Crystal: debug codegen failures

debug_codegen_failures.patch

diff --git a/src/compiler/crystal/compiler.cr b/src/compiler/crystal/compiler.cr
index 38880ee9e..966e2f954 100644
--- a/src/compiler/crystal/compiler.cr
+++ b/src/compiler/crystal/compiler.cr
@@ -523,13 +523,17 @@ module Crystal
     private def fork_codegen(units, n_threads)
       workers = fork_workers(n_threads) do |input, output|
         while i = input.gets(chomp: true).presence
+          Crystal::System.print_error "CODEGEN pid=#{LibC.getpid} STDIN => #{i}\n"
           unit = units[i.to_i]
+          Crystal::System.print_error "CODEGEN pid=#{LibC.getpid} COMPILE unit.name=#{unit.name}\n"
           unit.compile
           result = {name: unit.name, reused: unit.reused_previous_compilation?}
+          Crystal::System.print_error "CODEGEN pid=#{LibC.getpid} STDOUT <= #{result.to_json}\n"
           output.puts result.to_json
         end
       rescue ex
         result = {exception: {name: ex.class.name, message: ex.message, backtrace: ex.backtrace}}
+        Crystal::System.print_error "CODEGEN pid=#{LibC.getpid} EXCEPTION #{ex.inspect_with_backtrace}\n"
         output.puts result.to_json
       end
 
@@ -539,32 +543,35 @@ module Crystal
       completed = Channel(Nil).new(n_threads)
 
       workers.each do |pid, input, output|
-        spawn do
+        spawn(name: "codegen-#{pid}") do
           overqueued = 0
 
           overqueue.times do
             if (index = indexes.add(1)) < units.size
+              Crystal::System.print_error "MAIN => #{pid} STDIN <= #{index}\n"
               input.puts index
               overqueued += 1
             end
           end
 
           while (index = indexes.add(1)) < units.size
+            Crystal::System.print_error "MAIN => #{pid} STDIN <= #{index}\n"
             input.puts index
 
             if response = output.gets(chomp: true)
               channel.send response
             else
-              Crystal::System.print_error "\nBUG: a codegen process failed\n"
+              Crystal::System.print_error "\nBUG: a codegen process exited early\n"
               exit 1
             end
           end
 
           overqueued.times do
             if response = output.gets(chomp: true)
+              Crystal::System.print_error "MAIN => #{pid} STDOUT => #{response}\n"
               channel.send response
             else
-              Crystal::System.print_error "\nBUG: a codegen process failed\n"
+              Crystal::System.print_error "\nBUG: a codegen process exited early\n"
               exit 1
             end
           end
@@ -574,11 +581,12 @@ module Crystal
           output.close
 
           Process.new(pid).wait
+        ensure
           completed.send(nil)
         end
       end
 
-      spawn do
+      spawn(name: "codegen-waiter") do
         n_threads.times { completed.receive }
         channel.close
       end