From 63e95d47e692352fac5541b6ee835b573f4c4898 Mon Sep 17 00:00:00 2001
From: Ian Butterworth <i.r.butterworth@gmail.com>
Date: Fri, 9 Feb 2024 02:34:34 -0500
Subject: [PATCH] Add nested precomp highlight debug (#53111)

---
 base/loading.jl | 13 +++++++++++++
 pkgimage.mk     |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/base/loading.jl b/base/loading.jl
index 34d1e848ecb98..d18d4e72ae809 100644
--- a/base/loading.jl
+++ b/base/loading.jl
@@ -2508,6 +2508,7 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, output_o::
     # write data over stdin to avoid the (unlikely) case of exceeding max command line size
     write(io.in, """
         empty!(Base.EXT_DORMITORY) # If we have a custom sysimage with `EXT_DORMITORY` prepopulated
+        Base.track_nested_precomp($(vcat(Base.precompilation_stack, pkg)))
         Base.precompiling_extension = $(loading_extension)
         Base.include_package_for_output($(pkg_str(pkg)), $(repr(abspath(input))), $(repr(depot_path)), $(repr(dl_load_path)),
             $(repr(load_path)), $deps, $(repr(source_path(nothing))))
@@ -2516,6 +2517,18 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, output_o::
     return io
 end
 
+const precompilation_stack = Vector{PkgId}()
+# Helpful for debugging when precompilation is unexpectedly nested.
+# Enable with `JULIA_DEBUG=nested_precomp`. Note that it expected to be nested in classical code-load precompilation
+# TODO: Add detection if extension precompilation is nested and error / return early?
+function track_nested_precomp(pkgs::Vector{PkgId})
+    append!(precompilation_stack, pkgs)
+    if length(precompilation_stack) > 1
+        list() = join(map(p->p.name, precompilation_stack), " > ")
+        @debug "Nested precompilation: $(list())" _group=:nested_precomp
+    end
+end
+
 function compilecache_dir(pkg::PkgId)
     entrypath, entryfile = cache_file_entry(pkg)
     return joinpath(DEPOT_PATH[1], entrypath)
diff --git a/pkgimage.mk b/pkgimage.mk
index 9a46a8d581bf8..b45b4ab89560b 100644
--- a/pkgimage.mk
+++ b/pkgimage.mk
@@ -69,6 +69,9 @@ cache-debug-$1: $$(BUILDDIR)/stdlib/$1.debug.image
 .SECONDARY: $$(BUILDDIR)/stdlib/$1.release.image $$(BUILDDIR)/stdlib/$1.debug.image
 endef
 
+# Note: you can check for the correctness of this tree by running `JULIA_DEBUG=nested_precomp make` and looking
+# out for `Debug: Nested precompilation` logs.
+
 # no dependencies
 $(eval $(call stdlib_builder,MozillaCACerts_jll,))
 $(eval $(call stdlib_builder,ArgTools,))