Further refine our debugging infrastructure

.gitignore

@@ -62,3 +62,5 @@ _coverage/
 
 # Debugger support
 ocamlc
+ocamlopt
+.ocamldebug

HACKING.md

@@ -206,21 +206,23 @@ something like:
 
 ## Using the OCaml debugger to debug the compiler
 
-First, run `make debug`. This completes three steps:
+First, run `make debug`. This completes four steps:
 
 1. `make install`
 2. Sets up the `ocaml/tools/debug_printers` script so that you can `source
    ocaml/tools/debug_printers` during a debugging session to see
-   otherwise-abstract variable values.  This script is automatically loaded by
-   the debugger due to the `.ocamldebug` file at the root of the compiler repo.
+   otherwise-abstract variable values.
 3. Symlinks `./ocamlc` and `./ocamlopt` to point to the bytecode versions of
    those compilers. This is convenient for emacs integration, because emacs
    looks for sources starting in the directory containing the executable.
+4. Creates a `.ocamldebug` file to automatically load the right search path
+   and the `debug_printers` set up above.
 
 Then it's time to run the debugger itself.  The recommended workflow is to add
 the elisp below to your emacs init file, and then use the command
 `ocamldebug-ocamlc` to debug `ocamlc` or the command `ocamldebug-ocamlopt` to
-debug `ocamlopt`.
+debug `ocamlopt`. Running your built `ocamldebug` file on `ocamlc` or `ocamlopt`
+should also work, if you wish to work outside emacs.
 
 ```
 ;; directly inspired by the ocamldebug implementation in ocamldebug.el
@@ -243,6 +245,9 @@ debug `ocamlopt`.
       (setq ocamldebug-debuggee-args
             (read-from-minibuffer (format "Args for ocamlc: ")
                                   ocamldebug-debuggee-args))
+      ;; In addition to the directories in .ocamldebug, use 'find' to
+      ;; see also list directories with -I; this finds any new cmo directories
+      ;; since the last 'make debug'
       (let* ((cmo-top-dir (file-name-concat ocaml-dir "_build/main"))
              (find-cmo-cmd (concat "find "
                                    cmo-top-dir

Makefile

@@ -163,17 +163,14 @@ coverage: boot-runtest
 
 .PHONY: debug
 .NOTPARALLEL: debug
-debug: install ocaml/tools/debug_printers ocamlc ocamlopt
+debug: install debug-printers ocamlc ocamlopt .ocamldebug
 
 ocamlc:
 	ln -s $(prefix)/bin/ocamlc.byte ocamlc
 
 ocamlopt:
 	ln  -s $(prefix)/bin/ocamlopt.byte ocamlopt
 
-ocaml/tools/debug_printers: ocaml/tools/debug_printers.ml ocaml/tools/debug_printers.cmo
-	echo 'load_printer "ocaml/tools/debug_printers.cmo"' > $@
-	awk '{ print "install_printer Debug_printers." $$2 }' < $< >> $@
-
-ocaml/tools/debug_printers.cmo: ocaml/tools/debug_printers.ml _build/install/main/bin/ocamlc.byte
-	_build/install/main/bin/ocamlc.byte -c -I _build/main/ocaml/.ocamlcommon.objs/byte ocaml/tools/debug_printers.ml
+.ocamldebug: install
+	find _build/main -name '*.cmo' -type f -printf 'directory %h\n' | sort -u > .ocamldebug
+	echo "source ocaml/tools/debug_printers" >> .ocamldebug

ocaml/tools/dune

@@ -91,4 +91,16 @@
   (libraries ocamlcommon)
   (modules debug_printers))
 
+(rule
+  (target debug_printers)
+  (deps debug_printers.ml %{cmo:debug_printers})
+  (action
+    (with-stdout-to %{target}
+      (progn
+        ; Resorting to Bash instead of the built-in [echo] action because I
+        ; couldn't find a better way to get an absolute path out of Dune
+        (bash "echo load_printer \\\"$(realpath %{cmo:debug_printers})\\\"")
+        (with-stdin-from debug_printers.ml
+          (run awk "{ print \"install_printer Debug_printers.\" $2 }"))))))
+
 ; ocamlcp, ocamloptp and ocamlprof are not currently supported.