ci: Test minimum cmake version in olddeps job

ci/configs/olddeps.bash

@@ -1,5 +1,5 @@
-CI_DESC="CI job using old Cap'n Proto version"
+CI_DESC="CI job using old Cap'n Proto and cmake versions"
 CI_DIR=build-olddeps
 export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Wno-error=array-bounds"
-NIX_ARGS=(--argstr capnprotoVersion "0.7.1")
+NIX_ARGS=(--argstr capnprotoVersion "0.7.1" --argstr cmakeVersion "3.12.4")
 BUILD_ARGS=(-k)

ci/scripts/ci.sh

@@ -18,7 +18,20 @@ fi
 [ -n "${CI_CLEAN-}" ] && rm -rf "${CI_DIR}"
 
 cmake --version
+cmake_ver=$(cmake --version | awk '/version/{print $3; exit}')
+ver_ge() { [ "$(printf '%s\n' "$2" "$1" | sort -V | head -n1)" = "$2" ]; }
 
-cmake -B "$CI_DIR" "${CMAKE_ARGS[@]+"${CMAKE_ARGS[@]}"}"
-cmake --build "$CI_DIR" -t "${BUILD_TARGETS[@]}" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
-ctest --test-dir "$CI_DIR" --output-on-failure
+src_dir=$PWD
+mkdir -p "$CI_DIR"
+cd "$CI_DIR"
+cmake "$src_dir" "${CMAKE_ARGS[@]+"${CMAKE_ARGS[@]}"}"
+if ver_ge "$cmake_ver" "3.15"; then
+  cmake --build . -t "${BUILD_TARGETS[@]}" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
+else
+  # Older versions of cmake can only build one target at a time with --target,
+  # and do not support -t shortcut
+  for t in "${BUILD_TARGETS[@]}"; do
+    cmake --build . --target "$t" -- "${BUILD_ARGS[@]+"${BUILD_ARGS[@]}"}"
+  done
+fi
+ctest --output-on-failure

shell.nix

@@ -3,6 +3,7 @@
 , enableLibcxx ? false # Whether to use libc++ toolchain and libraries instead of libstdc++
 , minimal ? false # Whether to create minimal shell without extra tools (faster when cross compiling)
 , capnprotoVersion ? null
+, cmakeVersion ? null
 }:
 
 let
@@ -37,12 +38,23 @@ let
   capnproto = capnprotoBase.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
   clang = if enableLibcxx then llvm.libcxxClang else llvm.clang;
   clang-tools = llvm.clang-tools.override { inherit enableLibcxx; };
+  cmakeHashes = {
+    "3.12.4" = "sha256-UlVYS/0EPrcXViz/iULUcvHA5GecSUHYS6raqbKOMZQ=";
+  };
+  cmakeBuild = if cmakeVersion == null then pkgs.cmake else (pkgs.cmake.overrideAttrs (old: {
+    version = cmakeVersion;
+    src = pkgs.fetchurl {
+      url = "https://cmake.org/files/v${lib.versions.majorMinor cmakeVersion}/cmake-${cmakeVersion}.tar.gz";
+      hash = lib.attrByPath [cmakeVersion] "" cmakeHashes;
+    };
+    patches = [];
+  })).override { isMinimalBuild = true; };
 in crossPkgs.mkShell {
   buildInputs = [
     capnproto
   ];
   nativeBuildInputs = with pkgs; [
-    cmake
+    cmakeBuild
     include-what-you-use
     ninja
   ] ++ lib.optionals (!minimal) [