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+# TreePKG
+
+`treepkg` is a tool for recursively building packages from an ABS tree. It has
+been tested while building packages for the mips64el port and it has proven to
+be useful.
+
+It was written having in mind the experience of `fullpkg`, which converted to
+`fullpkg-ng` and then splitted into `fullpkg-build` and `fullpkg-find`. It's
+aim is to simplify algorithms implemented on the fullpkg family, while solving
+some design issues that made fullpkg miss some packages sometimes.
+
+
+## Requirements
+
+`treepkg` needs the help of `toru-path` for "indexing" an ABS tree. `toru-path`
+stores a tokyocabinet database of "pkgname" => "path" pairs, where pkgname is
+replaced by the "pkgbase", "pkgname", and "provides" fields of a PKGBUILD,
+followed by the path of the current PKGBUILD.
+
+This information is then used by `treepkg` to know where to find the PKGBUILD
+of a package. The fullpkg family needed to guess this by traversing the full
+ABS tree, and therefore it was unable to find pkgnames that differ from
+pkgbase.
+
+So, to use `treepkg` you need to run `toru-path` after the ABS tree update.
+
+> Split PKGBUILDs make it difficult to extract metadata if it's stored inside
+> package() functions. This will happen with the provides field and `treepkg`
+> won't find that linux-libre-headers provides linux-headers, for instance.
+
+## How does it work
+
+`treepkg` must be run from the path of the PKGBUILD you're going to build (this
+may change over time). This will be DEPTH=0 and it will create a temporary
+directory to work on in the format /tmp/pkgbase-treepkg-random-string. Inside
+this directory, it will copy the needed PKGBUILDs prefixed with their depth
+number. The first package will always be copied to 000\_pkgbase.
+
+From then on, treepkg sources the PKGBUILD and runs itself over all pkgnames on
+the depends and makedepends array, only if it detects their versions aren't
+already built or deprecated by newer ones, using the `is_built` utility.
+
+While processing this info, it will increase the depth of the packages. It'll
+also write a CSV file with the knowledge it acquires from the ABS tree (useful
+for debugging). This file is called BUILDORDER.
+
+When this process ends (no more needed dependencies are found), the temporary
+work dir is traversed in inverse order (from higher depths to 0) running the
+FULLBUILDCMD from libretools.conf and then the HOOKLOCALRELEASE variable, which
+*must* provide a way to `repo-add` the packages to an available repository, so
+the next build will find and install the newer version using pacman.
+
+For instance, having this as the first pacman repository (on /etc/pacman.conf):
+
+    [stage3]
+    Server = /var/cache/pacman/pkg
+
+And this on /etc/makepkg.conf:
+
+    PKGDEST=/var/cache/pacman/pkg
+
+Your HOOKLOCALRELEASE script should look like this:
+
+    # Get needed vars
+    source /etc/makepkg.conf
+    source /etc/libretools.conf
+    source PKGBUILD
+
+    unset build package check
+    
+    fullver=$(full_version ${epoch:-0} ${pkgver} ${pkgrel})
+    pkgs=()
+    
+    # Generate canonical package paths
+    msg "Adding packages to [stage3]..."
+    for name in ${pkgname[@]}; do
+        msg2 "${name} ${fullver}"
+        pkgs+=("${PKGDEST}/${name}-${fullver}-*.pkg.tar.*")
+    done
+    
+    # Add the packages to a local 
+    repo-add ${PKGDEST}/stage3.db.tar.gz ${pkgs[@]}
+
+    # Stage the packages for later releasing
+    librestage $1
+
+> Note the first HOOKLOCALRELEASE argument is the remote repository name (core,
+> extra, etc.)
+
+There's a special case when a dependency depends on another that was put on
+a depth level lower than itself. In this case the build order will be wrongly
+assumed and you may end up with broken packages.
+
+To explain it with an example:
+
+    ghostscript (0) - fontconfig (1)
+                    \ cups (1)       - fontconfig (ignored)
+
+The second time fontconfig appears, it will be ignored. In this case cups will
+build against an fontconfig version that will be outdated by the fontconfig
+version at depth 1. In this cases, `treepkg` will detect it cached the
+dependency on a lower depth, and will "bury" it to a depth higher than the
+current one. Thus this will become the build path:
+
+    ghostscript (0) - fontconfig (buried)
+                    \ cups (1)            - fontconfig (2)
+
+> Note: currently, `treepkg` doesn't perform recursive burying, so if you hit
+> a really long build tree with some circular dependencies you may find
+> packages buried several times and queued to build before their actuals deps.
+
+## Tips 
+
+`treepkg` accepts two arguments: 1) the temporary work dir and 2) the next
+depth level it should use (if current equals 0, it'll pass 1). You don't need
+to pass this arguments when running it manually, they're used internally to
+automatically construct the build path.
+
+But if a build failed, `treepkg` will cancel itself immediately informing you
+where the leftovers files were left. If you pass this path to `treepkg` as the
+first argument, it will resume the build, skipping to the last package being
+packaged.
+
+You can take the opportunity given by this to modify the build path or the
+PKGBUILDs, without having to run `treepkg` twice. For instance you can remove
+a package from the build order, or move it manually, or update the PKGBUILD
+that made `treepkg` fail in the first place. You can force a skipped package
+(after building it manually) by using `touch built_ok` on the PKGBUILD dir.
+
+You don't probably want to mess with the second argument though.