Update changelog and make arg to peg's error optional.

CHANGELOG.md

@@ -2,6 +2,12 @@
 All notable changes to this project will be documented in this file.
 
 ## Unreleased - ???
+- Backtick delimited strings and buffers are now reindented based on the column of the
+  opening delimiter. WHitespace in columns to the left of the starting column is ignored unless
+  there are non-space/non-newline characters in that region, in which case the old behavior is preserved.
+- Argument to `(error)` combinator in PEGs is now optional.
+- Add `(line)` and `(column)` combinators to PEGs to capture source line and column.
+  This should make error reporting a bit easier.
 - During installation and release, merge janetconf.h into janet.h for easier install.
 - Add `upscope` special form.
 - `os/execute` and `os/spawn` can take streams for redirecting IO.

src/core/peg.c

@@ -488,8 +488,9 @@ tail:
             } else {
                 /* Throw generic error */
                 int32_t start = (int32_t)(text - s->text_start);
+                LineCol lc = get_linecol_from_position(s, start);
                 int32_t end = (int32_t)(result - s->text_start);
-                janet_panicf("match error in range (%d:%d)", start, end);
+                janet_panicf("match error at line %d, column %d", lc.line, lc.col);
             }
             return NULL;
         }
@@ -898,7 +899,13 @@ static void spec_not(Builder *b, int32_t argc, const Janet *argv) {
     spec_onerule(b, argc, argv, RULE_NOT);
 }
 static void spec_error(Builder *b, int32_t argc, const Janet *argv) {
-    spec_onerule(b, argc, argv, RULE_ERROR);
+    if (argc == 0) {
+        Reserve r = reserve(b, 2);
+        uint32_t rule = peg_compile1(b, janet_wrap_number(0));
+        emit_1(r, RULE_ERROR, rule);
+    } else {
+        spec_onerule(b, argc, argv, RULE_ERROR);
+    }
 }
 static void spec_drop(Builder *b, int32_t argc, const Janet *argv) {
     spec_onerule(b, argc, argv, RULE_DROP);