next-error stops on a diagnostic's notes, and CFn is drawn as a type

TODO.org

@@ -1862,10 +1862,12 @@ and a half-loaded file. =C-c C-k= is taken by the inspector.
 so =next-error= works, but a minor mode installs no font-lock. Open: whether the
 program's output should look different from the compiler's.
 
-** TODO compilation-mode steps over the notes
-Nothing sets the skip threshold, so =next-error= walks the errors and steps over
-the notes, which are still parsed, coloured and clickable. Labelling them as
-warnings would make them navigable and is refused: a note is not a warning.
+** DONE compilation-mode steps over the notes
+CLOSED: [2026-09-25]
+The daemon buffer and the diagnostics buffer set =compilation-skip-threshold= to
+0 locally, so =next-error= stops on a note as well as an error. The user's own
+default is left alone. Rules out relabelling a note as a warning to make it
+navigable.
 
 * Docs and the repository
 

emacs/flan-mode.el

@@ -235,8 +235,9 @@ reason and is the odd one — it is legal only as the last item of a `def' or a
     ("\\_<\\([a-zA-Z][a-zA-Z0-9!?*+=<>._-]*/\\)" 1 font-lock-type-face)
     ;; The types the compiler knows without being told: every primitive in
     ;; `Types.primitive_names', plus the four applied ones the checker
-    ;; resolves and the function type.  `dyn' is lowercase on purpose — it is
-    ;; a primitive beside `i64' and `bool', not a container over something.
+    ;; resolves and the two function types, `Fn' and `CFn'.  `dyn' is
+    ;; lowercase on purpose — it is a primitive beside `i64' and `bool', not
+    ;; a container over something.
     ;; `int' and `float' are builtin aliases for `i32' and `f32'.
     ;;
     ;; `Unit' is deliberately absent, though `Types.primitive_names' has it.
@@ -245,7 +246,7 @@ reason and is the odd one — it is legal only as the last item of a `def' or a
     ;; word outright — unit is spelled `()'.  Drawing it as a valid type would
     ;; advertise a spelling the parser rejects, which is the same reason
     ;; `find-restart' and `await' are left out of `flan--special'.
-    ("\\_<\\(?:[iu]\\(?:8\\|16\\|32\\|64\\)\\|f\\(?:32\\|64\\)\\|bool\\|string\\|dyn\\|int\\|float\\|Never\\|Allocator\\|Ptr\\|Option\\|Vec\\|Map\\|Fn\\)\\_>"
+    ("\\_<\\(?:[iu]\\(?:8\\|16\\|32\\|64\\)\\|f\\(?:32\\|64\\)\\|bool\\|string\\|dyn\\|int\\|float\\|Never\\|Allocator\\|Ptr\\|Option\\|Vec\\|Map\\|C?Fn\\)\\_>"
      . font-lock-type-face)
     ;; A type variable, `$t', which is what a generic `defn' names its
     ;; parameter types with and what `{:where (ordered? $t)}' constrains.

emacs/flan.el

@@ -78,6 +78,15 @@
 ;; the commands here and requires nothing back.
 (require 'flan-mode)
 
+(defun flan--navigable-notes ()
+  "Make `next-error' stop on a note as well as on an error, in this buffer.
+A diagnostic's notes are `file:line:col: note: ...' lines, and `compile'
+reads the word `note' as an info message.  Its default
+`compilation-skip-threshold' of 1 steps over info messages, so the second
+location a diagnostic names was clickable but never reached by `next-error'.
+Zero skips nothing.  A note is not relabelled as a warning to get there."
+  (setq-local compilation-skip-threshold 0))
+
 (defgroup flan nil
   "Talking to a running Flan program."
   :group 'flan
@@ -821,7 +830,8 @@ It builds the program first, which for a cold project is most of this."
       ;; program runs, and `compilation-mode' would claim it as the output of
       ;; one finished command — killing the process on a `recompile', among
       ;; other things it has no business doing to a live session.
-      (compilation-minor-mode 1))
+      (compilation-minor-mode 1)
+      (flan--navigable-notes))
     (make-process
      :name "flan-daemon" :buffer buf
      :command args
@@ -1449,7 +1459,8 @@ no longer wrong."
   ;; should go there.  The minor mode rather than deriving from
   ;; `compilation-mode', because this buffer is not the output of a command
   ;; that ran once.
-  (compilation-minor-mode 1))
+  (compilation-minor-mode 1)
+  (flan--navigable-notes))
 
 (defvar-local flan--diagnostics-memory-start nil
   "Marker at the start of the memory section, or nil while there is none.

emacs/test-flan-cider.el

@@ -1680,6 +1680,31 @@ stopped program, which is the case where it should fire."
       (eq (key-binding (kbd k)) #'flan-macroexpand--not-source))
     '("C-c C-c" "C-c C-k" "C-x C-e"))))
 
+;; A diagnostic's note is a second `file:line:col:' line, labelled `note:'.
+;; `compile' reads it as an info message, and next-error has to stop on it as
+;; well as on the error above it, in both buffers that carry diagnostics.
+(message "\nnext-error reaches a note")
+(let ((flan-diagnostics-buffer " *test-flan-diag*"))
+  (with-current-buffer (get-buffer-create flan-diagnostics-buffer)
+    (flan-diagnostics-mode)
+    (let ((inhibit-read-only t))
+      (insert "a.flan:3:5: cannot add a bool to an i64\n"
+              "     ^\n"
+              "a.flan:1:7: note: the bool was bound here\n"
+              "     -\n"
+              "b.flan:9:2: the next error\n"))
+    (goto-char (point-min))
+    (compilation-next-error 1)
+    (test-flan--check "from the error, n lands on its note"
+                      (looking-at "a.flan:1:7: note:"))
+    (compilation-next-error 1)
+    (test-flan--check "and then on the next error"
+                      (looking-at "b.flan:9:2:"))
+    (test-flan--check "the threshold is this buffer's, not the user's setting"
+                      (and (local-variable-p 'compilation-skip-threshold)
+                           (eql (default-value 'compilation-skip-threshold) 1))))
+  (kill-buffer flan-diagnostics-buffer))
+
 ;; `flan-mode' itself — indentation, which is a function from text to text and
 ;; so belongs with the other fixture-driven checks rather than with anything
 ;; that needs a daemon.  Loaded rather than run separately because

emacs/test-flan-mode.el

@@ -425,6 +425,8 @@
                 ("(def v (Vec u8))" "Vec" font-lock-type-face "Vec")
                 ("(declare apply [(Fn [i64] i64)] i64)" "Fn"
                  font-lock-type-face "Fn")
+                ("(declare call [(CFn [i64] i64)] i64)" "CFn"
+                 font-lock-type-face "CFn")
                 ("(defn seen? [k $t] bool 1)" "$t" font-lock-type-face
                  "a type variable")
                 ;; The package alias of a qualified name, `clojure-mode''s