parse: add the gap shorthand

src/parse/properties/Makefile

@@ -51,6 +51,7 @@ DIR_SOURCES :=				\
 	font.c				\
 	font_family.c			\
 	font_weight.c			\
+	gap.c				\
 	list_style.c			\
 	list_style_type.c		\
 	margin.c			\

src/parse/properties/gap.c

@@ -0,0 +1,164 @@
+/*
+ * This file is part of LibCSS.
+ * Licensed under the MIT License,
+ *		  http://www.opensource.org/licenses/mit-license.php
+ * Copyright 2026 Cyril Hrubis <metan@ucw.cz>
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include "bytecode/bytecode.h"
+#include "bytecode/opcodes.h"
+#include "parse/properties/properties.h"
+#include "parse/properties/utils.h"
+
+/**
+ * Parse a single gap component: normal | <length>
+ *
+ * \param c	  Parsing context
+ * \param vector  Vector of tokens to process
+ * \param ctx	  Pointer to vector iteration context
+ * \param normal  Pointer to location to receive "is normal" flag
+ * \param length  Pointer to location to receive the length
+ * \param unit	  Pointer to location to receive the length's unit
+ * \return CSS_OK on success, CSS_INVALID if the input is not a gap component
+ *
+ * Post condition: \a *ctx is updated with the next token to process
+ *		   If the input is invalid, then \a *ctx remains unchanged.
+ */
+static css_error parse_gap_component(css_language *c,
+		const parserutils_vector *vector, int32_t *ctx,
+		bool *normal, css_fixed *length, uint32_t *unit)
+{
+	int32_t orig_ctx = *ctx;
+	const css_token *token;
+	css_error error;
+	bool match;
+
+	token = parserutils_vector_peek(vector, *ctx);
+	if (token == NULL)
+		return CSS_INVALID;
+
+	if ((token->type == CSS_TOKEN_IDENT) &&
+			(lwc_string_caseless_isequal(token->idata,
+			c->strings[NORMAL], &match) == lwc_error_ok &&
+			match)) {
+		parserutils_vector_iterate(vector, ctx);
+		*normal = true;
+		return CSS_OK;
+	}
+
+	error = css__parse_unit_specifier(c, vector, ctx, UNIT_PX, length, unit);
+	if (error != CSS_OK) {
+		*ctx = orig_ctx;
+		return error;
+	}
+
+	if (*length < 0 || (*unit & UNIT_MASK_COLUMN_GAP) == 0) {
+		*ctx = orig_ctx;
+		return CSS_INVALID;
+	}
+
+	*normal = false;
+
+	return CSS_OK;
+}
+
+/**
+ * Parse gap shorthand
+ *
+ * gap: <row-gap> <column-gap>?  — one value sets both axes.
+ *
+ * LibCSS has no row-gap property (column-gap comes from multicol), so only
+ * the column component reaches the cascade.  The row component is still
+ * parsed and consumed, or the whole declaration would be rejected as
+ * invalid and the column gap lost with it.
+ *
+ * \param c	  Parsing context
+ * \param vector  Vector of tokens to process
+ * \param ctx	  Pointer to vector iteration context
+ * \param result  Pointer to location to receive resulting style
+ * \return CSS_OK on success,
+ *	   CSS_NOMEM on memory exhaustion,
+ *	   CSS_INVALID if the input is not valid
+ *
+ * Post condition: \a *ctx is updated with the next token to process
+ *		   If the input is invalid, then \a *ctx remains unchanged.
+ */
+css_error css__parse_gap(css_language *c,
+		const parserutils_vector *vector, int32_t *ctx,
+		css_style *result)
+{
+	int32_t orig_ctx = *ctx;
+	css_error error;
+	const css_token *token;
+	enum flag_value flag_value;
+	css_fixed length = 0;
+	uint32_t unit = 0;
+	bool normal = false;
+
+	token = parserutils_vector_peek(vector, *ctx);
+	if (token == NULL) {
+		return CSS_INVALID;
+	}
+
+	flag_value = get_css_flag_value(c, token);
+
+	if (flag_value != FLAG_VALUE__NONE) {
+		parserutils_vector_iterate(vector, ctx);
+
+		error = css_stylesheet_style_flag_value(result, flag_value,
+				CSS_PROP_COLUMN_GAP);
+		if (error != CSS_OK)
+			*ctx = orig_ctx;
+
+		return error;
+	}
+
+	/* Row component — parsed only to consume it. */
+	error = parse_gap_component(c, vector, ctx, &normal, &length, &unit);
+	if (error != CSS_OK) {
+		*ctx = orig_ctx;
+		return error;
+	}
+
+	consumeWhitespace(vector, ctx);
+
+	/* Column component, if any — it overrides the row one. */
+	token = parserutils_vector_peek(vector, *ctx);
+	if (token != NULL) {
+		css_fixed col_length = 0;
+		uint32_t col_unit = 0;
+		bool col_normal = false;
+
+		if (parse_gap_component(c, vector, ctx, &col_normal,
+				&col_length, &col_unit) == CSS_OK) {
+			length = col_length;
+			unit = col_unit;
+			normal = col_normal;
+		}
+	}
+
+	if (normal) {
+		error = css__stylesheet_style_appendOPV(result,
+				CSS_PROP_COLUMN_GAP, 0, COLUMN_GAP_NORMAL);
+		if (error != CSS_OK)
+			*ctx = orig_ctx;
+
+		return error;
+	}
+
+	error = css__stylesheet_style_appendOPV(result, CSS_PROP_COLUMN_GAP,
+			0, COLUMN_GAP_SET);
+	if (error != CSS_OK) {
+		*ctx = orig_ctx;
+		return error;
+	}
+
+	error = css__stylesheet_style_vappend(result, 2, length, unit);
+	if (error != CSS_OK)
+		*ctx = orig_ctx;
+
+	return error;
+}

src/parse/properties/properties.c

@@ -89,6 +89,7 @@ const css_prop_handler property_handlers[LAST_PROP + 1 - FIRST_PROP] =
 	css__parse_font_style,
 	css__parse_font_variant,
 	css__parse_font_weight,
+	css__parse_gap,
 	css__parse_height,
 	css__parse_justify_content,
 	css__parse_left,

src/parse/properties/properties.h

@@ -253,6 +253,9 @@ css_error css__parse_font_variant(css_language *c,
 css_error css__parse_font_weight(css_language *c,
 		const parserutils_vector *vector, int32_t *ctx,
 		css_style *result);
+css_error css__parse_gap(css_language *c,
+		const parserutils_vector *vector, int32_t *ctx,
+		css_style *result);
 css_error css__parse_height(css_language *c,
 		const parserutils_vector *vector, int32_t *ctx,
 		css_style *result);

src/parse/propstrings.c

@@ -163,6 +163,7 @@ const stringmap_entry stringmap[LAST_KNOWN] = {
 	SMAP("font-style"),
 	SMAP("font-variant"),
 	SMAP("font-weight"),
+	SMAP("gap"),
 	SMAP("height"),
 	SMAP("justify-content"),
 	SMAP("left"),

src/parse/propstrings.h

@@ -54,7 +54,7 @@ enum {
 	CURSOR, DIRECTION, DISPLAY, ELEVATION, EMPTY_CELLS, FILL_OPACITY, FLEX,
 	FLEX_BASIS, FLEX_DIRECTION, FLEX_FLOW, FLEX_GROW, FLEX_SHRINK,
 	FLEX_WRAP, LIBCSS_FLOAT, FONT, FONT_FAMILY, FONT_SIZE, FONT_STYLE,
-	FONT_VARIANT, FONT_WEIGHT, HEIGHT, JUSTIFY_CONTENT, LEFT,
+	FONT_VARIANT, FONT_WEIGHT, GAP, HEIGHT, JUSTIFY_CONTENT, LEFT,
 	LETTER_SPACING, LINE_HEIGHT, LIST_STYLE, LIST_STYLE_IMAGE,
 	LIST_STYLE_POSITION, LIST_STYLE_TYPE, MARGIN, MARGIN_BOTTOM,
 	MARGIN_LEFT, MARGIN_RIGHT, MARGIN_TOP, MAX_HEIGHT, MAX_WIDTH,

test/data/parse2/multicol.dat

@@ -1301,3 +1301,108 @@
 #reset
 
 
+#data
+* { gap: 2em; }
+#errors
+#expected
+| *
+|  column-gap: 2em
+#reset
+
+#data
+* { gap: 1em 2em; }
+#errors
+#expected
+| *
+|  column-gap: 2em
+#reset
+
+#data
+* { gap: normal; }
+#errors
+#expected
+| *
+|  column-gap: normal
+#reset
+
+#data
+* { gap: normal 2em; }
+#errors
+#expected
+| *
+|  column-gap: 2em
+#reset
+
+#data
+* { gap: 1em normal; }
+#errors
+#expected
+| *
+|  column-gap: normal
+#reset
+
+#data
+* { gap: 0; }
+#errors
+#expected
+| *
+|  column-gap: 0px
+#reset
+
+#data
+* { gap: 1em 2em 3em; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: -1em; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: 2; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: 10%; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: auto; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: ; }
+#errors
+#expected
+| *
+#reset
+
+#data
+* { gap: inherit; }
+#errors
+#expected
+| *
+|  column-gap: inherit
+#reset
+
+#data
+* { gap: inherit !important; }
+#errors
+#expected
+| *
+|  column-gap: inherit !important
+#reset