fix: stg import --reject should create empty commit

When trying to import a patch that does not apply cleanly, and using
--reject option, stg should apply what it can, leave the rest in .rej
files, and create an empty commit. The work to apply the patch is
outsourced to "git apply --reject" which exits with status code 1 if
patch is applied partially and it is treated as error by stg import.

Fix the issue by treating exit codes less than 128 from "git apply
--reject" as success (128 signals hard error).

Also add a test case and fix up documentation for "stg import".

Closes: #471

Signed-off-by: Dmitry Torokhov <dtor@google.com>

src/cmd/import.rs

@@ -44,8 +44,10 @@ fn make() -> clap::Command {
              allows the patches source to be fetched from a url instead of from a \
              local file.\n\
              \n\
-             If a patch does not apply cleanly, the failed diff is written to a \
-             .stgit-failed.patch file and an empty patch is added to the stack.\n\
+             If a patch does not apply cleanly import is aborted unless '--reject' \
+             is specified, in which case it will apply to the work tree the parts \
+             of the patch that are  applicable, leave the rejected hunks in \
+             corresponding *.rej files, and add an empty patch to the stack.\n\
              \n\
              The patch description must be separated from the diff with a \"---\" line.",
         )

src/stupid/context.rs

@@ -148,10 +148,18 @@ impl<'repo, 'index> StupidContext<'repo, 'index> {
         if let Some(context_lines) = context_lines {
             command.arg(format!("-C{context_lines}"));
         }
+        let error_threshold = if reject {
+            // When allowing rejects "git apply" returns exit code 1 when it can't
+            // apply patch in its entirety. Exit code 128 is a hard error.
+            128
+        } else {
+            // Any non-zero error code is considered an error.
+            1
+        };
         command
             .stdout(Stdio::null())
             .in_and_out(diff)?
-            .require_success("apply --index")?;
+            .require_code_less_than("apply --index", error_threshold)?;
         Ok(())
     }
 

t/t1800-import.sh

@@ -366,6 +366,16 @@ test_expect_success 'Import series from stdin' '
     stg delete --top
 '
 
+test_expect_success 'Import patch that does not apply cleanly with --reject' '
+    stg import --reject "$TEST_DIRECTORY"/t1800/diff-with-rejects &&
+    git log -1 --pretty=format:%b >body &&
+    test_when_finished "rm foo.txt.rej body" &&
+    test "$(echo $(stg top))" = "diff-with-rejects" &&
+    test_line_count = 0 body &&
+    stg reset --hard &&
+    stg delete --top
+'
+
 test_expect_success STG_IMPORT_URL 'Attempt url' '
     general_error stg import --url 2>err &&
     grep -e "required arguments were not provided" err

t/t1800/diff-with-rejects

@@ -0,0 +1,29 @@
+test patch with rejects
+
+---
+
+ t/t1800/foo.txt | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/t/t1800/foo.txt b/t/t1800/foo.txt
+index ad01662f..d609de80 100644
+--- a/foo.txt
++++ b/foo.txt
+@@ -6,7 +6,7 @@ dobidim
+ dobidum
+ dobodam
+ dobodim
+-dobodum
++dObodum
+ dibedam
+ dibedim
+ dibedum
+@@ -18,7 +18,7 @@ dibodim
+ dibodum
+ dabedam
+ dabedim
+-Dabedum
++dAbedum
+ dabidam
+ dabidim
+ dabidum