Teach detect_{libgfortran,libstdcxx}_version to deal with lazy CSL

We can no longer depend on the fact that these libraries will be eagerly
loaded (huzzah!) so we must teach these helper functions to either
inspect the lazy CSL JLL for the necessary information, or just directly
load the library.

Author: staticfloat

base/Base.jl

@@ -213,9 +213,6 @@ using .PermutedDimsArrays
 include("sort.jl")
 using .Sort
 
-# BinaryPlatforms, used by Artifacts.  Needs `Sort`.
-include("binaryplatforms.jl")
-
 # Fast math
 include("fastmath.jl")
 using .FastMath
@@ -269,6 +266,9 @@ include("linking.jl")
 include("staticdata.jl")
 include("loading.jl")
 
+# BinaryPlatforms, used by Artifacts.  Needs `Sort`.
+include("binaryplatforms.jl")
+
 # misc useful functions & macros
 include("timing.jl")
 include("client.jl")

base/binaryplatforms.jl

@@ -841,20 +841,48 @@ function parse_dl_name_version(path::AbstractString, os::AbstractString)
     return parse_dl_name_version(string(path)::String, string(os)::String)
 end
 
+function get_csl_member(member::Symbol)
+    # If CompilerSupportLibraries_jll is an stdlib, we can just grab things from it
+    csl_pkgids = filter(pkgid -> pkgid.name == "CompilerSupportLibraries_jll", keys(Base.loaded_modules))
+    if !isempty(csl_pkgids)
+        CSL_mod = Base.loaded_modules[first(csl_pkgids)]
+
+        # This can fail during bootstrap, so we skip in that case.
+        if isdefined(CSL_mod, member)
+            return getproperty(CSL_mod, member)
+        end
+    end
+
+    return nothing
+end
+
 """
     detect_libgfortran_version()
 
 Inspects the current Julia process to determine the libgfortran version this Julia is
-linked against (if any).
+linked against (if any).  Returns `nothing` if no libgfortran version dependence is
+detected.
 """
 function detect_libgfortran_version()
-    libgfortran_paths = filter!(x -> occursin("libgfortran", x), Libdl.dllist())
-    if isempty(libgfortran_paths)
+    function get_libgfortran_path()
+        # If CompilerSupportLibraries_jll is an stdlib, we can just directly ask for
+        # the path here, without checking `dllist()`:
+        libgfortran_path = get_csl_member(:libgfortran_path)
+        if libgfortran_path !== nothing
+            return libgfortran_path::String
+        end
+
+        # Otherwise, look for it having already been loaded by something
+        libgfortran_paths = filter!(x -> occursin("libgfortran", x), Libdl.dllist())
+        if !isempty(libgfortran_paths)
+            return first(libgfortran_paths)::String
+        end
+
         # One day, I hope to not be linking against libgfortran in base Julia
         return nothing
     end
-    libgfortran_path = first(libgfortran_paths)
 
+    libgfortran_path = get_libgfortran_path()
     name, version = parse_dl_name_version(libgfortran_path, os())
     if version === nothing
         # Even though we complain about this, we allow it to continue in the hopes that
@@ -878,24 +906,37 @@ it is linked against (if any).  `max_minor_version` is the latest version in the
 3.4 series of GLIBCXX where the search is performed.
 """
 function detect_libstdcxx_version(max_minor_version::Int=30)
-    libstdcxx_paths = filter!(x -> occursin("libstdc++", x), Libdl.dllist())
-    if isempty(libstdcxx_paths)
-        # This can happen if we were built by clang, so we don't link against
-        # libstdc++ at all.
+    function get_libstdcxx_handle()
+        # If CompilerSupportLibraries_jll is an stdlib, we can just directly open it
+        libstdcxx = get_csl_member(:libstdcxx)
+        if libstdcxx !== nothing
+            return nothing
+        end
+
+        # Otherwise, look for it having already been loaded by something
+        libstdcxx_paths = filter!(x -> occursin("libstdc++", x), Libdl.dllist())
+        if !isempty(libstdcxx_paths)
+            return Libdl.dlopen(first(libstdcxx_paths), Libdl.RTLD_NOLOAD)::Ptr{Cvoid}
+        end
+
+        # One day, I hope to not be linking against libgfortran in base Julia
         return nothing
     end
 
     # Brute-force our way through GLIBCXX_* symbols to discover which version we're linked against
-    hdl = Libdl.dlopen(first(libstdcxx_paths))::Ptr{Cvoid}
-    # Try all GLIBCXX versions down to GCC v4.8:
-    # https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html
-    for minor_version in max_minor_version:-1:18
-        if Libdl.dlsym(hdl, "GLIBCXX_3.4.$(minor_version)"; throw_error=false) !== nothing
-            Libdl.dlclose(hdl)
-            return VersionNumber("3.4.$(minor_version)")
+    libstdcxx = get_libstdcxx_handle()
+
+    if libstdcxx !== nothing
+        # Try all GLIBCXX versions down to GCC v4.8:
+        # https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html
+        for minor_version in max_minor_version:-1:18
+            if Libdl.dlsym(libstdcxx, "GLIBCXX_3.4.$(minor_version)"; throw_error=false) !== nothing
+                Libdl.dlclose(libstdcxx)
+                return VersionNumber("3.4.$(minor_version)")
+            end
         end
     end
-    Libdl.dlclose(hdl)
+    Libdl.dlclose(libstdcxx)
     return nothing
 end