Improve compression format detection

by checking if a version is already on the pristine-tar branch and use
it's compression type if found.

LP: #615212

gbp/git.py

@@ -259,6 +259,18 @@ def show(self, id):
         for line in commit:
             yield line
 
+    def grep_log(self, regex, where=None):
+        args = ['--pretty=format:%H']
+        args.append("--grep=%s" % regex)
+        if where:
+            args.append(where)
+        args.append('--')
+
+        commits, ret = self.__git_getoutput('log', args)
+        if ret:
+            raise GitRepositoryError, "Error grepping log for %s" % regex
+        return [ commit.strip() for commit in commits[::-1] ]
+
     def get_subject(self, commit):
         """Gets the subject of a commit"""
         self.__check_path()

git-buildpackage

@@ -175,7 +175,7 @@ def extract_orig(orig_tarball, dest_dir):
         os.rmdir(tar_topdir)
 
 
-def guess_comp_type(repo, comp_type):
+def guess_comp_type(repo, comp_type, srcpkg, upstream_version):
     """Guess compression type"""
 
     if comp_type != 'auto':
@@ -188,7 +188,13 @@ def guess_comp_type(repo, comp_type):
         if not repo.has_branch(PristineTar.branch):
             comp_type = 'gzip'
         else:
-            tarball = repo.get_subject(PristineTar.branch)
+            regex = 'pristine-tar .* %s_%s\.orig.tar\.' % (srcpkg, upstream_version)
+            commits = repo.grep_log(regex, PristineTar.branch)
+            if commits:
+                commit = commits[0]
+            else:
+                commit = PristineTar.branch
+            tarball = repo.get_subject(commit)
             comp_type = du.get_compression(tarball)
             if not comp_type:
                 comp_type = 'gzip'
@@ -341,9 +347,9 @@ def main(argv):
             else:
                 tarball_dir = output_dir
 
-            options.comp_type = guess_comp_type (repo, options.comp_type)
             # Get/build the orig.tar.gz if necessary:
             if not du.is_native(cp):
+                options.comp_type = guess_comp_type(repo, options.comp_type, cp['Source'], major)
                 orig_file = du.orig_file(cp, options.comp_type)
 
                 # look in tarball_dir first, if found force a symlink to it