Fail when git repository contains files supposed to be generated

boo#1230469

obs_scm_bridge

@@ -252,6 +252,9 @@ class ObsGit(object):
         line = self.run_cmd(cmd, cwd=outdir, fatal="git rev-parse")
         tstamp = line.rstrip()
         infofile = os.path.join(outdir, '_scmsync.obsinfo')
+        if os.path.exists(infofile):
+            logging.error("ERROR: The _scmsync.obsinfo file must not be part of the git repository.")
+            sys.exit(1)
         with open(infofile, "w") as obsinfo:
             obsinfo.write("mtime: " + tstamp + "\n")
             obsinfo.write("commit: " + commit + "\n")
@@ -382,6 +385,9 @@ class ObsGit(object):
     def write_info_file(self, filename: str, info: str) -> None:
         if not filename.startswith("/"):
             filename = self.outdir + "/" + filename
+        if os.path.exists(filename):
+            logging.error(f"ERROR: The {filename} file must not be part of the git repository.")
+            sys.exit(1)
         with open(filename, 'w') as infofile:
             infofile.write(info + '\n')
 
@@ -402,15 +408,23 @@ class ObsGit(object):
             return
         if projectscmsync:
             projecturlxml=f"""\n  <url>{escape(projectscmsync)}</url>"""
-        with open(f"{self.outdir}/{name}.xml", 'w') as xmlfile:
+        filename = f"{self.outdir}/{name}.xml"
+        if os.path.exists(filename):
+            logging.error(f"ERROR: The {name}.xml file must not be part of the git repository.")
+            sys.exit(1)
+        with open(filename, 'w') as xmlfile:
             xmlfile.write(f"""<package name="{escape(name)}">""")
             if self.enforce_bcntsynctag:
                 xmlfile.write(f"""<bcntsynctag>{escape(name)}</bcntsynctag>{projecturlxml}""")
             xmlfile.write(f"""<scmsync>{escape(url)}</scmsync>
 </package>\n""")
 
     def write_package_xml_local_link(self, target: str, name: str) -> None:
-        with open(f"{self.outdir}/{name}.xml", 'w') as xmlfile:
+        filename = f"{self.outdir}/{name}.xml"
+        if os.path.exists(filename):
+            logging.error(f"ERROR: The {name}.xml file must not be part of the git repository.")
+            sys.exit(1)
+        with open(filename, 'w') as xmlfile:
             xmlfile.write(f"""<package name="{escape(name)}">""")
             if self.enforce_bcntsynctag:
                 xmlfile.write(f"""<bcntsynctag>{escape(name)}</bcntsynctag>{projecturlxml}""")