ci: don't error in check-guide on main (#5936)

Author: davidhewitt

noxfile.py

@@ -769,39 +769,45 @@ def check_guide(session: nox.Session):
 
     exclude_args = [f"--exclude={arg}" for arg in excludes]
 
-    # check all links in the guide
-    _run(
-        session,
-        "lychee",
-        "--include-fragments",
-        str(PYO3_GUIDE_TARGET),
-        *remap_args,
-        *exclude_args,
-        "--accept=200,429",
-        "--cache",
-        "--max-cache-age=7d",
-        f"--root-dir={PYO3_GUIDE_TARGET}",
-        *session.posargs,
-        external=True,
-    )
-    # check external links in the docs
-    # (intra-doc links are checked by rustdoc)
-    _run(
-        session,
-        "lychee",
-        str(PYO3_DOCS_TARGET),
-        *remap_args,
-        f"--exclude=file://{PYO3_DOCS_TARGET}",
-        # exclude some old http links from copyright notices, known to fail
-        *exclude_args,
-        "--accept=200,429",
-        # reduce the concurrency to avoid rate-limit from `pyo3.rs`
-        "--max-concurrency=32",
-        "--cache",
-        "--max-cache-age=7d",
-        *session.posargs,
-        external=True,
-    )
+    try:
+        # check all links in the guide
+        _run(
+            session,
+            "lychee",
+            "--include-fragments",
+            str(PYO3_GUIDE_TARGET),
+            *remap_args,
+            *exclude_args,
+            "--accept=200,429",
+            "--cache",
+            "--max-cache-age=7d",
+            f"--root-dir={PYO3_GUIDE_TARGET}",
+            *session.posargs,
+            external=True,
+        )
+        # check external links in the docs
+        # (intra-doc links are checked by rustdoc)
+        _run(
+            session,
+            "lychee",
+            str(PYO3_DOCS_TARGET),
+            *remap_args,
+            f"--exclude=file://{PYO3_DOCS_TARGET}",
+            # exclude some old http links from copyright notices, known to fail
+            *exclude_args,
+            "--accept=200,429",
+            # reduce the concurrency to avoid rate-limit from `pyo3.rs`
+            "--max-concurrency=32",
+            "--cache",
+            "--max-cache-age=7d",
+            *session.posargs,
+            external=True,
+        )
+    except nox.command.CommandFailed:
+        # on `main`, we ignore link check failures to allow the site to still be updated on push to main,
+        # we want to run the link checker on main to populate the GitHub actions cache so PRs run more reliably.
+        if os.environ.get("GITHUB_REF", "") != "refs/heads/main":
+            raise
 
 
 @nox.session(name="format-guide", venv_backend="none")