Adding a duplicate header filename in mozbuild caused an error to manifest downstream while building: 1) detect duplicate list elements early in mozbuild. These may not be easy to spot when variables are assigned on different lines or by conditionals. xpcom/glue/moz.build EXPORT += [ 'nsCycleCollectionTraversalCallback.h', 'nsCycleCollectorUtils.h', <<---** 'nsCycleCollectorUtils.h', <<---** 'nsDataHashtable.h', A try job failed, only on win7, with the following error: http://tbpl.mozilla.org/php/getParsedLog.php?id=24529425&tree=Try make.py[6]: Entering directory 'e:\builds\moz2_slave\try-w32-0000000000000000000000\build\obj-firefox\xpcom\glue' Target '../../dist/include/nsCycleCollectorUtils.h' has multiple rules with commands. <export>: Found error tbpl: the view brief log link is only able to report the problem as 'Summary is empty' 2) tbpl may be able to parse or at least match /Found error/. The header file is derived found from the line above in xpcom/glue. The error message reported was generic '<export>: Found error'. Mentioning the source file or working directory as part of the <export> error message would make it easier to locate the source rather than matching up source lines from the log. That might also give tbpl more context for reporting a clear error.

(In reply to jarmstrong from comment #0) > tbpl: the view brief log link is only able to report the problem as 'Summary > is empty' > 2) tbpl may be able to parse or at least match /Found error/. Agree there are a number of build failures that no longer match TBPL's regex - I'll fix this in bug 482177.

Shall we morph this bug into making the error string clearer, and then leave the necessary TBPL regexp tweaks to bug 482177 ? If that's ok with you, once this bug is resolved, I'll add whatever regexp is necessary in the other bug :-)

By clearer, I mean the suggestions in the last paragraph of comment 0 :-)