Add first-parent option (True by default)

bisect/bisect.py

@@ -6,7 +6,7 @@
 import subprocess
 
 
-def bisect(good, bad, e3sm_path, load_script, config_file):
+def bisect(good, bad, e3sm_path, load_script, config_file, first_parent):
     """
     The driver function for calling ``git bisect`` to find the first "bad"
     commit between a known "good" and "bad" commit.
@@ -31,8 +31,12 @@ def bisect(good, bad, e3sm_path, load_script, config_file):
         build the MPAS component to test.
     config_file : str
         The relative or absolute path to a config file containing config
-        options similar to ``bisect/exanmple.cfg`` that control the bisection
+        options similar to ``bisect/example.cfg`` that control the bisection
         process.
+    first_parent : bool
+        Whether to only follow the first parent for merge commits.  This is
+        typically desirable because there may be broken commits within a branch
+         that are fixed by the time the branch is merged.
     """
 
     e3sm_path = os.path.abspath(e3sm_path)
@@ -41,9 +45,14 @@ def bisect(good, bad, e3sm_path, load_script, config_file):
 
     cwd = os.getcwd()
 
+    if first_parent:
+        flags = '--first-parent'
+    else:
+        flags = ''
+
     commands = f'source {load_script}; ' \
                f'cd {e3sm_path}; ' \
-               f'git bisect start; ' \
+               f'git bisect start {flags}; ' \
                f'git bisect good {good}; ' \
                f'git bisect bad {bad}; ' \
                f'git bisect run {cwd}/bisect/bisect_step.py' \
@@ -74,7 +83,8 @@ def main():
     bisect(good=section['good'], bad=section['bad'],
            e3sm_path=section['e3sm_path'],
            load_script=section['load_script'],
-           config_file=args.config_file)
+           config_file=args.config_file,
+           first_parent=section.getboolean('first_parent'))
 
 
 if __name__ == '__main__':

bisect/example.cfg

@@ -6,6 +6,10 @@
 good = 44814ae
 # The hash or tag of a bad commit where the tests fail
 bad = 7b87d1f
+# whether to only follow the first parent for merge commits.  This is typically
+# desirable because there may be broken commits within a branch that are fixed
+# by the time the branch is merged.
+first_parent = True
 # the absolute or relative path to the base of the E3SM branch you want to build
 e3sm_path = E3SM-Project
 # the absolute or relative path to the MPAS model directory you want to build