cl: Phase 3 interactive-debugger — *debugger-hook* pattern, 7 tests (143 total)

cl-debugger-hook global (nil = default), cl-invoke-debugger walks the hook,
cl-error-with-debugger routes unhandled errors through the hook, and
make-policy-debugger builds a hook from a (fn (condition restarts) name)
policy function. Tests: hook receives condition, policy selects use-zero/abort
restarts, compute-restarts visible inside hook, handler wins before hook fires,
infinite-recursion guard. Wired into test.sh program suite runner.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/common-lisp/tests/programs/interactive-debugger.sx

@@ -0,0 +1,196 @@
+;; interactive-debugger.sx — Condition debugger using *debugger-hook*
+;;
+;; Demonstrates the classic CL debugger pattern:
+;;   - *debugger-hook* is invoked when an unhandled error reaches the top level
+;;   - The hook receives the condition and a reference to itself
+;;   - It can offer restarts interactively (here simulated with a policy fn)
+;;
+;; In real CL the debugger reads from the terminal. Here we simulate
+;; the "user input" via a policy function passed in at call time.
+;;
+;; Depends on: lib/common-lisp/runtime.sx already loaded.
+
+;; ── *debugger-hook* global ────────────────────────────────────────────────
+;;
+;; CL: when error is unhandled, invoke *debugger-hook* with (condition hook).
+;; A nil hook means use the system default (which we simulate as re-raise).
+
+(define cl-debugger-hook nil)
+
+;; ── invoke-debugger ────────────────────────────────────────────────────────
+;;
+;; Called when cl-error finds no handler. Tries cl-debugger-hook first;
+;; falls back to a simple error report.
+
+(define
+  cl-invoke-debugger
+  (fn
+    (c)
+    (if
+      (nil? cl-debugger-hook)
+      (error (str "Debugger: " (cl-condition-message c)))
+      (begin
+        (let
+          ((hook cl-debugger-hook))
+          (set! cl-debugger-hook nil)
+          (let
+            ((result (hook c hook)))
+            (set! cl-debugger-hook hook)
+            result))))))
+
+;; ── cl-error/debugger — error that routes through invoke-debugger ─────────
+
+(define
+  cl-error-with-debugger
+  (fn
+    (c &rest args)
+    (let
+      ((obj (cond ((cl-condition? c) c) ((string? c) (cl-make-condition "simple-error" "format-control" c "format-arguments" args)) (:else (cl-make-condition "simple-error" "format-control" (str c))))))
+      (cl-signal-obj obj cl-handler-stack)
+      (cl-invoke-debugger obj))))
+
+;; ── simulated debugger session ────────────────────────────────────────────
+;;
+;; A debugger hook takes (condition hook) and "reads" user commands.
+;; We simulate this with a policy function: (fn (c restarts) restart-name)
+;; that picks a restart given the condition and available restarts.
+
+(define
+  make-policy-debugger
+  (fn
+    (policy)
+    (fn
+      (c hook)
+      (let
+        ((available (cl-compute-restarts)))
+        (let
+          ((choice (policy c available)))
+          (if
+            (and choice (not (nil? (cl-find-restart choice))))
+            (cl-invoke-restart choice)
+            (error
+              (str
+                "Debugger: no restart chosen for: "
+                (cl-condition-message c)))))))))
+
+;; ── tests ─────────────────────────────────────────────────────────────────
+
+(define passed 0)
+(define failed 0)
+(define failures (list))
+
+(define
+  check
+  (fn
+    (label got expected)
+    (if
+      (= got expected)
+      (set! passed (+ passed 1))
+      (begin
+        (set! failed (+ failed 1))
+        (set!
+          failures
+          (append
+            failures
+            (list
+              (str
+                "FAIL ["
+                label
+                "]: got="
+                (inspect got)
+                " expected="
+                (inspect expected)))))))))
+
+(define
+  reset-stacks!
+  (fn
+    ()
+    (set! cl-handler-stack (list))
+    (set! cl-restart-stack (list))
+    (set! cl-debugger-hook nil)))
+
+;; Test 1: debugger hook receives condition
+(reset-stacks!)
+(let
+  ((received-msg ""))
+  (begin
+    (set!
+      cl-debugger-hook
+      (fn (c hook) (set! received-msg (cl-condition-message c)) nil))
+    (cl-restart-case
+      (fn () (cl-error-with-debugger "something broke"))
+      (list "abort" (list) (fn () nil)))
+    (check "debugger hook receives condition" received-msg "something broke")))
+
+;; Test 2: policy-driven restart selection (use-zero)
+(reset-stacks!)
+(let
+  ((result (begin (set! cl-debugger-hook (make-policy-debugger (fn (c restarts) "use-zero"))) (cl-restart-case (fn () (cl-error-with-debugger (cl-make-condition "division-by-zero")) 999) (list "use-zero" (list) (fn () 0))))))
+  (check "policy debugger: use-zero restart" result 0))
+
+;; Test 3: policy selects abort
+(reset-stacks!)
+(let
+  ((result (begin (set! cl-debugger-hook (make-policy-debugger (fn (c restarts) "abort"))) (cl-restart-case (fn () (cl-error-with-debugger "aborting error") 999) (list "abort" (list) (fn () "aborted"))))))
+  (check "policy debugger: abort restart" result "aborted"))
+
+;; Test 4: compute-restarts inside debugger hook
+(reset-stacks!)
+(let
+  ((seen-restarts (list)))
+  (begin
+    (set!
+      cl-debugger-hook
+      (fn
+        (c hook)
+        (set! seen-restarts (cl-compute-restarts))
+        (cl-invoke-restart "continue")))
+    (cl-restart-case
+      (fn () (cl-error-with-debugger "test") 42)
+      (list "continue" (list) (fn () "ok"))
+      (list "abort" (list) (fn () "no")))
+    (check
+      "debugger: compute-restarts visible"
+      (= (len seen-restarts) 2)
+      true)))
+
+;; Test 5: hook not invoked when handler catches first
+(reset-stacks!)
+(let
+  ((hook-called false)
+    (result
+      (begin
+        (set! cl-debugger-hook (fn (c hook) (set! hook-called true) nil))
+        (cl-handler-case
+          (fn () (cl-error-with-debugger "handled"))
+          (list "error" (fn (c) "handler-won"))))))
+  (check "handler wins; hook not called" hook-called false)
+  (check "handler result returned" result "handler-won"))
+
+;; Test 6: debugger-hook nil after re-raise guard
+(reset-stacks!)
+(let
+  ((hook-calls 0))
+  (begin
+    (set!
+      cl-debugger-hook
+      (fn
+        (c hook)
+        (set! hook-calls (+ hook-calls 1))
+        (if
+          (> hook-calls 1)
+          (error "infinite loop guard")
+          (cl-invoke-restart "escape"))))
+    (cl-restart-case
+      (fn () (cl-error-with-debugger "once"))
+      (list "escape" (list) (fn () nil)))
+    (check
+      "hook called exactly once (no infinite recursion)"
+      hook-calls
+      1)))
+
+;; ── summary ────────────────────────────────────────────────────────────────
+
+(define debugger-passed passed)
+(define debugger-failed failed)
+(define debugger-failures failures)