search: synonym / query expansion + 9 tests

A synonym map [(Term,[Term])] expands a query term to itself + synonyms
(expandTerm); synDocs unions and synRankTfIdf ranks the expanded set. 214/214.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/tests/syn.sx

@@ -0,0 +1,53 @@
+;; Extension — synonym / query expansion.
+;; synmap: car -> automobile, vehicle ; big -> large
+;; Corpus: 1 "fast car"  2 "shiny automobile"  3 "big truck"  4 "large house"  5 "vehicle review"
+
+(define
+  syn-setup
+  "synmap = [(\"car\", [\"automobile\", \"vehicle\"]), (\"big\", [\"large\"])]\nidx = indexDoc 5 \"vehicle review\" (indexDoc 4 \"large house\" (indexDoc 3 \"big truck\" (indexDoc 2 \"shiny automobile\" (indexDoc 1 \"fast car\" emptyIndex))))\n")
+
+(define
+  syn-cases
+  (list
+    (list
+      "expand term with synonyms"
+      "expandTerm synmap \"car\""
+      (list "car" "automobile" "vehicle"))
+    (list
+      "expand single synonym"
+      "expandTerm synmap \"big\""
+      (list "big" "large"))
+    (list "expand unknown term" "expandTerm synmap \"banana\"" (list "banana"))
+    (list
+      "syn docs union"
+      "synDocs synmap \"car\" idx"
+      (list 1 2 5))
+    (list
+      "syn docs single synonym"
+      "synDocs synmap \"big\" idx"
+      (list 3 4))
+    (list
+      "syn docs no synonyms"
+      "synDocs synmap \"house\" idx"
+      (list 4))
+    (list "syn docs absent" "synDocs synmap \"plane\" idx" (list))
+    (list
+      "syn rank expanded"
+      "synRankTfIdf synmap \"car\" idx"
+      (list 1 2 5))
+    (list
+      "syn rank single"
+      "synRankTfIdf synmap \"big\" idx"
+      (list 3 4))))
+
+(define
+  syn-results
+  (search-batch syn-setup (map (fn (c) (nth c 1)) syn-cases)))
+
+(map-indexed
+  (fn
+    (i c)
+    (hk-test (nth c 0) (nth syn-results i) (nth c 2)))
+  syn-cases)
+
+{:fail hk-test-fail :pass hk-test-pass :fails hk-test-fails}