[Bug 2743] New: - More sophisticated dependency analysis

[bu...@apache.org]

http://nagoya.apache.org/bugzilla/show_bug.cgi?id=2743

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+ +============================================================================+
+ | More sophisticated dependency analysis                                     |
+ +----------------------------------------------------------------------------+
+ |        Bug #: 2743                        Product: Ant                     |
+ |       Status: NEW                         Version: unspecified             |
+ |   Resolution:                            Platform: Other                   |
+ |     Severity: Enhancement              OS/Version: All                     |
+ |     Priority: Other                     Component: Core                    |
+ +----------------------------------------------------------------------------+
+ |  Assigned To: ant-dev@jakarta.apache.org                                   |
+ |  Reported By: Jochen.Schwarze@cit.de                                       |
+ |      CC list: Cc:                                                          |
+ +----------------------------------------------------------------------------+
+ |          URL:                                                              |
+ +============================================================================+
+ |                              DESCRIPTION                                   |
+ To the Ant team:
+ 
+ When I read the documents for the Ant2 re-design, I remembered a Perl-based 
+ make system named "cons", now at <http://www.dsmit.com/cons/>. Like Ant, cons 
+ tries to be a better make. There are two design decisions or features that make 
+ cons unique:
+ 
+ 1) Cons never calls itself recursively, so it can process the whole dependency 
+ tree in one pass. Actually, cons parses a hierarchy of declarative "Construct" 
+ files and analyses the entire hierarchy before it starts building. This is MUCH 
+ better than the usual make approach with make processes calling themselves 
+ recursively, breaking the dependency chain every time.
+ 
+ 2) Cons keeps hash keys (MD5 message digests, actually) of all dependencies and 
+ targets it has seen and processed (including external influences like the 
+ system environment and compiler flags), so it can detect very reliably if 
+ anything has changed and needs a rebuild.
+ 
+ Example #1: If you touch a source's modification date, that source will not be 
+ considered as changed as long as the file contents don't change; if you change 
+ a target, that target will be rebuilt if it doesn't fit to the current set of 
+ dependencies.
+ 
+ Example #2: You compile a subtree or a project with debugging enabled. When you 
+ re-build the entire project (say, with optimization enabled), cons will re-
+ compile exactly these files that previously have not been compiled with 
+ optimization enabled, because it records the set of command-line options used 
+ for building each target.
+ 
+ I have used cons for years in C/C++ building, and I haven't yet come across a 
+ build system that is nearly as reliable.
+ 
+ As it is, cons is not very well suited for Java applications. Cons follows a 
+ strict dependency hierarchy, where a set of sources always leads to ONE result. 
+ (Java dependency analysis is more difficult, and the class files that are 
+ created during compilation are -- seen from the outside -- essentially random.)
+ 
+ Anyway, it might be inspiring to look at cons' design from the perspective of 
+ specifying Ant2.
+ 
+ Best,
+ 
+   Jochen