/Library/Frameworks
    Defines:
        ...
    Standard Version: c++17
    IntelliSense Mode: macos-clang-arm64
    Other Flags:
        --clang
        --clang_version=170006
Total Memory Usage: 2111 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 113249

Other Extensions

No response

Additional context

No response

[sean-mcmanus]

@roelandschoukens Something is causing an abnormally high 1.4-2 GB memory usage in the IntelliSense process, which could cause a performance impact. Are you able to find a reduced repro or what a minimal repro sample code is? i.e. is IntelliSens working with something like

#include <string>

int main()
{
std::string s;
return 0;
}

[roelandschoukens]

@sean-mcmanus no, it does not happen in all projects and it does not happen in a small example.

If the log says Compiler exited with error, which compiler does it mean, and is it possible to capture output from it?

[sean-mcmanus]

@roelandschoukens Our internal IntelliSense compiler is hitting a non-recoverable parsing error. One potential way to diagnose it is to attempt to generate a preprocessed file without any includes or defines by running something like "g++ -std=c++20 -E -dD <-I and -D for all your include paths and defines, plus any other important flags> > test.out.cpp". That may reveal an earlier location in your TU where it's hitting another root cause parser error. Another alternative is to use Go to Definition on the #include to try to find a header that could be the source of the error, or a binary search of removing code in the TU until the issue stops/starts to repro.

[roelandschoukens]

The issue happens even if the source tree has no edits, so running the compiler manually is just going to succeed.