CTAD for std::span with a range argument fails

[marralesfios]

Environment

• OS and Version: Arch Linux, kernel 7.0.8.arch1-1
• VS Code Version: 1.120.0, Commit: 0958016b2af9f09bb4257e0df4a95e2f90590f9f
• C/C++ Extension Version: 1.32.2

Bug Summary and Steps to Reproduce

Bug Summary:
When x is a range (e.g. std::string), std::span{x} fails static analysis, despite the code being accepted by both gcc and clang.

Steps to reproduce:

1. Create a new folder
2. copy test.cpp inside
3. open the folder then the file
4. See error

Expected behavior:
No error, std::span<char> is deduced.

Configuration and Logs

c_cpp_properties.json: none needed.
language server logging: see attachment below.

C/C++: Log Diagnostics output:

-------- Diagnostics - 5/18/2026, 3:26:00 PM
Version: 1.32.2
Current Configuration:
{
    "name": "Linux",
    "includePath": [
        "/home/marr-ales-fios/include"
    ],
    "defines": [],
    "intelliSenseMode": "linux-clang-x64",
    "compilerArgs": [
        "-m64",
        "-freflection"
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    "cStandard": "c23",
    "cppStandard": "c++26",
    "intelliSenseModeIsExplicit": false,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPath": "/usr/bin/g++",
    "compilerPathIsExplicit": true,
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.intelliSenseUpdateDelay": 500,
    "C_Cpp.autocompleteAddParentheses": true,
    "C_Cpp.suggestSnippets": false,
    "C_Cpp.default.includePath": [
        "/home/marr-ales-fios/include"
    ],
    "C_Cpp.default.compilerPath": "/usr/bin/g++",
    "C_Cpp.default.compilerArgs": [
        "-m64",
        "-freflection"
    ],
    "C_Cpp.default.cStandard": "c23",
    "C_Cpp.default.cppStandard": "c++26",
    "C_Cpp.vcFormat.indent.caseLabels": true,
    "C_Cpp.codeAnalysis.updateDelay": 1000,
    "C_Cpp.debugShortcut": false,
    "C_Cpp.intelliSenseMemoryLimit": 6144,
    "C_Cpp.vcpkg.enabled": false,
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.experimentalFeatures": "enabled",
    "C_Cpp.copilotHover": "disabled"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {},
    "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"
}
cpptools version (native): 1.32.2.0
Current database path: /home/marr-ales-fios/.cache/vscode-cpptools/aefb1edb3236c37da9f59a487a5c880c/.browse.VC.db
Translation Unit Mappings:
[ /home/marr-ales-fios/Projects/mre/test.cpp - source TU]:
Translation Unit Configurations:
[ /home/marr-ales-fios/Projects/mre/test.cpp ]
    Process ID: 56841
    Memory Usage: 98 MB
    Compiler Path: /usr/bin/g++
    Include Paths:
        include: /home/marr-ales-fios/include
        system include: /usr/include/c++/16.1.1
        system include: /usr/include/c++/16.1.1/x86_64-pc-linux-gnu
        system include: /usr/include/c++/16.1.1/backward
        system include: /usr/lib/gcc/x86_64-pc-linux-gnu/16.1.1/include
        system include: /usr/local/include
        system include: /usr/include
    Standard Version: c++26
    IntelliSense Mode: linux-gcc-x64
    Other Flags:
        --g++
        --gnu_version=160101
Total Memory Usage: 98 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 66487

Other Extensions

No response

Additional context

Language server logging: lsp.txt

[sean-mcmanus]

So far I don't repro it with g++-15, it might be specific to g++-16.

[sean-mcmanus]

@marralesfios Yeah, it repros specifically with g++16.