expand and expand-to-top-form unset observer parameter

This change means that if a macro transformer calls expand (not
local-expand, but top-level expand), the macro debugger won't
receive the inner expand's events. Previously, the macro debugger
tried to parse and then discard the inner expand, but that was
brittle and complicated the grammar.

racket/src/expander/eval/main.rkt

@@ -57,7 +57,7 @@
     (per-top-level s ns 
                    #:single (lambda (s ns tail?)
                               (eval-compiled (compile s ns) ns tail?))
-                   #:observable? #f)]))
+                   #:observer #f)]))
 
 (define (eval-compiled c ns [as-tail? #t])
   (cond
@@ -88,7 +88,7 @@
                                                       serializable?
                                                       to-source?)))
                      #:combine append
-                     #:observable? #f)]))
+                     #:observer #f)]))
   (if (and (= 1 (length cs))
            (not (compiled-multiple-top? (car cs))))
       (car cs)
@@ -132,19 +132,21 @@
 ;; [Don't use keyword arguments here, because the function is
 ;;  exported for use by an embedding runtime system.]
 (define (expand s [ns (current-namespace)] [observable? #f] [to-parsed? #f] [serializable? #f])
-  (when observable? (log-expand-start-top))
-  (per-top-level s ns
-                 #:single (lambda (s ns as-tail?) (expand-single s ns observable? to-parsed? serializable?))
-                 #:combine cons
-                 #:wrap re-pair
-                 #:observable? observable?))
+  (define observer (and observable? (current-expand-observe)))
+  (when observer (...log-expand observer ['start-top]))
+  (parameterize ((current-expand-observe #f))
+    (per-top-level s ns
+                   #:single (lambda (s ns as-tail?) (expand-single s ns observer to-parsed? serializable?))
+                   #:combine cons
+                   #:wrap re-pair
+                   #:observer observer)))
 
-(define (expand-single s ns observable? to-parsed? serializable?)
+(define (expand-single s ns observer to-parsed? serializable?)
   (define rebuild-s (keep-properties-only s))
   (define ctx (make-expand-context ns
                                    #:to-parsed? to-parsed?
                                    #:for-serializable? serializable?
-                                   #:observable? observable?))
+                                   #:observer observer))
   (define-values (require-lifts lifts exp-s) (expand-capturing-lifts s ctx))
   (cond
    [(and (null? require-lifts) (null? lifts)) exp-s]
@@ -153,14 +155,14 @@
                                        lifts
                                        exp-s rebuild-s
                                        #:adjust-form (lambda (form)
-                                                       (expand-single form ns observable? to-parsed? serializable?)))]
+                                                       (expand-single form ns observer to-parsed? serializable?)))]
    [else
     (log-top-lift-begin-before ctx require-lifts lifts exp-s ns)
     (define new-s
       (wrap-lifts-as-begin (append require-lifts lifts)
                            #:adjust-form (lambda (form)
                                            (log-expand ctx 'next)
-                                           (expand-single form ns observable? to-parsed? serializable?))
+                                           (expand-single form ns observer to-parsed? serializable?))
                            #:adjust-body (lambda (form)
                                            (cond
                                              [to-parsed? form]
@@ -169,7 +171,7 @@
                                               ;; This re-expansion should be unnecessary, but we do it
                                               ;; for a kind of consistentcy with `expand/capture-lifts`
                                               ;; and for expansion observers
-                                              (expand-single form ns observable? to-parsed? serializable?)]))
+                                              (expand-single form ns observer to-parsed? serializable?)]))
                            exp-s
                            (namespace-phase ns)))
     (log-top-begin-after ctx new-s)
@@ -181,11 +183,11 @@
                  #:combine cons
                  #:wrap re-pair
                  #:just-once? #t
-                 #:observable? #t))
+                 #:observer #f))
 
 (define (expand-single-once s ns)
   (define-values (require-lifts lifts exp-s)
-    (expand-capturing-lifts s (struct*-copy expand-context (make-expand-context ns #:observable? #t)
+    (expand-capturing-lifts s (struct*-copy expand-context (make-expand-context ns)
                                             [just-once? #t])))
   (cond
    [(and (null? require-lifts) (null? lifts)) exp-s]
@@ -197,11 +199,13 @@
 (define (expand-to-top-form s [ns (current-namespace)])
   ;; Use `per-top-level` for immediate expansion and lift handling,
   ;; but `#:single #f` makes it return immediately
-  (log-expand-start-top)
-  (per-top-level s ns
-                 #:single #f
-                 #:quick-immediate? #f
-                 #:observable? #t))
+  (define observer (current-expand-observe))
+  (when observer (...log-expand observer ['start-top]))
+  (parameterize ((current-expand-observe #f))
+    (per-top-level s ns
+                   #:single #f
+                   #:quick-immediate? #f
+                   #:observer observer)))
 
 ;; ----------------------------------------
 
@@ -215,9 +219,9 @@
                        #:just-once? [just-once? #f] ; single expansion step
                        #:quick-immediate? [quick-immediate? #t]
                        #:serializable? [serializable? #f] ; for module+submodule expansion
-                       #:observable? observable?)
+                       #:observer observer)
   (define s (maybe-intro given-s ns))
-  (define ctx (make-expand-context ns #:observable? observable?))
+  (define ctx (make-expand-context ns #:observer observer))
   (define phase (namespace-phase ns))
   (let loop ([s s] [phase phase] [ns ns] [as-tail? #t])
     (define tl-ctx (struct*-copy expand-context ctx

racket/src/expander/expand/context.rkt

@@ -70,7 +70,7 @@
 (define (make-expand-context ns
                              #:to-parsed? [to-parsed? #f]
                              #:for-serializable? [for-serializable? #f]
-                             #:observable? [observable? #f])
+                             #:observer [observer #f])
   (define root-ctx (namespace-get-root-expand-ctx ns))
   (expand-context (root-expand-context-module-scopes root-ctx)
                   (root-expand-context-post-expansion-scope root-ctx)
@@ -107,7 +107,7 @@
                   #f   ; to-module-lifts
                   #f   ; requires+provides
                   #f   ; name
-                  (and observable? (current-expand-observe))
+                  observer
                   for-serializable?
                   #f))
 
@@ -136,8 +136,10 @@
 
 ;; ----------------------------------------
 
-;; For macro debugging; see "log.rkt"
-
+;; For macro debugging. This parameter is only used by the expander
+;; entry points in "../eval/main.rkt" to set the expand-context
+;; observer. Other expander code uses "log.rkt" to send expansion
+;; events to the observer.
 (define current-expand-observe (make-parameter #f
                                                (lambda (v)
                                                  (unless (or (not v)

racket/src/expander/expand/log.rkt

@@ -4,8 +4,7 @@
 (provide log-expand
          log-expand*
          log-expand...
-         ...log-expand
-         log-expand-start-top)
+         ...log-expand)
 
 (define-syntax log-expand...
   (syntax-rules (lambda)
@@ -45,11 +44,6 @@
             [(null? args) #f]
             [else (apply list* args)])))
 
-(define (log-expand-start-top)
-  (define obs (current-expand-observe))
-  (when obs
-    (call-expand-observe obs 'start-top)))
-
 (define key->arity
   ;; event-symbol => (U Nat 'any)
   #hash(;; basic empty tokens