fix: let failures to build from a single source fail fast (#640)

fixes #638

autosynth/synth.py

@@ -356,6 +356,7 @@ def synthesize_loop(
     """
     if not toolbox.versions:
         return 0  # No versions, nothing to synthesize.
+
     try:
         if multiple_prs:
             commit_count = 0
@@ -370,8 +371,31 @@ def synthesize_loop(
             return commit_count
     except Exception as e:
         logger.error(e)
-        pass  # Fall back to non-forked loop below.
+        # Fallback to the single_pr loop to try to make some progress.
+        synthesize_loop_single_pr(toolbox, change_pusher, synthesizer)
+        # But still report the failure.
+        raise
+
+    return synthesize_loop_single_pr(toolbox, change_pusher, synthesizer)
+
+
+def synthesize_loop_single_pr(
+    toolbox: SynthesizeLoopToolbox,
+    change_pusher: AbstractChangePusher,
+    synthesizer: AbstractSynthesizer,
+) -> int:
+    """Loops through all source versions and creates a commit for every version
+    changed that caused a change in the generated code.
 
+    This function creates a single pull request for all sources.
+    Arguments:
+        toolbox {SynthesizeLoopToolbox} -- a toolbox
+        change_pusher {AbstractChangePusher} -- Used to push changes to github.
+        synthesizer {AbstractSynthesizer} -- Invokes synthesize.
+
+    Returns:
+        int -- Number of commits committed to this repo.
+    """
     if change_pusher.check_if_pr_already_exists(toolbox.branch):
         return 0
     synthesize_inner_loop(toolbox, synthesizer)

tests/test_synth.py

@@ -446,17 +446,22 @@ def test_synthesize_loop_uses_single_commit_title_for_pr_title(
     assert golden_calls == calls
 
 
-def test_synthesize_loop_always_succeeds_when_latest_version_succeeds(
+def test_synthesize_loop_always_pushes_something_when_latest_version_succeeds(
     synthesize_loop_fixture: SynthesizeLoopFixture,
 ):
     histories = [
         [Failed(), WriteFile("a.txt", "a")],
         [Failed(), WriteFile("b.txt", "b")],
     ]
     source_versions = compile_histories(histories, synthesize_loop_fixture.synthesizer)
-    # Synthesize loop should not throw an exception.
-    commit_count = synthesize_loop_fixture.synthesize_loop(source_versions, True)
-    assert commit_count > 0
+    # Synthesize loop will throw an exception.
+    try:
+        synthesize_loop_fixture.synthesize_loop(source_versions, True)
+        assert False, "Expected an exception to be thrown."
+    except Exception:
+        pass
+    # But the loop still should have pushed a change.
+    synthesize_loop_fixture.change_pusher.push_changes.assert_called()
 
 
 def make_working_repo(working_dir: str):