> On 9 Apr 2019, at 03:58, Mike Franklin via dmd-internals
> <[email protected]> wrote:
>
> That's an awfully broad question. I'm no expert in DMD, but I do dabble in
> the source code often.
>
> I'd start here: https://wiki.dlang.org/DMD_Source_Guide The information
> there is old but still relevant.
>
> This is my mental model and understanding
>
> source code --> lexer.d --> tokesn
> tokens --> parse.d --> expressions (see expression.d)
> expressions --> expressionsem.d --> lowered expressions
> lowered expressions --> e2ir --> intermediate representation (I'm awufully
> vauge on this)
> After that it's in the backend, and that's pretty much a black box to me.
I can add to the above that the parser is a subclass of the lexer. The parser
will retrieve the next token when it needs to, to continue parsing. The parsing
is initiated from `Module.parse` in `dmodule.d` [1] which will then call
`Parser.parseModule` in `parse.d`. After that the semantic analyzing phase will
begin with the call to `dsymbolSemantic` for each module given to the compiler.
This is all available in `mars.d`, which contains the entry point of the
compiler.
> Tracing with `printf` is your friend, which is why you see so many commented
> `printf` statements in the source code. You should be able to print out
> almost anything with with the `toChars()` method (e.g. `printf("%s\n",
> whatever.toChars());`)
For debugging I can also recommend tracing with `std.stdio.writeln` and
`std.stdio.writefln`. Although it's not allowed to use Phobos in the compiler,
it’s perfectly fine to use it during development and debugging. Just make sure
that all traces of Phobos are gone when making a PR. Most classes will have a
`toString` method which is doing exactly the same thing as `toChars`, but it
will return a D string instead of a C string. `writeln` knows about this and
will call `toString` automatically. When printing an enum value with `writeln`,
it will print the name of the enum member instead of it’s value, I like that
very much. It’s also much easier to print D string with `writeln` than with
`printf`. This is especially useful when we’re trying to get rid of all C
strings and replace them with D strings.
[1]
https://github.com/dlang/dmd/blob/b4429221e0b0024e5f0b99e084e075f02972e19a/src/dmd/dmodule.d#L654
--
/Jacob Carlborg
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