Fix and test special loading support for Compiler (JuliaLang#56535)

The new `Compiler` package has a special stub that bypasses compilig a
separate copy if you have `dev`'ed the version that's already compiled
into the sysimg. It wasn't quite working properly in the final version
of that PR if a compiler so loaded was a dependency of another
precompiled package. Fix that and add a test to make sure it doesn't
regress.

Author: Keno

src/Compiler.jl

@@ -6,13 +6,13 @@
 # the system image and simply returns that copy of the compiler. If not,
 # we proceed to load/precompile this as an ordinary package.
 if isdefined(Base, :generating_output) && Base.generating_output(true) &&
-        Base.samefile(Base._compiler_require_dependencies[1][2], @eval @__FILE__) &&
+        Base.samefile(joinpath(Sys.BINDIR, Base.DATAROOTDIR, Base._compiler_require_dependencies[1][2]), @eval @__FILE__) &&
         !Base.any_includes_stale(
-            map(Base.CacheHeaderIncludes, Base._compiler_require_dependencies),
+            map(Base.compiler_chi, Base._compiler_require_dependencies),
             "sysimg", nothing)
 
     Base.prepare_compiler_stub_image!()
-    append!(Base._require_dependencies, Base._compiler_require_dependencies)
+    append!(Base._require_dependencies, map(Base.expand_compiler_path, Base._compiler_require_dependencies))
     # There isn't much point in precompiling native code - downstream users will
     # specialize their own versions of the compiler code and we don't activate
     # the compiler by default anyway, so let's save ourselves some disk space.

test/CompilerLoadingTest/Manifest.toml

@@ -0,0 +1,16 @@
+# This file is machine-generated - editing it directly is not advised
+
+julia_version = "1.12.0-DEV"
+manifest_format = "2.0"
+project_hash = "10c2816629fed766649b89eb6670e7001df6ea18"
+
+[[deps.Compiler]]
+path = "../.."
+uuid = "807dbc54-b67e-4c79-8afb-eafe4df6f2e1"
+version = "0.0.1"
+
+[[deps.CompilerLoadingTest]]
+deps = ["Compiler"]
+path = "."
+uuid = "95defb8a-f82d-44d7-b2c9-37d658f648c1"
+version = "0.0.0"

test/CompilerLoadingTest/Project.toml

@@ -0,0 +1,5 @@
+name = "CompilerLoadingTest"
+uuid = "95defb8a-f82d-44d7-b2c9-37d658f648c1"
+
+[deps]
+Compiler = "807dbc54-b67e-4c79-8afb-eafe4df6f2e1"

test/CompilerLoadingTest/compiler_loading_test.jl

@@ -0,0 +1,12 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+using Test, UUIDs
+
+# This file is loaded as part of special_loading.jl
+Base.compilecache(Base.PkgId(UUID(0x95defb8a_f82d_44d7_b2c9_37d658f648c1), "CompilerLoadingTest"))
+
+using CompilerLoadingTest
+@test Base.maybe_loaded_precompile(Base.PkgId(UUID(0x807dbc54_b67e_4c79_8afb_eafe4df6f2e1), "Compiler"), Base.module_build_id(Base.Compiler)) !== nothing
+
+using Compiler
+@test CompilerLoadingTest.Compiler === Compiler === Base.Compiler

test/CompilerLoadingTest/src/CompilerLoadingTest.jl

@@ -0,0 +1,5 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+module CompilerLoadingTest
+    using Compiler
+end

test/irutils.jl

@@ -1,3 +1,5 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
 using Core.IR
 using Core.Compiler: IRCode, IncrementalCompact, singleton_type, VarState
 using Base.Meta: isexpr

test/runtests.jl

@@ -2,5 +2,6 @@
 using Test, Compiler
 
 for file in readlines(joinpath(@__DIR__, "testgroups"))
+    file == "special_loading" && continue # Only applicable to Base.Compiler
     include(file * ".jl")
 end

test/special_loading.jl

@@ -0,0 +1,9 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+mktempdir() do dir
+    withenv("JULIA_DEPOT_PATH" => dir * (Sys.iswindows() ? ";" : ":"), "JULIA_LOAD_PATH" => nothing) do
+        cd(joinpath(@__DIR__, "CompilerLoadingTest")) do
+            @test success(pipeline(`$(Base.julia_cmd()[1]) --startup-file=no --project=. compiler_loading_test.jl`; stdout, stderr))
+        end
+    end
+end

test/testgroups

@@ -14,3 +14,4 @@ newinterp
 ssair
 tarjan
 validation
+special_loading