Add line and column combinators to peg.

These capture the line and column number of the current position
in the matched text. This is useful for error reporting as well
as indentation checking.

This works by lazily creating an index on first use that stores all
newline character indices in order. We can then do a binary search on
this to get both line number and column number in log(n) time.
This is good enough for most use cases and doesn't slow down the common case at all
- these will not be commonly used patterns in a hot loop so it is not worth to try and
optimize this at all. Constant time look up should be possible but at
the cost of complicating code and slowing down all matching to check for
new lines.

src/core/peg.c

@@ -45,8 +45,10 @@ typedef struct {
     JanetBuffer *scratch;
     JanetBuffer *tags;
     const Janet *extrav;
+    int32_t *linemap;
     int32_t extrac;
     int32_t depth;
+    int32_t linemaplen;
     enum {
         PEG_MODE_NORMAL,
         PEG_MODE_ACCUMULATE
@@ -87,6 +89,60 @@ static void pushcap(PegState *s, Janet capture, uint32_t tag) {
     }
 }
 
+/* Lazily generate line map to get line and column information for PegState.
+ * line and column are 1-indexed. */
+typedef struct {
+    int32_t line;
+    int32_t col;
+} LineCol;
+static LineCol get_linecol_from_position(PegState *s, int32_t position) {
+    /* Generate if not made yet */
+    if (s->linemaplen < 0) {
+        int32_t newline_count = 0;
+        for (const uint8_t *c = s->text_start; c < s->text_end; c++) {
+            if (*c == '\n') newline_count++;
+        }
+        int32_t *mem = malloc(sizeof(int32_t) * newline_count);
+        if (NULL == mem) {
+            JANET_OUT_OF_MEMORY;
+        }
+        size_t index = 0;
+        for (const uint8_t *c = s->text_start; c < s->text_end; c++) {
+            if (*c == '\n') mem[index++] = (int32_t)(c - s->text_start);
+        }
+        s->linemaplen = newline_count;
+        s->linemap = mem;
+    }
+    /* Do binary search for line. Slightly modified from classic binary search:
+     * - if we find that our current character is a line break, just return immediately.
+     *   a newline character is consider to be on the same line as the character before
+     *   (\n is line terminator, not line separator).
+     * - in the not-found case, we still want to find the greatest-indexed newline that
+     *   is before position. we use that to calcuate the line and column.
+     * - in the case that lo = 0 and s->linemap[0] is still greater than position, we
+     *   are on the first line and our column is position + 1. */
+    int32_t hi = s->linemaplen; /* hi is greater than the actual line */
+    int32_t lo = 0; /* lo is less than or equal to the actual line */
+    LineCol ret;
+    while (lo + 1 < hi) {
+        int32_t mid = lo + (hi - lo) / 2;
+        if (s->linemap[mid] >= position) {
+            hi = mid;
+        } else {
+            lo = mid;
+        }
+    }
+    /* first line case */
+    if (s->linemaplen == 0 || (lo == 0 && s->linemap[0] >= position)) {
+        ret.line = 1;
+        ret.col = position + 1;
+    } else {
+        ret.line = lo + 2;
+        ret.col = position - s->linemap[lo];
+    }
+    return ret;
+}
+
 /* Convert a uint64_t to a int64_t by wrapping to a maximum number of bytes */
 static int64_t peg_convert_u64_s64(uint64_t from, int width) {
     int shift = 8 * (8 - width);
@@ -280,6 +336,18 @@ tail:
             return text;
         }
 
+        case RULE_LINE: {
+            LineCol lc = get_linecol_from_position(s, (int32_t) (text - s->text_start));
+            pushcap(s, janet_wrap_number((double)(lc.line)), rule[1]);
+            return text;
+        }
+
+        case RULE_COLUMN: {
+            LineCol lc = get_linecol_from_position(s, (int32_t) (text - s->text_start));
+            pushcap(s, janet_wrap_number((double)(lc.col)), rule[1]);
+            return text;
+        }
+
         case RULE_ARGUMENT: {
             int32_t index = ((int32_t *)rule)[1];
             Janet capture = (index >= s->extrac) ? janet_wrap_nil() : s->extrav[index];
@@ -880,6 +948,12 @@ static void spec_tag1(Builder *b, int32_t argc, const Janet *argv, uint32_t op)
 static void spec_position(Builder *b, int32_t argc, const Janet *argv) {
     spec_tag1(b, argc, argv, RULE_POSITION);
 }
+static void spec_line(Builder *b, int32_t argc, const Janet *argv) {
+    spec_tag1(b, argc, argv, RULE_LINE);
+}
+static void spec_column(Builder *b, int32_t argc, const Janet *argv) {
+    spec_tag1(b, argc, argv, RULE_COLUMN);
+}
 
 static void spec_backmatch(Builder *b, int32_t argc, const Janet *argv) {
     spec_tag1(b, argc, argv, RULE_BACKMATCH);
@@ -983,6 +1057,7 @@ static const SpecialPair peg_specials[] = {
     {"capture", spec_capture},
     {"choice", spec_choice},
     {"cmt", spec_matchtime},
+    {"column", spec_column},
     {"constant", spec_constant},
     {"drop", spec_drop},
     {"error", spec_error},
@@ -992,6 +1067,7 @@ static const SpecialPair peg_specials[] = {
     {"int", spec_int_le},
     {"int-be", spec_int_be},
     {"lenprefix", spec_lenprefix},
+    {"line", spec_line},
     {"look", spec_look},
     {"not", spec_not},
     {"opt", spec_opt},
@@ -1229,6 +1305,8 @@ static void *peg_unmarshal(JanetMarshalContext *ctx) {
             case RULE_NOTNCHAR:
             case RULE_RANGE:
             case RULE_POSITION:
+            case RULE_LINE:
+            case RULE_COLUMN:
             case RULE_BACKMATCH:
                 /* [1 word] */
                 i += 2;
@@ -1438,6 +1516,8 @@ static PegCall peg_cfun_init(int32_t argc, Janet *argv, int get_replace) {
     ret.s.tags = janet_buffer(10);
     ret.s.constants = ret.peg->constants;
     ret.s.bytecode = ret.peg->bytecode;
+    ret.s.linemap = NULL;
+    ret.s.linemaplen = -1;
     return ret;
 }
 

src/include/janet.h

@@ -1784,7 +1784,9 @@ typedef enum {
     RULE_THRU,         /* [rule] */
     RULE_LENPREFIX,    /* [rule_a, rule_b (repeat rule_b rule_a times)] */
     RULE_READINT,      /* [(signedness << 4) | (endianess << 5) | bytewidth, tag] */
-} JanetPegOpcode;
+    RULE_LINE,         /* [tag] */
+    RULE_COLUMN        /* [tag] */
+} JanetPegOpcod;
 
 typedef struct {
     uint32_t *bytecode;

test/suite0003.janet

@@ -360,6 +360,14 @@
 (check-match janet-longstring "``` `` ```" true)
 (check-match janet-longstring "``  ```" false)
 
+# Line and column capture
+
+(def line-col (peg/compile '(any (* (line) (column) 1))))
+(check-deep line-col "abcd" @[1 1 1 2 1 3 1 4])
+(check-deep line-col "" @[])
+(check-deep line-col "abcd\n" @[1 1 1 2 1 3 1 4 1 5])
+(check-deep line-col "abcd\nz" @[1 1 1 2 1 3 1 4 1 5 2 1])
+
 # Backmatch
 
 (def backmatcher-1 '(* (capture (any "x") :1) "y" (backmatch :1) -1))