Fix usage of pg_waldump --ignore option (#7578)

Previously, the --ignore option was only used when reading from a single
file.
With this PR pg_waldump -i is enough to open any neon WAL segments

test_runner/regress/test_pg_waldump.py

@@ -0,0 +1,46 @@
+import os
+
+from fixtures.neon_fixtures import NeonEnv, PgBin
+from fixtures.utils import subprocess_capture
+
+
+# Simple test to check that pg_waldump works with neon WAL files
+def test_pg_waldump(neon_simple_env: NeonEnv, test_output_dir, pg_bin: PgBin):
+    env = neon_simple_env
+    env.neon_cli.create_branch("test_pg_waldump", "empty")
+    endpoint = env.endpoints.create_start("test_pg_waldump")
+
+    cur = endpoint.connect().cursor()
+    cur.execute(
+        """
+        BEGIN;
+        CREATE TABLE t1(i int primary key, n_updated int);
+        INSERT INTO t1 select g, 0 from generate_series(1, 50) g;
+        ROLLBACK;
+    """
+    )
+
+    cur.execute(
+        """
+        BEGIN;
+        CREATE TABLE t1(i int primary key, n_updated int);
+        INSERT INTO t1 select g, 0 from generate_series(1, 50) g;
+        COMMIT;
+    """
+    )
+
+    # stop the endpoint to make sure that WAL files are flushed and won't change
+    endpoint.stop()
+
+    assert endpoint.pgdata_dir
+    wal_path = os.path.join(endpoint.pgdata_dir, "pg_wal/000000010000000000000001")
+    pg_waldump_path = os.path.join(pg_bin.pg_bin_path, "pg_waldump")
+
+    # use special --ignore option to ignore the validation checks in pg_waldump
+    # this is necessary, because neon WAL files contain gap at the beginning
+    output_path, _, _ = subprocess_capture(test_output_dir, [pg_waldump_path, "--ignore", wal_path])
+
+    with open(f"{output_path}.stdout", "r") as f:
+        stdout = f.read()
+        assert "ABORT" in stdout
+        assert "COMMIT" in stdout