reader: fix bugs in cdot readering

pkgs/racket-doc/scribblings/reference/reader.scrbl

@@ -956,16 +956,17 @@ When the @racket[read-cdot] @tech{parameter} is set to @racket[#t],
 then a variety of changes occur in the reader.
 
 First, symbols can no longer include the character @litchar{.}, unless
-the entire symbol is quoted with @litchar{|}.
+the @litchar{.} is quoted with @litchar{|} or @litchar{\}.
 
 Second, numbers can no longer include the character @litchar{.},
-unless the number is prefixed with @litchar{#e} or @litchar{#i}, or an
+unless the number is prefixed with @litchar{#e}, @litchar{#i},
+@litchar{#b}, @litchar{#o}, @litchar{#d}, @litchar{#x}, or an
 equivalent prefix as discussed in @secref["parse-number"]. If these
 numbers are followed by a @litchar{.} intended to be read as a C-style
-infix dot, then there must be separating whitespace.
+infix dot, then a delimiter must precede the @litchar{.}.
 
 Finally, after reading any datum @racket[_x], the reader will seek
-through whitespace and look for zero or more sequences of a
+through whitespace and comments and look for zero or more sequences of a
 @litchar{.} followed by another datum @racket[_y]. It will then group
 @racket[_x] and @racket[_y] together in a @racket[#%dot] form so that
 @racket[_x.y] reads equal to @racket[(#%dot _x _y)].

pkgs/racket-test-core/tests/racket/read.rktl

@@ -1356,7 +1356,19 @@
   (test '(#%dot (f a) (m b c))               readstr "(f a).(m b c)")
   (test '(#%dot (#%dot (f a) (m b c)) (n d e)) readstr "(f a).(m b c).(n d e)")
   (test '(#%dot (#%dot (#%dot (#%dot (#%dot (f a) (m b c)) x) (n d e)) y) z)
-        readstr "(f a).(m b c).x.(n d e).y.z"))
+        readstr "(f a).(m b c).x.(n d e).y.z")
+  (test '(#%dot 1.2 a) readstr "#i1.2 .a")
+  (test '(#%dot 1.0 a) readstr "#b1.0 .a")
+  (test '(#%dot 1.25 a) readstr "#o1.2 .a")
+  (test '(#%dot 1.2 a) readstr "#d1.2 .a")
+  (test '(#%dot 1.125 a) readstr "#x1.2 .a")
+  (test '(#%dot (#%dot 1 2) a) readstr "1.2 .a")
+  (test 'a.b readstr "|a.b|")
+  (test 'a.b readstr "a|.|b")
+  (test 'a.b readstr "a|.b|")
+  (test 'a.b readstr "a\\.b")
+  (err/rt-test (readstr "x.") exn:fail:read:eof?)
+  (err/rt-test (readstr "1.") exn:fail:read:eof?))
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; srcloc->string

racket/src/expander/read/main.rkt

@@ -153,8 +153,11 @@
          [(char=? ec #\.)
           (define-values (dot-line dot-col dot-pos) (port-next-location in))
           (consume-char in c)
-          (define cdot (wrap '#%dot in (reading-at config dot-line dot-col dot-pos) #\.))
+          (define pos-config (reading-at config dot-line dot-col dot-pos))
+          (define cdot (wrap '#%dot in pos-config #\.))
           (define post-v (read-undotted #f in config))
+          (when (eof-object? post-v)
+            (reader-error in pos-config #:due-to eof "expected a datum after cdot, found end-of-file"))
           (loop (wrap (list cdot v post-v) in (reading-at config line col pos) #\.))]
          [else v]))])]))
 

racket/src/expander/read/symbol-or-number.rkt

@@ -12,7 +12,7 @@
 
 (provide read-symbol-or-number)
 
-(define (read-symbol-or-number init-c in config
+(define (read-symbol-or-number init-c in orig-config
                                ;; `mode` can be 'symbol-or-number,
                                ;; 'symbol, 'symbol/indirect, 'keyword,
                                ;; or a number prefix string like "#e";
@@ -21,6 +21,9 @@
                                ;; symbol handler
                                #:mode [mode 'symbol-or-number]
                                #:extra-prefix [extra-prefix #f])
+  (define config (if (string? mode)
+                     (override-parameter read-cdot orig-config #f)
+                     orig-config))
   (define rt (read-config-readtable config))
   (cond
    [(and rt