git-p4: fix fast import when empty commit is first

From: Alisha Kim <[email protected]>

When executing p4 sync by specifying an excluded path, an empty commit will be created if there is only a change in the excluded path in revision.
If git-p4.keepEmptyCommits is turned off and an empty commit is the first, fast-import will fail.

---
git-p4: fix fast import when empty commit is first

When executing p4 sync by specifying an excluded path, an empty commit will be created if there is only a change in the excluded path in revision. If git-p4.keepEmptyCommits is turned off and an empty commit is the first, fast-import will fail.

The error log is as follows Ignoring revision 14035 as it would produce an empty commit. fast-import failed: warning: Not updating refs/heads/p4/master (new tip new commit hash does not contain parent commit hash) fast-import statistics: ...

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1609%2Fdaebo01%2Fgit-p4-pr-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1609/daebo01/git-p4-pr-v1
Pull-Request: https://github.com/git/git/pull/1609

 git-p4.py | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

index 0eb3bb4c47d..a61200e29e4 100755
@@ -3466,7 +3466,7 @@ class P4Sync(Command, P4UserMap):
         if not files and not allow_empty:
             print('Ignoring revision {0} as it would produce an empty commit.'
                 .format(details['change']))
-            return
+            return False
 
         self.gitStream.write("commit %s\n" % branch)
         self.gitStream.write("mark :%s\n" % details["change"])

@@ -3533,6 +3533,8 @@ class P4Sync(Command, P4UserMap):
                     print("Tag %s does not match with change %s: file count is different."
                            % (labelDetails["label"], change))
 
+        return True
+
     def getLabels(self):
         """Build a dictionary of changelists and labels, for "detect-labels"
            option.

@@ -3876,10 +3878,12 @@ class P4Sync(Command, P4UserMap):
                             self.commit(description, filesForCommit, branch, parent)
                 else:
                     files = self.extractFilesFromCommit(description)
-                    self.commit(description, files, self.branch,
+                    isCommitted = self.commit(description, files, self.branch,
                                 self.initialParent)
                     # only needed once, to connect to the previous commit
-                    self.initialParent = ""
+                    if isCommitted:
+                        self.initialParent = ""
+
             except IOError:
                 print(self.gitError.read())
                 sys.exit(1)

base-commit: cfb8a6e9a93adbe81efca66e6110c9b4d2e57169

gitgitgadget

The above describe under what condition a failure gets triggered, but there is no description on what approach the proposed solution takes. You could teach "fast-import" to deal with an empty commit properly, you could ignore empty commits and not produce input for the fast-import command, you could probably turn these initial empty commits into non-empty commits by adding dummy contents, etc. We want to see in our proposed log messages what solution was taken and how the solution was designed to satisfy what requirements. This is to help future developers who will have to change the code that is given by this patch, so that their updates can still adhere to what ever design criteria you had in working on this change [*].

Side note: Your solution might be to ignore empty commits despite keepEmptyCommits option is set (as I said, you did not describe it at all in the above, so this is a hypothetical example). If the reason behind choosing that design were "I just do not want it to fail---I do not care if the resulting history coming out of fast-import is crappy (I lose the p4 CL descriptions for these commits, even though the user wants to keep them)", then future developers can safely "fix" your fix here by turning the initial empty commits into non-empty ones by adding fake contents.

I've added explanations for the changes I suggested.

The problem with correct grammar that you mentioned has also been changed. Thank you for your good comments.

From: Alisha Kim <[email protected]>

When executing p4 sync by specifying an excluded path, an empty commit will be created if there is only a change in the excluded path in revision.
If git-p4.keepEmptyCommits is turned off and an empty commit is the first, fast-import will fail. Change the return type of the commit function from void to bool and return whether a commit has been created. This failure was prevented by modifying initialParent to be initialized only when a commit was actually created.

---
git-p4: fix fast import when empty commit is first

When executing p4 sync by specifying an excluded path, an empty commit will be created if there is only a change in the excluded path in revision. If git-p4.keepEmptyCommits is turned off and an empty commit is the first, fast-import will fail. Change the return type of the commit function from void to bool and return whether a commit has been created. This failure was prevented by modifying initialParent to be initialized only when a commit was actually created.

The error log is as follows Ignoring revision 14035 as it would produce an empty commit. fast-import failed: warning: Not updating refs/heads/p4/master (new tip new commit hash does not contain parent commit hash) fast-import statistics: ...

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1609%2Fdaebo01%2Fgit-p4-pr-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1609/daebo01/git-p4-pr-v2
Pull-Request: https://github.com/git/git/pull/1609

Range-diff vs v1:

1: f7c4fa18c4c ! 1: 1de9ac6dbf8 git-p4: fix fast import when empty commit is first
@@ Commit message
will be created if there is only a change in the excluded path in revision.
If git-p4.keepEmptyCommits is turned off and an empty commit is the
- first, fast-import will fail.
+ first, fast-import will fail. Change the return type of the commit
+ function from void to bool and return whether a commit has been
+ created. This failure was prevented by modifying initialParent
+ to be initialized only when a commit was actually created.

@@ git-p4.py: class P4Sync(Command, P4UserMap):
else:
files = self.extractFilesFromCommit(description)
- self.commit(description, files, self.branch,
-+ isCommitted = self.commit(description, files, self.branch,
++ haveCommitted = self.commit(description, files, self.branch,
self.initialParent)
# only needed once, to connect to the previous commit
- self.initialParent = ""
-+ if isCommitted:
++ if haveCommitted:
+ self.initialParent = ""
+
except IOError:

 git-p4.py | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

index 0eb3bb4c47d..1e3c0e815f0 100755
@@ -3466,7 +3466,7 @@ class P4Sync(Command, P4UserMap):
         if not files and not allow_empty:
             print('Ignoring revision {0} as it would produce an empty commit.'
                 .format(details['change']))
-            return
+            return False
 
         self.gitStream.write("commit %s\n" % branch)
         self.gitStream.write("mark :%s\n" % details["change"])

@@ -3533,6 +3533,8 @@ class P4Sync(Command, P4UserMap):
                     print("Tag %s does not match with change %s: file count is different."
                            % (labelDetails["label"], change))
 
+        return True
+
     def getLabels(self):
         """Build a dictionary of changelists and labels, for "detect-labels"
            option.

@@ -3876,10 +3878,12 @@ class P4Sync(Command, P4UserMap):
                             self.commit(description, filesForCommit, branch, parent)
                 else:
                     files = self.extractFilesFromCommit(description)
-                    self.commit(description, files, self.branch,
+                    haveCommitted = self.commit(description, files, self.branch,
                                 self.initialParent)
                     # only needed once, to connect to the previous commit
-                    self.initialParent = ""
+                    if haveCommitted:
+                        self.initialParent = ""
+
             except IOError:
                 print(self.gitError.read())
                 sys.exit(1)

base-commit: cfb8a6e9a93adbe81efca66e6110c9b4d2e57169

gitgitgadget