string-search robustness and documentation improvement (bug#43598)

* src/fns.c (Fstring_search): Check START-POS argument range.
Simplify logic.  Improve doc string.
* test/src/fns-tests.el (string-search): Add test cases.
* doc/lispref/strings.texi (Text Comparison): Elaborate.
* lisp/emacs-lisp/byte-opt.el (pure-fns): Mark string-search as pure.

1 files changed, 29 insertions, 1 deletions

diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index 8c2b1300dce..323743d8420 100644
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -907,6 +907,12 @@
   (should (equal (string-search "foo" "foobarzot") 0))
   (should (not (string-search "fooz" "foobarzot")))
   (should (not (string-search "zot" "foobarzo")))
+  (should (equal (string-search "ab" "ab") 0))
+  (should (equal (string-search "ab\0" "ab") nil))
+  (should (equal (string-search "ab" "abababab" 3) 4))
+  (should (equal (string-search "ab" "ababac" 3) nil))
+  (let ((case-fold-search t))
+    (should (equal (string-search "ab" "AB") nil)))
 
   (should (equal
            (string-search (make-string 2 130)
@@ -923,4 +929,26 @@
   (should (not (string-search (make-string 1 255) "a\377ø")))
   (should (not (string-search (make-string 1 255) "a\377a")))
 
-  (should (equal (string-search "fóo" "zotfóo") 3)))
+  (should (equal (string-search "fóo" "zotfóo") 3))
+
+  (should (equal (string-search (string-to-multibyte "\377") "ab\377c") 2))
+  (should (equal (string-search "\303" "aøb") nil))
+  (should (equal (string-search "\270" "aøb") nil))
+  ;; This test currently fails, but it shouldn't!
+  ;;(should (equal (string-search "ø" "\303\270") nil))
+
+  (should-error (string-search "a" "abc" -1))
+  (should-error (string-search "a" "abc" 4))
+  (should-error (string-search "a" "abc" 100000000000))
+
+  (should (equal (string-search "a" "aaa" 3) nil))
+  (should (equal (string-search "\0" "") nil))
+
+  (should (equal (string-search "" "") 0))
+  (should-error (string-search "" "" 1))
+  (should (equal (string-search "" "abc") 0))
+  (should (equal (string-search "" "abc" 2) 2))
+  (should (equal (string-search "" "abc" 3) 3))
+  (should-error (string-search "" "abc" 4))
+  (should-error (string-search "" "abc" -1))
+  )