syntax and diff background highlighting

Makefile

@@ -366,6 +366,7 @@ TIG_OBJS = \
 	src/grep.o \
 	src/ui.o \
 	src/apps.o \
+	src/ansi.o \
 	$(GRAPH_OBJS) \
 	$(COMPAT_OBJS)
 
@@ -374,10 +375,13 @@ src/tig: $(TIG_OBJS)
 TEST_GRAPH_OBJS = test/tools/test-graph.o src/string.o src/util.o src/io.o $(GRAPH_OBJS) $(COMPAT_OBJS)
 test/tools/test-graph: $(TEST_GRAPH_OBJS)
 
+TEST_ANSI_OBJS = test/tools/test-ansi.o src/ansi.o $(COMPAT_OBJS)
+test/tools/test-ansi: $(TEST_ANSI_OBJS)
+
 DOC_GEN_OBJS = tools/doc-gen.o src/string.o src/types.o src/util.o src/request.o $(COMPAT_OBJS)
 tools/doc-gen: $(DOC_GEN_OBJS)
 
-OBJS = $(sort $(TIG_OBJS) $(TEST_GRAPH_OBJS) $(DOC_GEN_OBJS))
+OBJS = $(sort $(TIG_OBJS) $(TEST_GRAPH_OBJS) $(TEST_ANSI_OBJS) $(DOC_GEN_OBJS))
 
 DEPS_CFLAGS ?= -MMD -MP -MF .deps/$*.d
 

doc/tigrc.5.adoc

@@ -291,6 +291,23 @@ The following variables can be set:
 	regions are governed by `color diff-add-highlight` and
 	`color diff-del-highlight`.
 
+'syntax-highlight' (mixed)::
+
+	Whether to syntax-highlight file contents in diff, stage, blob, and
+	pager views using an external highlighter. Defaults to false. When set
+	to true then 'bat' is used, else the option value is used as the path
+	to the highlighter command. Requires a terminal with 256-color support
+	(TERM=xterm-256color or equivalent); silently disabled on terminals
+	with fewer than 256 colors. +
+	 +
+	When enabled, diff views show syntax-colored code on dark green
+	(additions) or dark red (deletions) backgrounds. Can be combined with
+	'diff-highlight' for intra-line change emphasis. Long lines are wrapped
+	with a 2-space indent on continuation lines. +
+	 +
+	The highlighter must accept `--color=always --style=plain --paging=never
+	--file-name=<name> -` arguments and read from stdin.
+
 'diff-indicator' (bool)::
 
 	Show +/- signs in the diff view. On by default.

include/tig/ansi.h

@@ -0,0 +1,65 @@
+/* Copyright (c) 2006-2026 Jonas Fonseca <jonas.fonseca@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef TIG_ANSI_H
+#define TIG_ANSI_H
+
+#include "tig/tig.h"
+
+#define ANSI_MAX_SPANS	512
+
+enum ansi_color_type {
+	ANSI_COLOR_DEFAULT,
+	ANSI_COLOR_BASIC,	/* 0-7: standard ANSI colors */
+	ANSI_COLOR_256,		/* 0-255: extended palette */
+	ANSI_COLOR_RGB		/* 24-bit truecolor */
+};
+
+struct ansi_color {
+	enum ansi_color_type type;
+	union {
+		int index;
+		struct { unsigned char r, g, b; } rgb;
+	};
+};
+
+struct ansi_span {
+	struct ansi_color fg;
+	struct ansi_color bg;
+	int attr;		/* ncurses attributes: A_BOLD, A_UNDERLINE, etc. */
+	size_t offset;		/* byte offset in stripped text */
+	size_t length;		/* byte length of this span */
+};
+
+/*
+ * Parse a line containing ANSI escape sequences.
+ *
+ * Strips escape codes from `raw` and writes plain text to `stripped`.
+ * Records color/attribute spans in `spans`.
+ *
+ * Returns the number of spans written, or -1 on error.
+ */
+int ansi_parse_line(const char *raw, char *stripped, size_t stripped_size,
+		    struct ansi_span *spans, int max_spans);
+
+/*
+ * Returns true if the string contains ANSI escape sequences.
+ */
+static inline bool
+ansi_has_escapes(const char *text)
+{
+	return text && strchr(text, 0x1b) != NULL;
+}
+
+#endif
+/* vim: set ts=8 sw=8 noexpandtab: */

include/tig/apps.h

@@ -33,6 +33,12 @@ struct app_external {
 
 struct app_external *app_diff_highlight_load(const char *query);
 
+/*
+ * syntax-highlight (bat)
+ */
+
+struct app_external *app_syntax_highlight_load(const char *query, const char *filename);
+
 #endif
 
 /* vim: set ts=8 sw=8 noexpandtab: */

include/tig/diff.h

@@ -30,6 +30,12 @@ struct diff_state {
 	unsigned int lineno;
 	struct position pos;
 	struct io view_io;
+	/* Syntax highlighting state */
+	bool syntax_highlight;
+	char syntax_file[SIZEOF_STR];	/* Current file from diff +++ header */
+	pid_t syntax_pid;		/* Persistent bat process */
+	int syntax_write_fd;		/* Write content to bat stdin */
+	FILE *syntax_read_fp;		/* Read highlighted output from bat stdout */
 };
 
 enum request diff_common_edit(struct view *view, enum request request, struct line *line);
@@ -41,6 +47,8 @@ void diff_save_line(struct view *view, struct diff_state *state, enum open_flags
 void diff_restore_line(struct view *view, struct diff_state *state);
 enum status_code diff_init_highlight(struct view *view, struct diff_state *state);
 bool diff_done_highlight(struct diff_state *state);
+void diff_init_syntax_highlight(struct diff_state *state);
+void diff_done_syntax_highlight(struct diff_state *state);
 
 unsigned int diff_get_lineno(struct view *view, struct line *line, bool old);
 const char *diff_get_pathname(struct view *view, struct line *line, bool old);

include/tig/line.h

@@ -154,5 +154,12 @@ get_line_attr(const char *prefix, enum line_type type)
 	return COLOR_PAIR(COLOR_ID(info->color_pair)) | info->attr;
 }
 
+/*
+ * Dynamic color pair allocation for syntax highlighting.
+ */
+struct ansi_color;
+int ansi_color_to_ncurses(const struct ansi_color *color);
+int get_dynamic_color_pair(const struct ansi_color *fg, const struct ansi_color *bg);
+
 #endif
 /* vim: set ts=8 sw=8 noexpandtab: */

include/tig/options.h

@@ -84,6 +84,7 @@ typedef struct view_column *view_settings;
 	_(status_show_untracked_dirs,	bool,			VIEW_STATUS_LIKE) \
 	_(status_show_untracked_files,	bool,			VIEW_STATUS_LIKE) \
 	_(status_view,			view_settings,		VIEW_NO_FLAGS) \
+	_(syntax_highlight,		const char *,		VIEW_NO_FLAGS) \
 	_(tab_size,			int,			VIEW_NO_FLAGS) \
 	_(tree_view,			view_settings,		VIEW_NO_FLAGS) \
 	_(truncation_delimiter,		const char *,		VIEW_NO_FLAGS) \

include/tig/view.h

@@ -28,6 +28,9 @@ struct view_ops;
 struct box_cell {
 	enum line_type type;
 	size_t length;
+	unsigned int direct : 1;	/* If set, use color_pair/attr directly */
+	int color_pair;			/* Dynamic ncurses color pair ID */
+	int attr;			/* A_BOLD | A_UNDERLINE | ... */
 };
 
 struct box {