Prevent pre-compilation package from triggering its own extensions (#56666)

It is possible for an extension `ExtAB` to be loadable by one of its
triggers, e.g. if `A` loads `B`. However, this loading is not supposed
to happen during pre-compilation of `A`.

Getting this wrong means disagreeing with the scheduled pre-compile jobs
(`A` is not scheduled to depend on or generate a cache file for `ExtAB`
but accidentally attempts both) and leads to confusing errors about
missing cache files.

We used to cover up this bad behavior w/ an erroneous cycle warning
(fixed by #55910), but now we need to be sure this works.

Author: topolarity

base/loading.jl

@@ -1215,6 +1215,7 @@ function run_module_init(mod::Module, i::Int=1)
 end
 
 function run_package_callbacks(modkey::PkgId)
+    (modkey == precompilation_target) && return nothing
     run_extension_callbacks(modkey)
     assert_havelock(require_lock)
     unlock(require_lock)
@@ -1338,7 +1339,7 @@ function _insert_extension_triggers(parent::PkgId, extensions::Dict{String, Any}
             # TODO: Better error message if this lookup fails?
             uuid_trigger = UUID(totaldeps[trigger]::String)
             trigger_id = PkgId(uuid_trigger, trigger)
-            if !haskey(Base.loaded_modules, trigger_id) || haskey(package_locks, trigger_id)
+            if !haskey(Base.loaded_modules, trigger_id) || haskey(package_locks, trigger_id) || (trigger_id == precompilation_target)
                 trigger1 = get!(Vector{ExtensionId}, EXT_DORMITORY, trigger_id)
                 push!(trigger1, gid)
             else
@@ -1350,6 +1351,7 @@ end
 
 loading_extension::Bool = false
 precompiling_extension::Bool = false
+precompilation_target::Union{Nothing,PkgId} = nothing
 function run_extension_callbacks(extid::ExtensionId)
     assert_havelock(require_lock)
     succeeded = try
@@ -2342,6 +2344,7 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, output_o::
     write(io.in, """
         empty!(Base.EXT_DORMITORY) # If we have a custom sysimage with `EXT_DORMITORY` prepopulated
         Base.precompiling_extension = $(loading_extension)
+        Base.precompilation_target = $(pkg_str(pkg))
         Base.include_package_for_output($(pkg_str(pkg)), $(repr(abspath(input))), $(repr(depot_path)), $(repr(dl_load_path)),
             $(repr(load_path)), $deps, $(repr(source_path(nothing))))
         """)

test/loading.jl

@@ -1101,6 +1101,41 @@ end
             cmd_proj_ext = addenv(cmd_proj_ext, "JULIA_LOAD_PATH" => join([joinpath(proj, "HasExtensions.jl"), joinpath(proj, "EnvWithDeps")], sep))
             run(cmd_proj_ext)
         end
+
+        # Extensions for "parent" dependencies
+        # (i.e. an `ExtAB`  where A depends on / loads B, but B provides the extension)
+
+        mktempdir() do depot # Parallel pre-compilation
+            code = """
+            Base.disable_parallel_precompile = false
+            using Parent
+            Base.get_extension(getfield(Parent, :DepWithParentExt), :ParentExt) isa Module || error("expected extension to load")
+            Parent.greet()
+            """
+            proj = joinpath(@__DIR__, "project", "Extensions", "Parent.jl")
+            cmd =  `$(Base.julia_cmd()) --startup-file=no -e $code`
+            cmd = addenv(cmd,
+                "JULIA_LOAD_PATH" => proj,
+                "JULIA_DEPOT_PATH" => depot * Base.Filesystem.pathsep(),
+            )
+            @test occursin("Hello parent!", String(read(cmd)))
+        end
+        mktempdir() do depot # Serial pre-compilation
+            code = """
+            Base.disable_parallel_precompile = true
+            using Parent
+            Base.get_extension(getfield(Parent, :DepWithParentExt), :ParentExt) isa Module || error("expected extension to load")
+            Parent.greet()
+            """
+            proj = joinpath(@__DIR__, "project", "Extensions", "Parent.jl")
+            cmd =  `$(Base.julia_cmd()) --startup-file=no -e $code`
+            cmd = addenv(cmd,
+                "JULIA_LOAD_PATH" => proj,
+                "JULIA_DEPOT_PATH" => depot * Base.Filesystem.pathsep(),
+            )
+            @test occursin("Hello parent!", String(read(cmd)))
+        end
+
     finally
         try
             rm(depot_path, force=true, recursive=true)

test/project/Extensions/DepWithParentExt.jl/Project.toml

@@ -0,0 +1,9 @@
+name = "DepWithParentExt"
+uuid = "8a35c396-5ffc-40d2-b7ec-e8ed2248da32"
+version = "0.1.0"
+
+[weakdeps]
+Parent = "58cecb9c-f68a-426e-b92a-89d456ae7acc"
+
+[extensions]
+ParentExt = "Parent"

test/project/Extensions/DepWithParentExt.jl/ext/ParentExt.jl

@@ -0,0 +1,6 @@
+module ParentExt
+
+using Parent
+using DepWithParentExt
+
+end

test/project/Extensions/DepWithParentExt.jl/src/DepWithParentExt.jl

@@ -0,0 +1,5 @@
+module DepWithParentExt
+
+greet() = print("Hello dep w/ ext for parent dep!")
+
+end # module DepWithParentExt

test/project/Extensions/Parent.jl/Manifest.toml

@@ -0,0 +1,16 @@
+# This file is machine-generated - editing it directly is not advised
+
+julia_version = "1.10.6"
+manifest_format = "2.0"
+project_hash = "5d72c155f50f076d28b74de819d417878ffb0965"
+
+[[deps.DepWithParentExt]]
+path = "../DepWithParentExt.jl"
+uuid = "8a35c396-5ffc-40d2-b7ec-e8ed2248da32"
+version = "0.1.0"
+
+    [deps.DepWithParentExt.extensions]
+    ParentExt = "Parent"
+
+    [deps.DepWithParentExt.weakdeps]
+    Parent = "58cecb9c-f68a-426e-b92a-89d456ae7acc"

test/project/Extensions/Parent.jl/Project.toml

@@ -0,0 +1,6 @@
+name = "Parent"
+uuid = "58cecb9c-f68a-426e-b92a-89d456ae7acc"
+version = "0.1.0"
+
+[deps]
+DepWithParentExt = "8a35c396-5ffc-40d2-b7ec-e8ed2248da32"

test/project/Extensions/Parent.jl/src/Parent.jl

@@ -0,0 +1,7 @@
+module Parent
+
+using DepWithParentExt
+
+greet() = print("Hello parent!")
+
+end # module Parent