Add tails of logs of failed packages to github comments

Snippets will be hidden under dropdown sections so as not to clutter UI.
Snippets are limited to 20 lines, and if too many logs are generated,
the report is truncated so that it fits into a single github comment.

Signed-off-by: Ihar Hrachyshka <[email protected]>

Author: booxter

nixpkgs_review/report.py

@@ -12,11 +12,18 @@
 from .nix import Attr
 from .utils import System, info, link, skipped, system_order_key, to_link, warn
 
+# https://github.com/orgs/community/discussions/27190
+MAX_GITHUB_COMMENT_LENGTH = 65536
+
 
 def get_log_filename(a: Attr, system: str) -> str:
     return f"{a.name}-{system}.log"
 
 
+def get_log_dir(root: Path) -> Path:
+    return root / "logs"
+
+
 def print_number(
     logs_dir: Path,
     system: str,
@@ -59,6 +66,28 @@ def html_pkgs_section(
     return res
 
 
+def get_file_tail(file: Path, lines: int = 20) -> str:
+    try:
+        with file.open("rb") as f:
+            f.seek(0, os.SEEK_END)
+            end = f.tell()
+            f.seek(max(end - lines * 1024, 0), os.SEEK_SET)
+            return "\n".join(
+                f.read().decode("utf-8", errors="replace").splitlines()[-lines:]
+            )
+    except OSError:
+        return ""
+
+
+def html_failed_section(logs_dir: Path, packages: list[Attr], system: str) -> str:
+    res = "<details>\n"
+    for pkg in packages:
+        tail = get_file_tail(logs_dir / get_log_filename(pkg, system))
+        res += f"  <summary>{pkg.name}</summary>\n<pre>{tail}</pre>\n"
+    res += "</details>\n"
+    return res
+
+
 class LazyDirectory:
     def __init__(self, path: Path) -> None:
         self.path = path
@@ -112,7 +141,7 @@ def write_error_logs(
     *,
     max_workers: int | None = 1,
 ) -> None:
-    logs = LazyDirectory(directory.joinpath("logs"))
+    logs = LazyDirectory(get_log_dir(directory))
     results = LazyDirectory(directory.joinpath("results"))
     failed_results = LazyDirectory(directory.joinpath("failed_results"))
 
@@ -272,10 +301,10 @@ def built_packages(self) -> dict[System, list[str]]:
         }
 
     def write(self, directory: Path, pr: int | None) -> None:
-        directory.joinpath("report.md").write_text(self.markdown(pr))
-        directory.joinpath("report.json").write_text(self.json(pr))
-
+        # write logs first because snippets from them may be needed for the report
         write_error_logs(self.attrs, directory, max_workers=self.max_workers)
+        directory.joinpath("report.md").write_text(self.markdown(directory, pr))
+        directory.joinpath("report.json").write_text(self.json(pr))
 
     def succeeded(self) -> bool:
         """Whether the report is considered a success or a failure"""
@@ -301,7 +330,7 @@ def json(self, pr: int | None) -> str:
             indent=4,
         )
 
-    def markdown(self, pr: int | None) -> str:
+    def markdown(self, root: Path, pr: int | None) -> str:
         msg = ""
         if self.show_header:
             msg += "## `nixpkgs-review` result\n\n"
@@ -346,6 +375,18 @@ def markdown(self, pr: int | None) -> str:
             )
             msg += html_pkgs_section(":white_check_mark:", report.built, "built")
 
+        for system, report in self.system_reports.items():
+            if not report.failed:
+                continue
+            full_msg = msg
+            full_msg += "\n---\n"
+            full_msg += f"### Error logs: `{system}`\n"
+            full_msg += html_failed_section(get_log_dir(root), report.failed, system)
+            # if the final message won't fit a single github comment, stop
+            if len(full_msg) > MAX_GITHUB_COMMENT_LENGTH:
+                break
+            msg = full_msg
+
         return msg
 
     def print_console(self, root: Path, pr: int | None) -> None:
@@ -354,7 +395,7 @@ def print_console(self, root: Path, pr: int | None) -> None:
             info("\nLink to currently reviewing PR:")
             link(to_link(pr_url, pr_url))
 
-        logs_dir = root / "logs"
+        logs_dir = get_log_dir(root)
         for system, report in self.system_reports.items():
             info(f"--------- Report for '{system}' ---------")
             p = functools.partial(print_number, logs_dir, system)