fix #17997, don't load packages in Main

NEWS.md

@@ -205,6 +205,10 @@ This section lists changes that do not have deprecation warnings.
   * The `openspecfun` library is no longer built and shipped with Julia, as it is no longer
     used internally ([#22390]).
 
+  * All loaded packges used to have bindings in `Main` (e.g. `Main.Package`). This is no
+    longer the case; now bindings will only exist for packages brought into scope by
+    typing `using Package` or `import Package` ([#17997]).
+
   * `slicedim(b::BitVector, 1, x)` now consistently returns the same thing that `b[x]` would,
     consistent with its documentation. Previously it would return a `BitArray{0}` for scalar
     `x` ([#20233]).

base/interactiveutil.jl

@@ -566,7 +566,7 @@ end
 Return an array of methods with an argument of type `typ`.
 
 The optional second argument restricts the search to a particular module or function
-(the default is all modules, starting from Main).
+(the default is all top-level modules).
 
 If optional `showparents` is `true`, also return arguments with a parent type of `typ`,
 excluding type `Any`.
@@ -588,7 +588,7 @@ function methodswith(t::Type, f::Function, showparents::Bool=false, meths = Meth
     return meths
 end
 
-function methodswith(t::Type, m::Module, showparents::Bool=false)
+function _methodswith(t::Type, m::Module, showparents::Bool)
     meths = Method[]
     for nm in names(m)
         if isdefined(m, nm)
@@ -601,17 +601,12 @@ function methodswith(t::Type, m::Module, showparents::Bool=false)
     return unique(meths)
 end
 
+methodswith(t::Type, m::Module, showparents::Bool=false) = _methodswith(t, m, showparents)
+
 function methodswith(t::Type, showparents::Bool=false)
     meths = Method[]
-    mainmod = Main
-    # find modules in Main
-    for nm in names(mainmod)
-        if isdefined(mainmod, nm)
-            mod = getfield(mainmod, nm)
-            if isa(mod, Module)
-                append!(meths, methodswith(t, mod, showparents))
-            end
-        end
+    for mod in loaded_modules_array()
+        append!(meths, _methodswith(t, mod, showparents))
     end
     return unique(meths)
 end
@@ -678,8 +673,10 @@ download(url, filename)
     workspace()
 
 Replace the top-level module (`Main`) with a new one, providing a clean workspace. The
-previous `Main` module is made available as `LastMain`. A previously-loaded package can be
-accessed using a statement such as `using LastMain.Package`.
+previous `Main` module is made available as `LastMain`.
+
+If `Package` was previously loaded, `using Package` in the new `Main` will re-use the
+loaded copy. Run `reload("Package")` first to load a fresh copy.
 
 This function should only be used interactively.
 """

base/loading.jl

@@ -288,6 +288,7 @@ function reload(name::AbstractString)
         error("use `include` instead of `reload` to load source files")
     else
         # reload("Package") is ok
+        unreference_module(Symbol(name))
         require(Symbol(name))
     end
 end
@@ -315,21 +316,78 @@ all platforms, including those with case-insensitive filesystems like macOS and
 Windows.
 """
 function require(mod::Symbol)
-    _require(mod)
-    # After successfully loading, notify downstream consumers
-    if toplevel_load[] && myid() == 1 && nprocs() > 1
-        # broadcast top-level import/using from node 1 (only)
-        @sync for p in procs()
-            p == 1 && continue
-            @async remotecall_wait(p) do
-                if !isbindingresolved(Main, mod) || !isdefined(Main, mod)
-                    _require(mod)
+    if !root_module_exists(mod)
+        _require(mod)
+        # After successfully loading, notify downstream consumers
+        if toplevel_load[] && myid() == 1 && nprocs() > 1
+            # broadcast top-level import/using from node 1 (only)
+            @sync for p in procs()
+                p == 1 && continue
+                @async remotecall_wait(p) do
+                    require(mod)
+                    nothing
                 end
             end
         end
+        for callback in package_callbacks
+            invokelatest(callback, mod)
+        end
     end
-    for callback in package_callbacks
-        invokelatest(callback, mod)
+    return root_module(mod)
+end
+
+const loaded_modules = ObjectIdDict()
+const module_keys = ObjectIdDict()
+
+function register_root_module(key, m::Module)
+    if haskey(loaded_modules, key)
+        oldm = loaded_modules[key]
+        if oldm !== m
+            name = module_name(oldm)
+            warn("replacing module $name.")
+        end
+    end
+    loaded_modules[key] = m
+    module_keys[m] = key
+    nothing
+end
+
+register_root_module(:Core, Core)
+register_root_module(:Base, Base)
+register_root_module(:Main, Main)
+
+is_root_module(m::Module) = haskey(module_keys, m)
+
+root_module_key(m::Module) = module_keys[m]
+
+# This is used as the current module when loading top-level modules.
+# It has the special behavior that modules evaluated in it get added
+# to the loaded_modules table instead of getting bindings.
+baremodule __toplevel__
+using Base
+end
+
+# get a top-level Module from the given key
+# for now keys can only be Symbols, but that will change
+root_module(key::Symbol) = loaded_modules[key]
+
+root_module_exists(key::Symbol) = haskey(loaded_modules, key)
+
+loaded_modules_array() = collect(values(loaded_modules))
+
+function unreference_module(key)
+    if haskey(loaded_modules, key)
+        m = pop!(loaded_modules, key)
+        # need to ensure all modules are GC rooted; will still be referenced
+        # in module_keys
+    end
+end
+
+function register_all(a)
+    for m in a
+        if module_parent(m) === m
+            register_root_module(module_name(m), m)
+        end
     end
 end
 
@@ -364,7 +422,8 @@ function _require(mod::Symbol)
         if JLOptions().use_compiled_modules != 0
             doneprecompile = _require_search_from_serialized(mod, path)
             if !isa(doneprecompile, Bool)
-                return # success
+                register_all(doneprecompile)
+                return
             end
         end
 
@@ -391,14 +450,16 @@ function _require(mod::Symbol)
                 warn(m, prefix="WARNING: ")
                 # fall-through, TODO: disable __precompile__(true) error so that the normal include will succeed
             else
-                return # success
+                register_all(m)
+                return
             end
         end
 
         # just load the file normally via include
         # for unknown dependencies
         try
-            Base.include_relative(Main, path)
+            Base.include_relative(__toplevel__, path)
+            return
         catch ex
             if doneprecompile === true || JLOptions().use_compiled_modules == 0 || !precompilableerror(ex, true)
                 rethrow() # rethrow non-precompilable=true errors
@@ -411,6 +472,7 @@ function _require(mod::Symbol)
                 # TODO: disable __precompile__(true) error and do normal include instead of error
                 error("Module $mod declares __precompile__(true) but require failed to create a usable precompiled cache file.")
             end
+            register_all(m)
         end
     finally
         toplevel_load[] = last
@@ -532,7 +594,7 @@ function create_expr_cache(input::String, output::String, concrete_deps::Vector{
                       task_local_storage()[:SOURCE_PATH] = $(source)
                       end)
         end
-        serialize(in, :(Base.include(Main, $(abspath(input)))))
+        serialize(in, :(Base.include(Base.__toplevel__, $(abspath(input)))))
         if source !== nothing
             serialize(in, :(delete!(task_local_storage(), :SOURCE_PATH)))
         end
@@ -570,15 +632,9 @@ function compilecache(name::String)
     cachefile::String = abspath(cachepath, name*".ji")
     # build up the list of modules that we want the precompile process to preserve
     concrete_deps = copy(_concrete_dependencies)
-    for existing in names(Main)
-        if isdefined(Main, existing)
-            mod = getfield(Main, existing)
-            if isa(mod, Module) && !(mod === Main || mod === Core || mod === Base)
-                mod = mod::Module
-                if module_parent(mod) === Main && module_name(mod) === existing
-                    push!(concrete_deps, (existing, module_uuid(mod)))
-                end
-            end
+    for (key,mod) in loaded_modules
+        if !(mod === Main || mod === Core || mod === Base)
+            push!(concrete_deps, (key, module_uuid(mod)))
         end
     end
     # run the expression and cache the result
@@ -675,7 +731,7 @@ function stale_cachefile(modpath::String, cachefile::String)
             if mod == :Main || mod == :Core || mod == :Base
                 continue
             # Module is already loaded
-            elseif isbindingresolved(Main, mod)
+            elseif root_module_exists(mod)
                 continue
             end
             name = string(mod)

base/pkg/entry.jl

@@ -539,7 +539,7 @@ function resolve(
                 info("$(up)grading $pkg: v$ver1 => v$ver2")
                 Write.update(pkg, Read.sha1(pkg,ver2))
                 pkgsym = Symbol(pkg)
-                if Base.isbindingresolved(Main, pkgsym) && isa(getfield(Main, pkgsym), Module)
+                if Base.root_module_exists(pkgsym)
                     push!(imported, "- $pkg")
                 end
             end

base/reflection.jl

@@ -56,13 +56,17 @@ julia> fullname(Main)
 ```
 """
 function fullname(m::Module)
-    m === Main && return ()
-    m === Base && return (:Base,)  # issue #10653
     mn = module_name(m)
+    if m === Main || m === Base || m === Core
+        return (mn,)
+    end
     mp = module_parent(m)
     if mp === m
-        # not Main, but is its own parent, means a prior Main module
-        n = ()
+        if mn !== :Main
+            return (mn,)
+        end
+        # top-level module, not Main, called :Main => prior Main module
+        n = (:Main,)
         this = Main
         while this !== m
             if isdefined(this, :LastMain)
@@ -530,15 +534,22 @@ function _subtypes(m::Module, x::Union{DataType,UnionAll},
     end
     return sts
 end
-function subtypes(m::Module, x::Union{DataType,UnionAll})
-    if isabstract(x)
-        sort!(collect(_subtypes(m, x)), by=string)
-    else
+
+function _subtypes_in(mods::Array, x::Union{DataType,UnionAll})
+    if !isabstract(x)
         # Fast path
-        Union{DataType,UnionAll}[]
+        return Union{DataType,UnionAll}[]
+    end
+    sts = Set{Union{DataType,UnionAll}}()
+    visited = Set{Module}()
+    for m in mods
+        _subtypes(m, x, sts, visited)
     end
+    return sort!(collect(sts), by=string)
 end
 
+subtypes(m::Module, x::Union{DataType,UnionAll}) = _subtypes_in([m], x)
+
 """
     subtypes(T::DataType)
 
@@ -555,7 +566,7 @@ julia> subtypes(Integer)
  Unsigned
 ```
 """
-subtypes(x::Union{DataType,UnionAll}) = subtypes(Main, x)
+subtypes(x::Union{DataType,UnionAll}) = _subtypes_in(loaded_modules_array(), x)
 
 function to_tuple_type(@nospecialize(t))
     @_pure_meta

base/serialize.jl

@@ -347,9 +347,10 @@ function serialize(s::AbstractSerializer, d::Dict)
 end
 
 function serialize_mod_names(s::AbstractSerializer, m::Module)
-    p = module_parent(m)
-    if m !== p
-        serialize_mod_names(s, p)
+    if Base.is_root_module(m)
+        serialize(s, Base.root_module_key(m))
+    else
+        serialize_mod_names(s, module_parent(m))
         serialize(s, module_name(m))
     end
 end
@@ -820,21 +821,25 @@ function deserialize_svec(s::AbstractSerializer)
 end
 
 function deserialize_module(s::AbstractSerializer)
-    path = deserialize(s)
-    m = Main
-    if isa(path,Tuple) && path !== ()
-        # old version
-        for mname in path
-            m = getfield(m,mname)::Module
+    mkey = deserialize(s)
+    if isa(mkey, Tuple)
+        # old version, TODO: remove
+        if mkey === ()
+            return Main
+        end
+        m = Base.root_module(mkey[1])
+        for i = 2:length(mkey)
+            m = getfield(m, mkey[i])::Module
         end
     else
-        mname = path
+        m = Base.root_module(mkey)
+        mname = deserialize(s)
         while mname !== ()
-            m = getfield(m,mname)::Module
+            m = getfield(m, mname)::Module
             mname = deserialize(s)
         end
     end
-    m
+    return m
 end
 
 function deserialize(s::AbstractSerializer, ::Type{Method})

base/show.jl

@@ -380,8 +380,8 @@ function show(io::IO, p::Pair)
 end
 
 function show(io::IO, m::Module)
-    if m === Main
-        print(io, "Main")
+    if is_root_module(m)
+        print(io, module_name(m))
     else
         print(io, join(fullname(m),"."))
     end

doc/src/devdocs/require.md

@@ -26,15 +26,7 @@ The callback below is an example of how to do that:
 ```julia
 # Get the fully-qualified name of a module.
 function module_fqn(name::Symbol)
-    fqn = Symbol[name]
-    mod = getfield(Main, name)
-    parent = Base.module_parent(mod)
-    while parent !== Main
-        push!(fqn, Base.module_name(parent))
-        parent = Base.module_parent(parent)
-    end
-    fqn = reverse!(fqn)
+    fqn = fullname(Base.root_module(name))
     return join(fqn, '.')
 end
 ```
-