Merge and/or Override flags of different configure presets in CMakePresets.json

Question

I have two configure presets in my CMakePresets.json were I would like to merge the flags of the inherit configurePresets (gcc) with the other preset (gcc-arm-embedded)

Here is a simplified version:

  "configurePresets": [
    {
      "name": "gcc",
      "hidden": true,
      "cacheVariables": {
        "CMAKE_CXX_FLAGS": "-Wall -Wextra",
        "CMAKE_BUILD_TYPE": "Release"
      }
    },
    {
      "name": "gcc-arm-embedded",
      "hidden": true,
      "inherits": ["gcc"],
      "cacheVariables": {
        "CMAKE_CXX_FLAGS": "-ffunction-sections -fdata-sections",
        "CMAKE_EXE_LINKER_FLAGS": "-mcpu=cortex-m7 -mthumb",
        "CMAKE_BUILD_TYPE": "MinSizeRel"
      }
    },
    {
      "name": "embedded",
      "inherits": ["gcc", "gcc-arm-embedded"]
    }
  ]

The problem is, if I use the presets embedded the resulting CMAKE flags are:

CMAKE_CXX_FLAGS: "-Wall -Wextra"
CMAKE_EXE_LINKER_FLAGS: "-mcpu=cortex-m7 -mthumb",
CMAKE_BUILD_TYPE: "Release"

My goal is this:

CMAKE_CXX_FLAGS: "-Wall -Wextra -ffunction-sections -fdata-sections"
CMAKE_EXE_LINKER_FLAGS: "-mcpu=cortex-m7 -mthumb",
CMAKE_BUILD_TYPE: "MinSizeRel"

Is this somehow possible with CMakePresets?

I would _love_ this to be a standard feature – Alex Reinking Jan 20 '22 at 18:50 — Alex Reinking, Jan 20 '22 at 18:50

score 6 · Accepted Answer · answered Jan 20 '22 at 19:02

First, simplify the inherits entry to:

"inherits": ["gcc-arm-embedded"]

The resolution order works left to right, never overwriting, but since gcc-arm-embedded inherits from gcc already, there's no need to specify both. So that gets you to this:

CMAKE_CXX_FLAGS: "-ffunction-sections -fdata-sections"
CMAKE_EXE_LINKER_FLAGS: "-mcpu=cortex-m7 -mthumb",
CMAKE_BUILD_TYPE: "MinSizeRel"

Now let's add a base preset:

    {
      "name": "base",
      "hidden": true,
      "cacheVariables": {
        "CMAKE_CXX_FLAGS": "$env{CXX_WARNINGS} $env{CXX_OPT}",
        "CMAKE_BUILD_TYPE": "Release"
      }
    },

Then make gcc inherit from base and remove the cacheVariables section. Instead, set:

      "environment": {
        "CXX_WARNINGS": "-Wall -pedantic"
      }

and in gcc-arm-embedded additionally set:

      "environment": {
        "CXX_OPT": "-ffunction-sections -fdata-sections"
      }

The end result is this:

{
  "version": 3,
  "cmakeMinimumRequired": {
    "major": 3,
    "minor": 21,
    "patch": 0
  },
  "configurePresets": [
    {
      "name": "base",
      "hidden": true,
      "cacheVariables": {
        "CMAKE_CXX_FLAGS": "$env{CXX_WARNINGS} $env{CXX_OPT}",
        "CMAKE_BUILD_TYPE": "Release"
      }
    },
    {
      "name": "gcc",
      "inherits": ["base"],
      "hidden": true,
      "environment": {
        "CXX_WARNINGS": "-Wall -pedantic"
      }
    },
    {
      "name": "gcc-arm-embedded",
      "hidden": true,
      "inherits": ["gcc"],
      "cacheVariables": {
        "CMAKE_EXE_LINKER_FLAGS": "-mcpu=cortex-m7 -mthumb",
        "CMAKE_BUILD_TYPE": "MinSizeRel"
      },
      "environment": {
        "CXX_OPT": "-ffunction-sections -fdata-sections"
      }
    },
    {
      "name": "embedded",
      "inherits": ["gcc-arm-embedded"]
    }
  ]
}

@Viatorus - You're welcome! And it is for now... I'm hoping they'll add some "merging" inheritance modes down the line so we don't have to do this dance (and pollute the environment!). — Alex Reinking, Jan 20 '22 at 23:34

Merge and/or Override flags of different configure presets in CMakePresets.json

1 Answers1