Look for package name in [extras] for Preferences

base/loading.jl

@@ -1707,7 +1707,8 @@ function srctext_files(f::IO, srctextpos::Int64)
 end
 
 # Test to see if this UUID is mentioned in this `Project.toml`; either as
-# the top-level UUID (e.g. that of the project itself) or as a dependency.
+# the top-level UUID (e.g. that of the project itself), as a dependency,
+# or as a extra for Preferences.
 function get_uuid_name(project::Dict{String, Any}, uuid::UUID)
     uuid_p = get(project, "uuid", nothing)::Union{Nothing, String}
     name = get(project, "name", nothing)::Union{Nothing, String}
@@ -1722,6 +1723,16 @@ function get_uuid_name(project::Dict{String, Any}, uuid::UUID)
             end
         end
     end
+    for subkey in ("deps", "extras")
+        subsection = get(project, subkey, nothing)::Union{Nothing, Dict{String, Any}}
+        if subsection !== nothing
+            for (k, v) in subsection
+                if uuid == UUID(v::String)
+                    return k
+                end
+            end
+        end
+    end
     return nothing
 end
 

test/loading.jl

@@ -178,6 +178,42 @@ end
     end
 end
 
+# extras
+@testset "extras" begin
+    mktempdir() do dir
+        project_file = joinpath(dir, "Project.toml")
+        touch(project_file) # dummy_uuid calls realpath
+        # various UUIDs to work with
+        proj_uuid = dummy_uuid(project_file)
+        root_uuid = uuid4()
+        this_uuid = uuid4()
+
+        old_load_path = copy(LOAD_PATH)
+        try
+            copy!(LOAD_PATH, [project_file])
+            write(project_file, """
+            name = "Root"
+            uuid = "$root_uuid"
+            [extras]
+            This = "$this_uuid"
+            """)
+            # look up various packages by name
+            root = Base.identify_package("Root")
+            this = Base.identify_package("This")
+            that = Base.identify_package("That")
+
+            @test root.uuid == root_uuid
+            @test this == nothing
+            @test that == nothing
+
+            @test Base.get_uuid_name(project_file, this_uuid) == "This"
+        finally
+            copy!(LOAD_PATH, old_load_path)
+        end
+    end
+end
+
+
 ## functional testing of package identification, location & loading ##
 
 saved_load_path = copy(LOAD_PATH)