Build Flags

You can customize build and linker flags applied to your C, C++, and assembly source files in Megaton.toml, using the build.flags object.

There are 5 properties that can be set:

• common: Common flags for all processes
• c : Flags for compiling C sources .c
• cxx : Flags for compiling C++ sources .cpp, .cc, .cxx, .c++
• as: Flags for compiling assembly sources .s, .asm
• ld: Flags for linking

Each flag property is an array of strings:

[build.flags]
common = ["<default>"] 
c = ["<default>", "-DDEBUG"] 
cxx = ["<default>"]
as = ["<default>"]
ld = ["<default>"]

The string <default> is a special token used to include the default flags that are maintained by the megaton build tool plus extending from another set of flags (for example, the default flags of cxx include all c flags).

The default flags can be found here, and the flag extension behavior is detailed below.

Each property is also optional. If it's not set, it's equivalent to ["<default>"]. Setting a property to an empty array [] means not add any flags.

Includes and Libraries

Includes and libraries should be specified in build.includes, build.libpaths, and build.libraries respectively. See here for more details.

The build tool will also automatically include the headers for libmegaton and link with your project's rust code if the [rust] top-level section is configured.

Profiles

The build flags also support the profile system.

The profile-specific flags for a profile foo is defined at build.profiles.foo.flags. The flags are merged with flags from the base build.flags in the following way:

• If a property is not specified, it will be the same as the ones in build.flags
• If a property is specified, it will be appended to the ones in build.flags

For example:

[build.flags]
c = ["<default>", "-DDEBUG"]

[build.profiles.foo.flags]
c = ["-DFOO=1"]

The C flags for the base profile will be the default flags plus -DDEBUG, while the C flags for the foo profile will be the default flags plus -DDEBUG -DFOO=1.

There isn't a way to remove flags from the base profile. Typically, when you find yourself needing to remove a flag, you can restructure the flags and configure profile defaults to get the desired behavior for selecting profile with command line.

For example, if you want to build with -DDEBUG by default, and change it to -DNODEBUG for the release profile, you can do:

[profile]
default = "debug"
allow-base = false

[build.flags]

[build.profiles.debug.flags]
c = ["<default>", "-DDEBUG"]

[build.profiles.release.flags]
c = ["<default>", "-DNODEBUG"]

With this configuration megaton build will build with -DDEBUG and megaton build -p release will build with -DNODEBUG.