Mirah Office Hours

This time I tried to tackle the improperly generated main bug that’s been a problem with java source generation for a while. It took me a couple of hours to figure out where the relevant code was because I’m not as familiar with that part of the compiler.

The problem was that when the main method was generated for a file with the same name as a class in it, the source for the class’s source code would be generated before the main method’s body.

huh? Lets see some examples

Say we have a file test.mirah that looks like this:

When we run mirahc -j test.mirah, we get this Test.java out:

Notice anything funny? The main method isn’t finished. This is because when we generate the main method, we compile the whole script–which includes the class. The problem is that we finish generating the class’s source code before we get to Test.new.a, leaving the main we added to the class unfinished.

My hackish solution to this was to check if we were generating a main or not in the class source builder, and not finish the class until the main method was finished. I did this by checking to see if we were in a main method generation in the class generator and not finishing the class source generation until after the main method was generated if that’s true. But of course, that by itself added new problems because you can have multiple classes in a .mirah file. So I added a klass method on the Mirah::JavaSource::MethodBuilder so I could check both whether we are in a main method and whether it is the main method of the current class.

After doing that, the generated code looks like this:

Much better

Since I haven’t written tests specifically for this yet, I put it on a branch on my fork of Mirah so I can get some other eyeballs on it. I’m also sure there’s a better approach than the one I took.

One other thing I found is that if the name of the .mirah file is different than any of the classes in it, it compiles correctly even w/o the patch. Which makes sense because in that case there is no class body for the class with the same name as the file.

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