Fix ?(#TAB method search name exploration (#52555)

Fix #52551.

This PR ensures that a `SomeModule.?(...#TAB` completion can only
suggests method `foo` such that `SomeModule.foo` exists (by checking
`isdefined(SomeModule, :foo)`). This is equivalent, I believe, to the
initial implementation of #38791,
less the bug.

Now that we have #51345, we may want to relax the above condition
somewhat to include public names present in modules loaded into
`SomeModule`, so that, for instance, a direct completion of `?(` would
include `@assume_effects`. This could be good for method exploration
because even though typing `@assume_effects` with no qualification in
`Main` will error, the error now includes the helpful message
```
Hint: a global variable of this name also exists in Base.
```
But that can wait for a later PR anyway, this one is just the bugfix.

The bug mentioned at
#52551 (comment)
dates from the initial #38791 so this could be backported as far back as
v1.8.

---------

Co-authored-by: Shuhei Kadowaki <[email protected]>
(cherry picked from commit a987f56)

stdlib/REPL/src/REPLCompletions.jl

@@ -7,7 +7,7 @@ export completions, shell_completions, bslash_completions, completion_text
 using Core: CodeInfo, MethodInstance, CodeInstance, Const
 const CC = Core.Compiler
 using Base.Meta
-using Base: propertynames, something
+using Base: propertynames, something, IdSet
 
 abstract type Completion end
 
@@ -659,6 +659,26 @@ function complete_methods(ex_org::Expr, context_module::Module=Main, shift::Bool
 end
 
 MAX_ANY_METHOD_COMPLETIONS::Int = 10
+function recursive_explore_names!(seen::IdSet, callee_module::Module, initial_module::Module, exploredmodules::IdSet{Module}=IdSet{Module}())
+    push!(exploredmodules, callee_module)
+    for name in names(callee_module; all=true, imported=true)
+        if !Base.isdeprecated(callee_module, name) && !startswith(string(name), '#') && isdefined(initial_module, name)
+            func = getfield(callee_module, name)
+            if !isa(func, Module)
+                funct = Core.Typeof(func)
+                push!(seen, funct)
+            elseif isa(func, Module) && func ∉ exploredmodules
+                recursive_explore_names!(seen, func, initial_module, exploredmodules)
+            end
+        end
+    end
+end
+function recursive_explore_names(callee_module::Module, initial_module::Module)
+    seen = IdSet{Any}()
+    recursive_explore_names!(seen, callee_module, initial_module)
+    seen
+end
+
 function complete_any_methods(ex_org::Expr, callee_module::Module, context_module::Module, moreargs::Bool, shift::Bool)
     out = Completion[]
     args_ex, kwargs_ex, kwargs_flag = try
@@ -674,32 +694,8 @@ function complete_any_methods(ex_org::Expr, callee_module::Module, context_modul
     # semicolon for the ".?(" syntax
     moreargs && push!(args_ex, Vararg{Any})
 
-    seen = Base.IdSet()
-    for name in names(callee_module; all=true)
-        if !Base.isdeprecated(callee_module, name) && isdefined(callee_module, name) && !startswith(string(name), '#')
-            func = getfield(callee_module, name)
-            if !isa(func, Module)
-                funct = Core.Typeof(func)
-                if !in(funct, seen)
-                    push!(seen, funct)
-                    complete_methods!(out, funct, args_ex, kwargs_ex, MAX_ANY_METHOD_COMPLETIONS, false)
-                end
-            elseif callee_module === Main && isa(func, Module)
-                callee_module2 = func
-                for name in names(callee_module2)
-                    if !Base.isdeprecated(callee_module2, name) && isdefined(callee_module2, name) && !startswith(string(name), '#')
-                        func = getfield(callee_module, name)
-                        if !isa(func, Module)
-                            funct = Core.Typeof(func)
-                            if !in(funct, seen)
-                                push!(seen, funct)
-                                complete_methods!(out, funct, args_ex, kwargs_ex, MAX_ANY_METHOD_COMPLETIONS, false)
-                            end
-                        end
-                    end
-                end
-            end
-        end
+    for seen_name in recursive_explore_names(callee_module, callee_module)
+        complete_methods!(out, seen_name, args_ex, kwargs_ex, MAX_ANY_METHOD_COMPLETIONS, false)
     end
 
     if !shift

stdlib/REPL/test/replcompletions.jl

@@ -140,6 +140,10 @@ let ex = quote
         struct WeirdNames end
         Base.propertynames(::WeirdNames) = (Symbol("oh no!"), Symbol("oh yes!"))
 
+        # https://github.com/JuliaLang/julia/issues/52551#issuecomment-1858543413
+        export exported_symbol
+        exported_symbol(::WeirdNames) = nothing
+
         end # module CompletionFoo
         test_repl_comp_dict = CompletionFoo.test_dict
         test_repl_comp_customdict = CompletionFoo.test_customdict
@@ -740,6 +744,9 @@ end
 
 #TODO: @test_nocompletion("CompletionFoo.?(3; len2=5; ")
 
+# https://github.com/JuliaLang/julia/issues/52551
+@test !isempty(test_complete("?("))
+
 #################################################################
 
 # Test method completion with varargs