Warn about cycles in extension precompilation

base/loading.jl

@@ -1498,6 +1498,12 @@ function run_extension_callbacks(pkgid::PkgId)
         if extid.ntriggers == 0
             # actually load extid, now that all dependencies are met,
             # and record the result
+            if in(extid.id, precompilation_stack)
+                @warn """
+                Dependency cycle detected in extension precompilation: $(precompilation_stack_list()) > $(extid.id.name)
+                Loading $(extid.id.name) here will likely fail.
+                """
+            end
             succeeded = succeeded && run_extension_callbacks(extid)
             succeeded || push!(EXT_DORMITORY_FAILED, extid)
         end
@@ -2842,14 +2848,14 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, output_o::
 end
 
 const precompilation_stack = Vector{PkgId}()
+precompilation_stack_list() = join(map(p->p.name, precompilation_stack), " > ")
 # 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
+        @debug "Nested precompilation: $(precompilation_stack_list())" _group=:nested_precomp
     end
 end
 

test/extensions/circular/A/Project.toml

@@ -0,0 +1,14 @@
+name = "A"
+uuid = "c8938445-7efa-411c-ba8f-721576f9f47a"
+version = "0.1.0"
+
+[deps]
+B = "ef00b25e-dd85-47e0-9cd9-ed3c1ff51032"
+
+[weakdeps]
+C = "d95b043b-fbe6-48a2-93d2-75fba1b51518"
+D = "64e66ba5-e914-4adb-a5f6-036ef0c801f3"
+
+[extensions]
+CExt = "C"
+DExt = "D"

test/extensions/circular/A/ext/CExt.jl

@@ -0,0 +1,3 @@
+module CExt
+
+end # module

test/extensions/circular/A/ext/DExt.jl

@@ -0,0 +1,3 @@
+module DExt
+
+end # module

test/extensions/circular/A/src/A.jl

@@ -0,0 +1,3 @@
+module A
+
+end # module

test/extensions/circular/B/Project.toml

@@ -0,0 +1,7 @@
+name = "B"
+uuid = "ef00b25e-dd85-47e0-9cd9-ed3c1ff51032"
+version = "0.1.0"
+
+[deps]
+C = "d95b043b-fbe6-48a2-93d2-75fba1b51518"
+D = "64e66ba5-e914-4adb-a5f6-036ef0c801f3"

test/extensions/circular/B/src/B.jl

@@ -0,0 +1,3 @@
+module B
+
+end # module

test/extensions/circular/C/Project.toml

@@ -0,0 +1,3 @@
+name = "C"
+uuid = "d95b043b-fbe6-48a2-93d2-75fba1b51518"
+version = "0.1.0"

test/extensions/circular/C/src/C.jl

@@ -0,0 +1,3 @@
+module C
+
+end # module

test/extensions/circular/D/Project.toml

@@ -0,0 +1,3 @@
+name = "D"
+uuid = "64e66ba5-e914-4adb-a5f6-036ef0c801f3"
+version = "0.1.0"

test/extensions/circular/D/src/D.jl

@@ -0,0 +1,3 @@
+module D
+
+end # module

test/extensions/circular/Manifest.toml

@@ -0,0 +1,32 @@
+# This file is machine-generated - editing it directly is not advised
+
+julia_version = "1.11.0-DEV"
+manifest_format = "2.0"
+project_hash = "6c189c4d9e1e9194c4a4d7627740c379ecff4942"
+
+[[deps.A]]
+deps = ["B"]
+path = "./A"
+uuid = "c8938445-7efa-411c-ba8f-721576f9f47a"
+version = "0.1.0"
+weakdeps = ["C", "D"]
+
+    [deps.A.extensions]
+    CExt = "C"
+    DExt = "D"
+
+[[deps.B]]
+deps = ["C", "D"]
+path = "./B"
+uuid = "ef00b25e-dd85-47e0-9cd9-ed3c1ff51032"
+version = "0.1.0"
+
+[[deps.C]]
+path = "./C"
+uuid = "d95b043b-fbe6-48a2-93d2-75fba1b51518"
+version = "0.1.0"
+
+[[deps.D]]
+path = "./D"
+uuid = "64e66ba5-e914-4adb-a5f6-036ef0c801f3"
+version = "0.1.0"

test/extensions/circular/Project.toml

@@ -0,0 +1,5 @@
+[deps]
+A = "c8938445-7efa-411c-ba8f-721576f9f47a"
+B = "ef00b25e-dd85-47e0-9cd9-ed3c1ff51032"
+C = "d95b043b-fbe6-48a2-93d2-75fba1b51518"
+D = "64e66ba5-e914-4adb-a5f6-036ef0c801f3"

test/loading.jl

@@ -1143,6 +1143,19 @@ end
         finally
             copy!(LOAD_PATH, old_load_path)
         end
+
+        # issue 53081
+        @testset "avoid circular precompilation deadlock through extensions" begin
+            testenv = joinpath(@__DIR__, "extensions", "circular")
+            # TODO: avoid the error? https://github.com/JuliaLang/julia/pull/53112
+            # @test_warn (r"Dependency cycle detected in extension precompilation", r"Error during loading of extension") begin
+                run(ignorestatus(addenv(
+                    `$(Base.julia_cmd()) --startup-file=no --project=$testenv -e 'using A'`,
+                    "JULIA_TESTS" => nothing, # we want precompilepkgs to print for this, which it doesn't if this is set
+                    "JULIA_DEPOT_PATH" => depot_path
+                )))
+            # end
+        end
     finally
         try
             rm(depot_path, force=true, recursive=true)