[REPL] more reliable extension loading (#58415)

A weird edge case of loading, if REPL is loaded explicitly and does not
come from a require_stdlib call, it should not be getting REPLExt from a
require_stdlib call either. This is a convoluted bit of hackery specific
to work around problems with the way Pkg's REPLExt is designed to mutate
the REPL in unsafe ways. No other stdlib should ever want to access an
extension, particularly of a different module, as that is a private API
violation on multiple counts, so this only needs to be made to work
specifically for that REPL-Pkg scenario, even if it looks seemingly more
general.

Refs #58373

Reproducer:
```
JULIA_DEPOT_PATH=tmpdir/.julia ./julia --hist=no -qie 'using REPL'
] status
```

Author: vtjnash

base/loading.jl

@@ -2715,7 +2715,7 @@ end
 
 # load a serialized file directly from append_bundled_depot_path for uuidkey without stalechecks
 """
-    require_stdlib(package_uuidkey::PkgId, ext::Union{Nothing, String}=nothing)
+    require_stdlib(package_uuidkey::PkgId, [ext::String, from::Module])
 
 !!! warning "May load duplicate copies of stdlib packages."
 
@@ -2754,7 +2754,8 @@ end
       [1] https://github.com/JuliaLang/Pkg.jl/issues/4017#issuecomment-2377589989
       [2] https://github.com/JuliaLang/StyledStrings.jl/issues/91#issuecomment-2379602914
 """
-function require_stdlib(package_uuidkey::PkgId, ext::Union{Nothing, String}=nothing)
+require_stdlib(package_uuidkey::PkgId) = require_stdlib(package_uuidkey, nothing, Base)
+function require_stdlib(package_uuidkey::PkgId, ext::Union{Nothing, String}, from::Module)
     if generating_output(#=incremental=#true)
         # Otherwise this would lead to awkward dependency issues by loading a package that isn't in the Project/Manifest
         error("This interactive function requires a stdlib to be loaded, and package code should instead use it directly from that stdlib.")
@@ -2766,15 +2767,29 @@ function require_stdlib(package_uuidkey::PkgId, ext::Union{Nothing, String}=noth
     newm = start_loading(this_uuidkey, UInt128(0), true)
     newm === nothing || return newm
     try
-        # first since this is a stdlib, try to look there directly first
-        if ext === nothing
-            sourcepath = normpath(env, this_uuidkey.name, "src", this_uuidkey.name * ".jl")
-        else
-            sourcepath = find_ext_path(normpath(joinpath(env, package_uuidkey.name)), ext)
-        end
         depot_path = append_bundled_depot_path!(empty(DEPOT_PATH))
-        set_pkgorigin_version_path(this_uuidkey, sourcepath)
-        newm = _require_search_from_serialized(this_uuidkey, sourcepath, UInt128(0), false; DEPOT_PATH=depot_path)
+        from_stdlib = true # set to false if `from` is a normal package so we do not want the internal loader for the extension either
+        if ext isa String
+            from_uuid = PkgId(from)
+            from_m = get(loaded_modules, from_uuid, nothing)
+            if from_m === from
+                # if from_uuid is either nothing or points to something else, assume we should use require_stdlib
+                # otherwise check cachepath for from to see if it looks like it is from depot_path, since try_build_ids
+                cachepath = get(PkgOrigin, pkgorigins, from_uuid).cachepath
+                entrypath, entryfile = cache_file_entry(from_uuid)
+                from_stdlib = any(x -> startswith(entrypath, x), depot_path)
+            end
+        end
+        if from_stdlib
+            # first since this is a stdlib, try to look there directly first
+            if ext === nothing
+                sourcepath = normpath(env, this_uuidkey.name, "src", this_uuidkey.name * ".jl")
+            else
+                sourcepath = find_ext_path(normpath(joinpath(env, package_uuidkey.name)), ext)
+            end
+            set_pkgorigin_version_path(this_uuidkey, sourcepath)
+            newm = _require_search_from_serialized(this_uuidkey, sourcepath, UInt128(0), false; DEPOT_PATH=depot_path)
+        end
     finally
         end_loading(this_uuidkey, newm)
     end
@@ -2784,10 +2799,12 @@ function require_stdlib(package_uuidkey::PkgId, ext::Union{Nothing, String}=noth
         run_package_callbacks(this_uuidkey)
     else
         # if the user deleted their bundled depot, next try to load it completely normally
+        # if it is an extension, we first need to indicate where to find its parant via EXT_PRIMED
+        ext isa String && (EXT_PRIMED[this_uuidkey] = PkgId[package_uuidkey])
         newm = _require_prelocked(this_uuidkey)
     end
     return newm
-    end
+    end # release lock
 end
 
 # relative-path load

stdlib/REPL/src/Pkg_beforeload.jl

@@ -1,7 +1,9 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
 ## Pkg stuff needed before Pkg has loaded
 
 const Pkg_pkgid = Base.PkgId(Base.UUID("44cfe95a-1eb2-52ea-b672-e2afdf69b78f"), "Pkg")
-load_pkg() = Base.require_stdlib(Pkg_pkgid, "REPLExt")
+load_pkg() = Base.require_stdlib(Pkg_pkgid, "REPLExt", REPL)
 
 ## Below here copied/tweaked from Pkg Types.jl so that the dummy Pkg prompt
 # can populate the env correctly before Pkg loads