Undo the decision to publish incomplete types to the binding table

base/boot.jl

@@ -985,6 +985,14 @@ Unsigned(x::Union{Float16, Float32, Float64, Bool}) = UInt(x)
 Integer(x::Integer) = x
 Integer(x::Union{Float16, Float32, Float64}) = Int(x)
 
+# During definition of struct type `B`, if an `A.B` expression refers to
+# the eventual global name of the struct, then return the partially-initialized
+# type object.
+# TODO: remove. This is a shim for backwards compatibility.
+function struct_name_shim(@nospecialize(x), name::Symbol, mod::Module, @nospecialize(t))
+    return x === mod ? t : getfield(x, name)
+end
+
 # Binding for the julia parser, called as
 #
 #    Core._parse(text, filename, lineno, offset, options)

src/julia-syntax.scm

@@ -963,6 +963,19 @@
         (ctors-min-initialized (car expr))
         (ctors-min-initialized (cdr expr)))))
 
+(define (insert-struct-shim field-types name)
+  (map (lambda (x)
+      (expr-replace (lambda (y)
+                      (and (length= y 3) (eq? (car y) '|.|)
+                            (or (equal? (caddr y) `(quote ,name))
+                                (equal? (caddr y) `(inert ,name)))))
+                    x
+                    (lambda (y)
+                      `(call (core struct_name_shim)
+                              ,(cadr y) ,(caddr y)
+                              (thismodule) ,name))))
+        field-types))
+
 (define (struct-def-expr- name params bounds super fields0 mut)
   (receive
    (fields defs) (separate eventually-decl? fields0)
@@ -1022,11 +1035,9 @@
                                                               prev
                                                               params)
                                                       (quote parameters))))
-                               '()))
-                  ;; otherwise do an assignment to trigger an error
-                  (const (globalref (thismodule) ,name) ,name)))
-             (const (globalref (thismodule) ,name) ,name))
-         (call (core _typebody!) ,name (call (core svec) ,@field-types))
+                               '())))))
+         (call (core _typebody!) ,name (call (core svec) ,@(insert-struct-shim field-types name)))
+         (const (globalref (thismodule) ,name) ,name)
          (null)))
        ;; "inner" constructors
        (scope-block

src/utils.scm

@@ -48,6 +48,13 @@
                 (any (lambda (y) (expr-contains-p p y filt))
                      (cdr expr))))))
 
+(define (expr-replace p expr repl)
+  (cond ((p expr) (repl expr))
+        ((and (pair? expr) (not (quoted? expr)))
+         (cons (car expr)
+               (map (lambda (x) (expr-replace p x repl)) (cdr expr))))
+        (else expr)))
+
 ;; find all subexprs satisfying `p`, applying `key` to each one
 (define (expr-find-all p expr key (filt (lambda (x) #t)))
   (if (filt expr)

test/core.jl

@@ -7669,7 +7669,7 @@ end
 end
 @test fieldtypes(M36104.T36104) == (Vector{M36104.T36104},)
 @test_throws ErrorException("expected") @eval(struct X36104; x::error("expected"); end)
-@test @isdefined(X36104)
+@test !@isdefined(X36104)
 struct X36104; x::Int; end
 @test fieldtypes(X36104) == (Int,)
 primitive type P36104 8 end