Re: Incremental Java Compile

Tom Anderson <>
Sun, 9 May 2010 16:26:12 +0100
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On Sun, 9 May 2010, Joshua Maurice wrote:

On May 9, 3:23?am, Tom Anderson <> wrote:

On Sat, 8 May 2010, Joshua Maurice wrote:

On May 7, 9:08?pm, "Mike Schilling" <>

Joshua Maurice wrote:

If anyone else cares, I managed to inadvertently stumble across a
solution. On impulse, I asked a co-worker at lunch. It seems that
class files do not contain sufficient information with default javac
options. However, when compiled with -g, it contains a listing of all
types used in the compile.

Are you sure?

$ javac -version
javac 1.6.0_16
$ echo "class Foo {public static final int X=23;}" >
$ echo "class Bar {public static final int Y=Foo.X;}" >
$ javac -g
$ grep Foo Bar.class

I can see no sign of Bar.class containing any mention of Foo.

Apparently I am mistaken. I would suggest looking for "Bar" and not
"Bar.class", but the result is the same. static finals might be an
exception to the debug information, which is sad. I'm wondering how
I'll work around this now.

I wonder how hard it would be to modify javac to add an attribute to
classes to record the origins of any inlined constants. That would let you
pull the information out from the class file later on, just as you can
already do with all the other types of dependency.

A bit of a poke around in the javac source code suggests it already has
code for tracking dependencies, which is there to support JWS in some way.
There are some flags that should switch it on (-xdepend, -Xdepend, -Xjws),
but they don't work on the version i have installled. There's also some
flag you can set on the compilation environment object that will make it
print dependencies, so if you're driving compilation from code, you should
be able to set that. You'd have to parse the compiler output, but that's
not that bad.

I am still in the process of implementing, so I haven't really been able
to test,

You're doing it wrong. Test first, test incrementally, build things in a
way you can test as you go. Before you start work for real, do a
higher-level test, a 'spike solution', to make sure that all your
assumptions (like this one) are valid.

Hopefully this is the only such corner case. I need more tests.

Always true!

Since you have this vast and terrifying codebase, you can probably
generate some pretty thorough functional tests from it. Take pairs of
adjacent revisions from source control, do full builds on each, find the
differences in output, then apply your tool and see if it comes up with
the right answers. You should be able to automate the process of turning a
pair of revisions into a test suite, and then you can just leave it to
crank away generating them for a few days.


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