[pkg/stanza] Fix issue where checkpoints could be lost during abrupt shutdown (#29610)

Fixes #29609
Fixes #29491

Author: djaglowski

.chloggen/pkg-stanza-sync-current-files.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: Fix problem where checkpoints could be lost when collector is shutdown abruptly
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: filelogreceiver
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [29609, 29491]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

pkg/stanza/fileconsumer/file.go

@@ -150,7 +150,12 @@ func (m *Manager) poll(ctx context.Context) {
 	// Any new files that appear should be consumed entirely
 	m.readerFactory.FromBeginning = true
 	if m.persister != nil {
-		if err := checkpoint.Save(context.Background(), m.persister, m.knownFiles); err != nil {
+		allCheckpoints := make([]*reader.Metadata, 0, len(m.knownFiles)+len(m.previousPollFiles))
+		allCheckpoints = append(allCheckpoints, m.knownFiles...)
+		for _, r := range m.previousPollFiles {
+			allCheckpoints = append(allCheckpoints, r.Metadata)
+		}
+		if err := checkpoint.Save(context.Background(), m.persister, allCheckpoints); err != nil {
 			m.Errorw("save offsets", zap.Error(err))
 		}
 	}