Add singleConfig/multiConfig object form for cmake.buildDirectory

[Copilot]

This change addresses item #2426

This changes visible behavior

The following changes are proposed:

• Allow cmake.buildDirectory to accept an object with singleConfig and/or multiConfig properties, selecting the appropriate template based on the active generator type
• Pass isMultiConfFast from the CMake driver to the config reader for branch resolution
• Check both branches in checkBuildDirectories duplicate-directory warning (generator unknown at that point)
• Add unit tests covering string form, object form, fallbacks, and defaults

The purpose of this change

Single-config generators (Make, Ninja) typically need ${buildType} in the build path to separate configurations; multi-config generators (Visual Studio, Ninja Multi-Config, Xcode) don't. Today there's no way to use different cmake.buildDirectory templates per generator type.

New object form alongside the existing string form (fully backward-compatible):

{
  "cmake.buildDirectory": {
    "singleConfig": "${workspaceFolder}/build/${buildKitTargetArch}-${buildType}",
    "multiConfig": "${workspaceFolder}/build/${buildKitTargetArch}"
  }
}

If only one key is provided, the other falls back to it. If neither is set, falls back to ${workspaceFolder}/build.

Other Notes/Information

Files changed:

• package.json — schema updated to oneOf (string | object with singleConfig/multiConfig)
• package.nls.json — descriptions for the new sub-properties
• src/config.ts — buildDirectory type widened, isMultiConfig?: boolean parameter added to resolution method, defaultBuildDirectoryValue constant extracted
• src/drivers/cmakeDriver.ts — _refreshExpansions() and setKit() now pass this.isMultiConfFast
• src/projectController.ts — checkBuildDirectories() checks both branches of object form
• test/unit-tests/config.test.ts — 8 new tests; fixed a test that was calling buildDirectory(true) which fails in the VS Code test host because isDefaultValue() checks real vscode.workspace.getConfiguration, not internal configData
• CHANGELOG.md — feature entry

No changes needed for CMake Presets mode — binaryDir comes from the preset itself.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature] Add option to specify cmake.buildDirectory for single- and multi-config generators, respectively</issue_title>
<issue_description>## Problem Description

In CMake Generator, there are single- and multi-config generator to choose. If we use single-config, such as MinGW Makefiles, I would like to separate build directories for Configurations and Architectures. Thanks to the Substitution Variable provided by CMake-Tools, we can design our custom build directory.

1. Single-Config Generator

If I use single-config Generator, for example MinGW Makefiles or NMake Makefiles, one Makefile file only supports one configuration. So in order to differentiate Debug and Release configurations, I will set cmake.buildDirectory like this:

{
  "cmake.buildDirectory": 
    "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}-${buildType}"
}

The possible results of build directories will look like this:

build/
    win32-MSVC-x64-Debug/
    win32-MSVC-x64-Release/
    win32-MSVC-x86-Debug/
    win32-MSVC-x86-Release/
    win32-GCC-x86-Debug/
    win32-GCC-x86-Release/
    win32-GCC-x86-MinSizeRel/

2. Multi-Config Generator

However, if I choose to use multi-config generators such as Ninja Multi-Config, it is a waste to separate different configurations into individual sub-folders. So I will delete ${buildType} variable from the single-config format. Here is my format of cmake.buildDirectory:

{
  "cmake.buildDirectory": 
    "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}"
}

The possible results of build directories will look like:

build/
    win32-MSVC-x64/
    win32-MSVC-x86/
    win32-GCC-x64/
    win32-GCC-x86/

Expected Setting

I hope CMake-Tools can give us an option to set cmake.buildDirectory for single-config and multi-config, respectively. And Then CMake-Tools will auto-detect which type our currently-used generator belongs to, single-config or multi-config.

For example:

{
  "cmake.buildDirectory": {
    "singleConfig": "${workspaceFolder}/build",
    "multiConfig": "${workspaceFolder}/build",
  }
}

Of course, we can still retain the original format of cmake.buildDirectory. That means both single- and multi-config will use the same format of cmake.buildDirectory:

{
  "cmake.buildDirectory": "${workspaceFolder}/build/${buildKitHostOs}_${buildKitTargetOs}"
}

In my case, I would like to set this settings like this:

{
  "cmake.buildDirectory": {
    "singleConfig": 
      "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}-${buildType}",
    "multiConfig": 
      "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}"
  }
}

Platform and Version:

• Visual Studio Code Version: 1.65.2
• CMake Tools Version: 1.9.2
• CMake Version: 3.21.2</issue_description>

<agent_instructions>## Feature: Add per-generator-type cmake.buildDirectory support (single-config vs. multi-config)

Background

Issue: #2426 - #2426

Single-config generators (e.g. MinGW Makefiles, NMake Makefiles, Unix Makefiles) require a separate build directory per build type, so users typically include ${buildType} in cmake.buildDirectory.
Multi-config generators (Ninja Multi-Config, Visual Studio, Xcode) manage all configurations in one
directory, making ${buildType} wasteful.

Today there is no way to specify different cmake.buildDirectory values for the two cases. The request is
to allow an object form alongside the existing string form:

{
  "cmake.buildDirectory": {
    "singleConfig": "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}-${buildType}",
    "multiConfig":  "${workspaceFolder}/build/${buildKitTargetOs}-${buildKitVendor}-${buildKitTargetArch}"
  }
}

The existing plain-string form must continue to work — this is a purely additive change.

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What to change — starting points only, explore freely

1. package.json — schema

cmake.buildDirectory is currently declared as a "type": "string". Change it to accept either a string
or an object with optional singleConfig / multiConfig string properties (use oneOf). Add a clear markdownDescription that explains when each form is chosen. Follow the style of nearby settings.

2. src/config.ts — type + reader

• In ExtensionConfigurationSettings, change the buildDirectory field from string to
  ...

• Fixes [Feature] Add option to specify cmake.buildDirectory for single- and multi-config generators, respectively #2426

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