Root step added to wrap application build steps

This makes it possible to build specific targets using 'zig build <name>
...' command.

Also includes:
* cmake: add_zig_build now passes a target name to `zig build`. Default
  target name is NAME arg, but can be overridden using ZIG_TARGET_NAME.
* Refactoring changes to zapps/CMakeLists.txt.

Author: coderarjob

cmake/BuildZig.cmake

@@ -1,5 +1,7 @@
 # ==================================================================================================
-# add_zig_build (NAME name
+# add_zig_build (
+#              NAME name
+#              [ZIG_TARGET_NAME <target name>]
 #              SOURCES <source> [<source> ...]
 #              OUTPUT  <zig build output file>    COPY_TO <copy output to this directory>
 #              [OUTPUT <zig build output file>    COPY_TO <copy output to this directory>]
@@ -11,6 +13,14 @@
 # Invokes `zig build` command to build output artifacts. These are then copied to some destination
 # directory. 
 #
+# NAME
+# Name of the CMake target that will be created.
+#
+# ZIG_TARGET_NAME
+# Overrides the default name of the Zig build target that gets passed to `zig build` command. This
+# can also be set to a blank string to invoke `zig build` without any target name. Default is same
+# as the NAME argument.
+#
 # OUTPUT
 # A file that the zig build generates. A matching `COPY_TO <dir>` will copy this file to `<dir>`
 # directory.
@@ -36,7 +46,7 @@
 # Changes to the provided directory before `zig build` is run.
 # ==================================================================================================
 function(add_zig_build)
-    set(oneValueArgs NAME WORKING_DIRECTORY)
+    set(oneValueArgs NAME ZIG_TARGET_NAME WORKING_DIRECTORY)
     set(multiValueArgs OUTPUT COPY_TO DEPENDS SOURCES FLAGS DEFINITIONS)
     set(options)
 
@@ -73,12 +83,16 @@ function(add_zig_build)
     if (NOT ZBUILD_WORKING_DIRECTORY)
         set(ZBUILD_WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR})
     endif()
+
+    if (NOT ZBUILD_ZIG_TARGET_NAME)
+        set(ZBUILD_ZIG_TARGET_NAME ${ZBUILD_NAME})
+    endif()
     # -------------------------------------------------------------------------------------------
     # Command to build the executable and copy to destination folders
     # -------------------------------------------------------------------------------------------
     add_custom_command(
         OUTPUT ${ZBUILD_OUTPUT}
-        COMMAND ${ZIG_EXECUTABLE} build ${ZBUILD_FLAGS} ${ZBUILD_DEFINITIONS}
+        COMMAND ${ZIG_EXECUTABLE} build ${ZBUILD_ZIG_TARGET_NAME} ${ZBUILD_FLAGS} ${ZBUILD_DEFINITIONS}
         DEPENDS ${ZBUILD_SOURCES}
         WORKING_DIRECTORY ${ZBUILD_WORKING_DIRECTORY}
     )

src/apps/zapps/CMakeLists.txt

@@ -1,23 +1,25 @@
 find_package(Zig 0.15.1 EXACT REQUIRED)
 
-set(ZIG_COMMON_SOURCE_FILES
+set(zig_common_source_files
     ${CMAKE_CURRENT_LIST_DIR}/mos_build.zig
 )
 
+set(source_dir ${CMAKE_CURRENT_LIST_DIR}/hello)
+set(name hello)
 add_zig_build(
-    NAME hello
+    NAME ${name}
     SOURCES
-        ${ZIG_COMMON_SOURCE_FILES}
-        ${CMAKE_CURRENT_LIST_DIR}/hello/main.zig
-        ${CMAKE_CURRENT_LIST_DIR}/hello/build.zig
+        ${zig_common_source_files}
+        ${source_dir}/main.zig
+        ${source_dir}/build.zig
     DEPENDS
         cm
         crta
     FLAGS ${MOS_ZIG_BUILD_OPTIONS}
     DEFINITIONS ${MOS_ZIG_BUILD_REQUIRED_DEFINES}
-    OUTPUT ${CMAKE_CURRENT_LIST_DIR}/hello/zig-out/bin/hello     COPY_TO ${MOS_OBJ_DIR}
-    OUTPUT ${CMAKE_CURRENT_LIST_DIR}/hello/zig-out/bin/hello.flt COPY_TO ${MOS_BIN_DIR}
-    WORKING_DIRECTORY ${CMAKE_CURRENT_LIST_DIR}/hello
+    OUTPUT ${source_dir}/zig-out/bin/${name}          COPY_TO ${MOS_OBJ_DIR}
+    OUTPUT ${source_dir}/zig-out/bin/${name}.flt      COPY_TO ${MOS_BIN_DIR}
+    WORKING_DIRECTORY ${source_dir}
 )
 
 add_dependencies(build-all hello)

src/apps/zapps/mos_build.zig

@@ -68,18 +68,26 @@ pub fn addDefaultOptions(b: *Build) !BuildOptions {
 }
 
 pub fn addExecutable(b: *Build, comptime name: []const u8, options: ExecutableOptions) *Step {
+    // 1. Compilation and installation of the generated binary
     const exe = elf_compilation(b, name, &options);
     const exe_install = b.addInstallArtifact(exe, .{});
 
-    const flatten_output_file = name ++ ".flt";
+    // 2. Run objcopy on the compiler output (generated from above step) and install the output into
+    // the 'bin' folder.
     const objcopy_run = b.addSystemCommand(&.{ "objcopy", "-O", "binary" });
+    objcopy_run.step.dependOn(&exe_install.step);
+
+    const flatten_output_file = name ++ ".flt";
     objcopy_run.addArg(b.getInstallPath(.bin, exe.name));
     const flatten_output_path = objcopy_run.addOutputFileArg(flatten_output_file);
 
     const flatten_install = b.addInstallFileWithDir(flatten_output_path, .bin, flatten_output_file);
 
-    objcopy_run.step.dependOn(&exe_install.step);
-    return &flatten_install.step;
+    // 3. A Root target for the above steps. This was added so that 'zig build <name>' can be used
+    // to build one particular target.
+    const root = b.step(name, "Builds '" ++ name ++ "' target.");
+    root.dependOn(&flatten_install.step);
+    return root;
 }
 
 fn elf_compilation(b: *Build, comptime name: []const u8, options: *const ExecutableOptions) *Step.Compile {