Improve dynamic require of requires analysis

Skip tests under some conditions, with explicit message.

Issue error, if any, on the command thread so message is reflected up
to Emacs for users to see.

racket/commands/requires.rkt

@@ -55,42 +55,43 @@
         "(require net/url\n         (combine-in net/url\n                     racket/format))")
        (replace 39 42 "(require net/uri-codec\n         net/url)")))
 
-    ;; On older Rackets macro-debugger/analysis/check-requires might
-    ;; give error:
-    ;;
-    ;; derivation-parser: error on token #2: <local-value,
-    ;;#<syntax:/usr/share/racket/collects/syntax/parse/private/lib.rkt:63:55
-    ;;-string>>
-    (when (version<=? "8.14" (version))
-      (check-equal?
-       (requires/trim p)
-       '((delete 174 17)
-         (replace
-          129
-          44
-          "(require net/url\n         (combine-in net/url\n                     racket/format))")
-         (replace 39 42 "(require net/uri-codec\n         net/url)")))
-      (check-equal?
-       (requires/base p)
-       '((delete 174 17)
-         (replace
-          129
-          44
-          "(require (for-syntax racket/base)\n         net/url\n         (combine-in net/url\n                     racket/format)\n         racket/list\n         racket/match)")
-         (replace 39 42 "(require net/uri-codec\n         net/url)"))))))
+    (cond
+      [(not show-requires)
+       (displayln "Skipping requires analysis tests (macro-debugger-text-lib seemingly not installed).")]
+      ;; On older Rackets macro-debugger/analysis/check-requires might
+      ;; give error:
+      ;;   derivation-parser: error on token #2: <local-value, #<syntax:/usr/share/racket/collects/syntax/parse/private/lib.rkt:63:55 -string>>
+      [(version<? (version) "8.14")
+       (displayln "Skipping requires analysis tests (Racket < 8.14).")]
+      [else
+       (check-equal?
+        (requires/trim p)
+        '((delete 174 17)
+          (replace
+           129
+           44
+           "(require net/url\n         (combine-in net/url\n                     racket/format))")
+          (replace 39 42 "(require net/uri-codec\n         net/url)")))
+       (check-equal?
+        (requires/base p)
+        '((delete 174 17)
+          (replace
+           129
+           44
+           "(require (for-syntax racket/base)\n         net/url\n         (combine-in net/url\n                     racket/format)\n         racket/list\n         racket/match)")
+          (replace 39 42 "(require net/uri-codec\n         net/url)")))])))
 
 ;;; analysis by macro-debugger/analysis/check-requires
 
-(define (error-thunk)
-  (error 'requires
-         "Cannot work until you `raco pkg install macro-debugger-lib`"))
-
 (define show-requires
   (safe-dynamic-require 'macro-debugger/analysis/check-requires
                         'show-requires
-                        error-thunk))
+                        (λ () #f)))
 
 (define (analyze path-str)
+  (unless show-requires
+    (error 'analyze-requires
+           "Cannot work until you `raco pkg install macro-debugger-text-lib`"))
   (define-values (base name _) (split-path (string->path path-str)))
   (parameterize ([current-load-relative-directory base]
                  [current-directory base])