Normalize PG18 error messages and window references in test outputs

src/test/regress/bin/normalize.sed

@@ -395,3 +395,14 @@ s/\<is referenced from table\>/is still referenced from table/g
 s/^[[:space:]]*ERROR:[[:space:]]+subscription "[^"]+" could not connect to the publisher:[[:space:]]*/ERROR:  could not connect to the publisher: /I
 # PG18: drop verbose 'connection to server … failed:' preamble
 s/^[[:space:]]*ERROR:[[:space:]]+could not connect to the publisher:[[:space:]]*connection to server .* failed:[[:space:]]*/ERROR:  could not connect to the publisher: /I
+
+# PG18: replace named window refs like "OVER w1" with neutral "OVER (?)"
+# this rule can be removed when PG18 is the minimum supported version
+# only on Sort Key / Group Key / Output lines
+# Sort Key
+/^[[:space:]]*Sort Key:/ s/(OVER[[:space:]]+)w[0-9]+/\1(?)/g
+# Group Key
+/^[[:space:]]*Group Key:/ s/(OVER[[:space:]]+)w[0-9]+/\1(?)/g
+# Output
+/^[[:space:]]*Output:/   s/(OVER[[:space:]]+)w[0-9]+/\1(?)/g
+# end PG18 window ref normalization

src/test/regress/expected/multi_test_helpers.out

@@ -736,6 +736,9 @@ begin
         IF ln ~ '^[[:space:]]*Index[[:space:]]+Searches:[[:space:]]*[0-9]+[[:space:]]*$' THEN
           CONTINUE;
         END IF;
+        IF ln ~ '^[[:space:]]*Window:[[:space:]].*$' THEN  -- e.g., "Window: w1 AS (...)"
+            CONTINUE;
+        END IF;
 
         -- Replace any numeric word with just 'N'
         ln := regexp_replace(ln, '-?\m\d+\M', 'N', 'g');

src/test/regress/sql/multi_test_helpers.sql

@@ -767,6 +767,9 @@ begin
         IF ln ~ '^[[:space:]]*Index[[:space:]]+Searches:[[:space:]]*[0-9]+[[:space:]]*$' THEN
           CONTINUE;
         END IF;
+        IF ln ~ '^[[:space:]]*Window:[[:space:]].*$' THEN  -- e.g., "Window: w1 AS (...)"
+            CONTINUE;
+        END IF;
 
         -- Replace any numeric word with just 'N'
         ln := regexp_replace(ln, '-?\m\d+\M', 'N', 'g');