Incorrect circular reference error

Question

Our team had been using Delphi 6 for many years, then switched to Delphi 2006 years ago. With both versions we have the following problem: frequently the compiler complains about a unit which is supposedly used recursively. This unit is a 40k LOC unit which is at the core of a project with almost 1 million LOC (third party included).

The error message is incorrect: a full build on the project always works. Unfortunately, the error message does not tell us where the supposed circular reference is, just the name of that unit. Sometimes it even happens that valid error messages are listed 2-4 times until that circular reference problem is "found". Clearly the compiler is running in a circle here. Because of the size of that project it is hard to find the problem manually. Therefore I made a tool which proves that there really is no circular reference (the tool creates a directed dependency graph of the units and determines the coherence components in that graph - there are none except if I deliberately put some in).

This is not only affecting F9 compilation but also code completion / insight which is not working most of the time. Sometimes it works when I press ctrl-space a second time...

Any ideas how we can isolate or even fix the problem? Note that it will be very hard to split the 40k LOC unit into smaller ones because it contains about 15 large classes which depend on each other in the interface section (I know it's bad but should work anyway).

Update
We are constantly refactoring but this is one tough unit to refactor because everything depends on everything, almost. Have been trying to get around it via interfaces but we are talking about some classes with 100s of methods and properties. And it would be slower.

Upgrading to D2009 may be an option down the road but right now we're stuck with D2006 (the unicode stuff and the price tag are two of the stoppers here). Question is anyway if it would help since the problem is in there since D6 at least.

About trimming the uses clauses, we have been doing this frequently with Icarus. But that did not help so far. We are down to 90 custom units in the interface section now. However, with a true circular reference the problem could be in any unit. Also tried to add all units to the dpr.

The project shares a lot of code with other projects, and there are some IFDEFs. However, the defines are not set up in project options but via a common include file. Therefore all modules should see the same defines. Also, the problem reoccurs shortly after a full rebuild without switching to another project.

Answer 1

I will probably be downvoted for this. In D2005 I had a 10k loc unit (datamodule) that flat out stopped compiling. Had to separate out some datasets/code to another datamodule. That 10k unit was and is a mess. You really should consider refactoring out some code to other units. My module has since D2005 / separation grown even worse, but it still compiles in D2007. So my answer is a) refactor and b) upgrade to D2009.

Answer 2

It seems clear that this is due to a slight difference between the background compiler and the real thing. You could look around (QualityCentral) what's known on that topic.

Also, since you didn't explicitly state this, you should remove unnecessary units and move uses statements down to implementation if possible. Maybe your tool could help with this.

And just to be sure you should check the unit aliases and Path settings.