Expose line, col in macros via (dyn :macro-form)

This exposes line and column indirectly via
tuple/sourcemap and allows interesting debug macros.

CHANGELOG.md

@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Expose current macro form inside macros as (dyn :macro-form)
 - Add `tracev` macro.
 - Fix compiler bug that emitted incorrect code in some cases for while loops that create closures.
 - Add `:fresh` option to `(import ...)` to overwrite the module cache.

src/boot/boot.janet

@@ -950,9 +950,14 @@
   "Print a value and a description of the form that produced that value to
   stderr. Evaluates to x."
   [x]
+  (def [l c] (tuple/sourcemap (dyn :macro-form ())))
+  (def cf (dyn :current-file))
+  (def fmt-1 (if cf (string/format "trace [%s]" cf) "trace"))
+  (def fmt-2 (if (or (neg? l) (neg? c)) ": " (string/format " on line %d, column %d:" l c)))
+  (def fmt (string fmt-1 fmt-2 " %j is "))
   (def s (gensym))
   ~(let [,s ,x]
-     (,eprinf "trace %j is " ',x)
+     (,eprinf ,fmt ',x)
      (,eprintf (,dyn :pretty-format "%q") ,s)
      ,s))
 
@@ -1628,6 +1633,8 @@
   See macex docs for info on on-binding."
   [x &opt on-binding]
 
+  (setdyn :macro-form x)
+
   (when on-binding
     (when (symbol? x)
       (break (on-binding x))))

src/core/compile.c

@@ -596,8 +596,11 @@ static int macroexpand1(
     /* Set env */
     fiberp->env = c->env;
     int lock = janet_gclock();
+    Janet mf_kw = janet_ckeywordv("macro-form");
+    janet_table_put(c->env, mf_kw, x);
     Janet tempOut;
     JanetSignal status = janet_continue(fiberp, janet_wrap_nil(), &tempOut);
+    janet_table_put(c->env, mf_kw, janet_wrap_nil());
     janet_gcunlock(lock);
     if (status != JANET_SIGNAL_OK) {
         const uint8_t *es = janet_formatc("(macro) %V", tempOut);