Nospecialize close(c::Channel, excp::Exception) on excp. (JuliaLang#49508)

* Nospecialize close(c::Channel, excp::Exception) on excp.

Fixes JuliaLang#49507.

Avoids dynamic dispatch when closing a Channel with an Exception, and
should avoid a call into the runtime for julia compilation when
attempting to report an exception.

* Add test for this case.

Author: NHDaly

base/channels.jl

@@ -183,7 +183,8 @@ Close a channel. An exception (optionally given by `excp`), is thrown by:
 * [`put!`](@ref) on a closed channel.
 * [`take!`](@ref) and [`fetch`](@ref) on an empty, closed channel.
 """
-function close(c::Channel, excp::Exception=closed_exception())
+close(c::Channel) = close(c, closed_exception()) # nospecialize on default arg seems to confuse makedocs
+function close(c::Channel, @nospecialize(excp::Exception))
     lock(c)
     try
         c.excp = excp

test/channels.jl

@@ -619,3 +619,20 @@ end
         @test n_avail(c) == 0
     end
 end
+
+# Issue #49507: stackoverflow in type inference caused by close(::Channel, ::Exception)
+@testset "close(::Channel, ::StackOverflowError)" begin
+    ch = let result = Channel()
+        foo() = try
+            foo()
+        catch e;
+            close(result, e)
+        end
+
+        foo()  # This shouldn't fail with an internal stackoverflow error in inference.
+
+        result
+    end
+
+    @test (try take!(ch) catch e; e; end) isa StackOverflowError
+end