From: Nutchanon Wetchasit Date: Tue, 05 May 2020 12:03:38 GMT Subject: `git am` always fails applying patch from `git format-patch -U0` Message-ID: <20200505190338.1155dcfd@WINDOW-NB> Hello folks, I was rewriting a committed change in my repository via a workflow of git-format-patch -> edit -> git-am. The edit I wanted to make was just a one-line change in the diff, with no line number shift, so I generated patches with no context line (`git format-patch -U0`) to avoid subsequent patch failure caused by context change. But the problem was that `git-am` appeared to erroneously reject such patches for an unclear reason... After editing patches, hard-resetting the branch to the parent commit of the chain; I fed the patches to `git am`, and encountered an error that looked like this: > Applying: Removing second line > error: patch failed: text.txt:2 > error: text.txt: patch does not apply > Patch failed at 0001 Removing second line > hint: Use 'git am --show-current-patch=diff' to see the failed patch > When you have resolved this problem, run "git am --continue". > If you prefer to skip this patch, run "git am --skip" instead. > To restore the original branch and stop patching, run "git am --abort". The first thing I thought, was that I somehow messed up my patches somewhere in the edit. So I canceled the patching process with `git am --abort`, hard-reset the branch again, and re-attempted running `git am` with *unmodified* patches series; and found that `git am` still produced the same error, which ruled out the factor of my editing mistakes. (Why would Git refuse a patch generated by itself?) To be sure, I retried this on a dummy repository, with only one non-modified zero-context patch; and the error was still consistently reproducible. I'm not sure what caused Git to reject such zero-context patches; although some hints could be seen when running `git apply --verbose` with the offending patch file. (See step 9 in "Exact steps to reproduce" below) GNU Patch would happily apply the same patch without any error though. Nevertheless, this does not happen when the patch was generated with 1 or more context lines. So the workaround would be using `git format-patch -U1` instead, with more risk of rejects on context change caused by editing. ----- General steps to reproduce follows: 1. Make any disposable Git repository with two or more commits on `master` branch. 2. Generate a zero-context patch of the latest commit with `git format-patch -U0 HEAD^` 3. Remove the latest commit with `git reset --hard HEAD^` 4. Re-add the commit via the patch from step 2, with `git-am`; it would claim that the patch does not apply. Compare and contrast: try the same, but change step 2 to `git format-patch -U1` HEAD^`, and you would see that `git-am` accept it normally. ----- Exact steps to reproduce follows: 1. Create an empty Git repository, with dummy user name and email: $ mkdir am-nocontext $ cd am-nocontext $ git init $ git config user.name "Joe Average" $ git config user.email "joe@example.com" 2. Create a dummy 3-line text file, add it as the first commit: $ printf "One\nTwo\nThree\n" > text.txt $ git add text.txt $ git commit -m "Initial commit" 3. Remove the second line from that file, make it a second commit: $ printf "2d\nwq\n" | ed text.txt $ git commit -am "Removing second line" 4. Generate patch from the second commit, with *zero* context line: $ git format-patch -U0 HEAD^ 5. Back out the second commit: $ git reset --hard HEAD^ 6. Add back the second commit using the patch from step 4: $ git am 0001-Removing-second-line.patch Applying: Removing second line error: patch failed: text.txt:2 error: text.txt: patch does not apply Patch failed at 0001 Removing second line hint: Use 'git am --show-current-patch=diff' to see the failed patch When you have resolved this problem, run "git am --continue". If you prefer to skip this patch, run "git am --skip" instead. To restore the original branch and stop patching, run "git am --abort". ^ You would find that Git reported that patching was failed, when it should not be. 8. Cancel the patching process: $ git am --abort 9. Try re-applying the same patch to the working tree using Git: $ git apply --verbose 0001-Removing-second-line.patch Checking patch text.txt... error: while searching for: Two error: patch failed: text.txt:2 error: text.txt: patch does not apply ^ You would see that somehow Git tried to take the first line in the hunk as a context, even when it wasn't marked as such. 10. Apply the same patch using GNU diffutils' `patch` program: $ patch -p 1 -i 0001-Removing-second-line.patch patching file text.txt $ git diff diff --git a/text.txt b/text.txt index 4fcefbf..3146b8f 100644 --- a/text.txt +++ b/text.txt @@ -1,3 +1,2 @@ One -Two Three ^ You would find that GNU Patch would apply the same patch correctly. The full terminal transcript is attached as , which also includes intermediate informational steps, and also displays the exact patch content produced by the process. ----- System information follows... Git: 2.26.2 (source) Patch: GNU diffutils 2.6.1 (Debian) System: Debian GNU/Linux 7.0 Wheezy i386 Locale: th_TH (local encoding TIS-620) Note that this problem appears to exist for long way down to at least Git 1.7.10.4 (the original version I found this error), if not earlier. Please advice in case I overlooked something. Regards, Nutchanon Wetchasit $ cd /tmp $ mkdir am-nocontext $ cd am-nocontext $ git init Initialized empty Git repository in /tmp/am-nocontext/.git/ $ git config user.name "Joe Average" $ git config user.email "joe@example.com" $ printf "One\nTwo\nThree\n" > text.txt $ cat text.txt One Two Three $ git add text.txt $ git commit -m "Initial commit" [master (root-commit) e2e0c16] Initial commit 1 file changed, 3 insertions(+) create mode 100644 text.txt $ git log --pretty=oneline e2e0c16f6d31bc8e673494ecc92d1e8f377275aa (HEAD -> master) Initial commit $ printf "2d\nwq\n" | ed text.txt 14 10 $ cat text.txt One Three $ git diff diff --git a/text.txt b/text.txt index 4fcefbf..3146b8f 100644 --- a/text.txt +++ b/text.txt @@ -1,3 +1,2 @@ One -Two Three $ git commit -am "Removing second line" [master 27e6e8b] Removing second line 1 file changed, 1 deletion(-) $ git log --pretty=oneline 27e6e8bdc3ecbecc17f5ec1407f97f1977054461 (HEAD -> master) Removing second line e2e0c16f6d31bc8e673494ecc92d1e8f377275aa Initial commit $ git format-patch -U0 HEAD^ 0001-Removing-second-line.patch $ cat 0001-Removing-second-line.patch From 27e6e8bdc3ecbecc17f5ec1407f97f1977054461 Mon Sep 17 00:00:00 2001 From: Joe Average Date: Tue, 5 May 2020 18:17:52 +0700 Subject: [PATCH] Removing second line --- text.txt | 1 - 1 file changed, 1 deletion(-) diff --git a/text.txt b/text.txt index 4fcefbf..3146b8f 100644 --- a/text.txt +++ b/text.txt @@ -2 +1,0 @@ One -Two -- 2.26.2 $ git reset --hard HEAD^ HEAD is now at e2e0c16 Initial commit $ git log --pretty=oneline e2e0c16f6d31bc8e673494ecc92d1e8f377275aa (HEAD -> master) Initial commit $ git am 0001-Removing-second-line.patch Applying: Removing second line error: patch failed: text.txt:2 error: text.txt: patch does not apply Patch failed at 0001 Removing second line hint: Use 'git am --show-current-patch=diff' to see the failed patch When you have resolved this problem, run "git am --continue". If you prefer to skip this patch, run "git am --skip" instead. To restore the original branch and stop patching, run "git am --abort". $ git am --abort $ git diff $ git log --pretty=oneline e2e0c16f6d31bc8e673494ecc92d1e8f377275aa (HEAD -> master) Initial commit $ git apply --verbose 0001-Removing-second-line.patch Checking patch text.txt... error: while searching for: Two error: patch failed: text.txt:2 error: text.txt: patch does not apply $ git log --pretty=oneline e2e0c16f6d31bc8e673494ecc92d1e8f377275aa (HEAD -> master) Initial commit $ git diff $ patch -p 1 -i 0001-Removing-second-line.patch patching file text.txt $ git diff diff --git a/text.txt b/text.txt index 4fcefbf..3146b8f 100644 --- a/text.txt +++ b/text.txt @@ -1,3 +1,2 @@ One -Two Three $ exit