Add command completion with tab key

In the command prompt, press <tab> to get a list of all available
commands and pick one (using vis-menu). This works also after typing the
first letters of a command (p.e. `:la<tab>`).

Co-authored-by: Matěj Cepl <mcepl@cepl.eu>

4 files changed, 67 insertions, 4 deletions

diff --git a/lua/plugins/complete-filename.lua b/lua/plugins/complete-filename.lua
index 604361c..db0f2a7 100644
--- a/lua/plugins/complete-filename.lua
+++ b/lua/plugins/complete-filename.lua
@@ -29,9 +29,19 @@ local complete_filename = function(expand)
 		prefix = home .. prefix:sub(j + 1)
 	end
 
-	local cmdfmt = "vis-complete --file '%s'"
-	if expand then cmdfmt = "vis-open -- '%s'*" end
-	local status, out, err = vis:pipe(cmdfmt:format(prefix:gsub("'", "'\\''")))
+	local status, out, err
+	if prefix:sub(1, 1) == ":" then
+		status, out, err = vis:complete_command(prefix:sub(2))
+		if out then
+			out = out:gsub("\n$", ""):sub(#prefix) .. " "
+		end
+		pos = range.start + #prefix
+		expand = false
+	else
+		local cmdfmt = "vis-complete --file '%s'"
+		if expand then cmdfmt = "vis-open -- '%s'*" end
+		status, out, err = vis:pipe(cmdfmt:format(prefix:gsub("'", "'\\''")))
+	end
 	if status ~= 0 or not out then
 		if err then vis:info(err) end
 		return
@@ -55,4 +65,4 @@ end, "Complete file name")
 -- complete file path at primary selection location using vis-open(1)
 vis:map(vis.modes.INSERT, "<C-x><C-o>", function()
 	complete_filename(true);
-end, "Complete file name (expands path)")
+end, "Complete file name (expands path) or command")
diff --git a/vis-cmds.c b/vis-cmds.c
index 482508f..b543683 100644
--- a/vis-cmds.c
+++ b/vis-cmds.c
@@ -693,6 +693,15 @@ static bool print_cmd(const char *key, void *value, void *data) {
 	return text_appendf(data, "  %-30s %s\n", usage, help ? help : "");
 }
 
+static bool print_cmd_name(const char *key, void *value, void *data) {
+	CommandDef *cmd = value;
+	return buffer_appendf(data, "%s\n", cmd->name);
+}
+
+void vis_print_cmds(Vis *vis, Buffer *buf) {
+	map_iterate(vis->cmds, print_cmd_name, buf);
+}
+
 static bool print_option(const char *key, void *value, void *txt) {
 	char desc[256];
 	const OptionDef *opt = value;
diff --git a/vis-lua.c b/vis-lua.c
index 695ebdb..99d9746 100644
--- a/vis-lua.c
+++ b/vis-lua.c
@@ -1147,6 +1147,41 @@ static int command_register(lua_State *L) {
 }
 
 /***
+ * Let user pick a command matching the given prefix.
+ *
+ * The editor core will be blocked while the external process is running.
+ *
+ * @function complete_command
+ * @tparam string prefix the prefix of the command to be completed
+ * @treturn int code the exit status of the executed command
+ * @treturn string stdout the data written to stdout
+ * @treturn string stderr the data written to stderr
+ */
+static int complete_command(lua_State *L) {
+	Vis *vis = obj_ref_check(L, 1, "vis");
+	const char *prefix = luaL_checkstring(L, 2);
+	char *out = NULL, *err = NULL;
+	char cmd[32];
+	int max_prefix_len = sizeof(cmd) - sizeof("grep '^' | vis-menu -b"); // including NUL
+	snprintf(cmd, sizeof(cmd), "grep '^%.*s' | vis-menu -b", max_prefix_len, prefix);
+
+	Buffer buf = {0};
+	vis_print_cmds(vis, &buf);
+	int status = vis_pipe_buf_collect(vis, buffer_content0(&buf), (const char*[]){cmd, NULL}, &out, &err, false);
+
+	lua_pushinteger(L, status);
+	if (out) lua_pushstring(L, out);
+	else     lua_pushnil(L);
+	if (err) lua_pushstring(L, err);
+	else     lua_pushnil(L);
+
+	free(out);
+	free(err);
+	buffer_release(&buf);
+	return 3;
+}
+
+/***
  * Push keys to input queue and interpret them.
  *
  * The keys are processed as if they were read from the keyboard.
@@ -1559,6 +1594,7 @@ static const struct luaL_Reg vis_lua[] = {
 	{ "option_register", option_register },
 	{ "option_unregister", option_unregister },
 	{ "command_register", command_register },
+	{ "complete_command", complete_command },
 	{ "feedkeys", feedkeys },
 	{ "insert", insert },
 	{ "replace", replace },
diff --git a/vis.h b/vis.h
index 2e66b77..01bf1a0 100644
--- a/vis.h
+++ b/vis.h
@@ -14,6 +14,7 @@ typedef struct Win Win;
 #include "text-regex.h"
 #include "libutf.h"
 #include "array.h"
+#include "buffer.h"
 
 #ifndef CONFIG_HELP
 #define CONFIG_HELP 1
@@ -1230,6 +1231,13 @@ bool vis_option_unregister(Vis *vis, const char *name);
 bool vis_prompt_cmd(Vis *vis, const char *cmd);
 
 /**
+ * Write newline separated list of available commands to ``buf``
+ * @param vis The editor instance.
+ * @param buf The buffer to write to.
+ */
+void vis_print_cmds(Vis*, Buffer *buf);
+
+/**
  * Pipe a given file range to an external process.
  * @param vis The editor instance.
  * @param file The file to pipe.