# Building M2make

M2make is a front-end for the M2 Modula-2 compiler or GNU Modula-2 compiler.
It's goal is to check the order of compilation of the different files of a project, 
compiling only what is necessary. It only a main file like this :

```
M2make toto.mod
```

I will use a topological sort to figure out the order of compiling,
and which file needs to be compiled (if modified). 

I needs to compile only what is necessary.

## Status (implemented in `tools/m2make`, GNU Modula-2)

`M2make [-n] [-v] [-c m2|gm2] [-I dir] [-o out] [--m2bin path] [--shim path] main.mod`

- Follows `IMPORT`/`FROM` imports transitively from the main file,
  topologically sorts the modules (iterative DFS, cycle reported),
  skips the build when the output is newer than every source.
- `m2` mode: one session (`M2` + `qbe` + `cc`), gated on M2's
  `Parsed correctly` verdict. `gm2` mode: per-file `gm2 -fiso -c`
  of stale units + ordered link.
- One portable core (`M2make.mod` + `M2makeOS.def`, ISO Modula-2
  importing only `FileIO`/`M2makeOS`) compiles with both `gm2 -fiso`
  (`build_gm2.sh`) and the V3 `M2` driver (`build_m2.sh`); the
  OS layer (`stat`/`system`/text input) lives in `m2make_os.c`
  with per-compiler bindings (`M2makeC.def` for gm2,
  `EXTERNAL` for M2). See `tools/m2make/README.md` for the exact
  portable subset and limitations. `tests/run_tests.sh`: 18/18 green
  with both binaries.


I will use a topological sort to figure out the order of compiling,
and which file needs to be compiled (if modified). 

I needs to compile only what is necessary.


<!--It also needs eventually to use a project file with these elements :-->

<!--[compiler]-->
<!--	M2 or Gnu Modula-2-->
<!--	-->
<!--[systemlibs]-->
<!--	system libraries to be included-->
<!--	-->
<!--[projectfiles]-->
<!--	all the project files to be included in the project. -->
<!--	-->
<!--the last one can be deduced by M2make which will load the main file -->
<!--and follow all the imports to be included. From that, it makes a -->
<!--topologic sort and compiles what is necessary in the right order.-->

<!--[options]-->
<!--	options to use with the compilers and to pass to the compile line.-->