sl0ppty: render the config instead of shipping a copy of it

`C-a e` on a machine with no config opened an empty buffer, which tells you
nothing about what you can set. The obvious fix -- embed config/config.kdl and
write it out -- trades one problem for a worse one: a checked-in copy of the
defaults is a second source of truth, and it drifts. Ours already had. Four
theme colours existed in the code and not in that file, and nothing said so.

So the file is generated. `sl0ppty --dump-config` renders every setting with
the value it currently holds -- geometry, behaviour, all 48 theme colours, the
state shader chains, and every binding including the leader-less ones -- and
`C-a e` seeds a missing config with exactly that, creating the directories on
the way (a fresh container has no ~/.config either).

config/config.kdl stays, and is now explicitly the *prose*: what a setting is
for, what it cost to get right, which ones are opinions. Values are generated,
essays are written, and the file says so at the top.

Three things keep the two honest:

- the theme colours became one file-scope table that the parser and the
  renderer both walk. 48 names that used to exist in one place and be typed
  again in another now exist once.
- the dump must parse back to itself byte-for-byte. That is what caught
  `bind \ split-cols` rendering unquoted -- valid-looking output that would
  not have survived being read back.
- a test scans config.c for `kdl_child(root, "...")`, which is the parser's
  own vocabulary, and fails if a key is missing from the dump. Add a knob,
  forget to render it, and the suite tells you rather than a user.

It never overwrites a config that exists: fopen(..., "wx") loses the race
rather than an edit, and there is a test for that too, because it is the one
thing here that must never go wrong.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/main.c b/src/main.c
index e2d0602..53689ee 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,6 +20,7 @@
 
 #include "proto.h"
 #include "server.h"
+#include "config.h"
 #include "version.h"
 
 int run_headless(const char *const argv[], uint16_t cols, uint16_t rows,
@@ -38,7 +39,8 @@ static void term_size(uint16_t *cols, uint16_t *rows) {
 
 static void usage(void) {
   fputs("usage: sl0ppty [-s NAME] [--layout FILE] [--no-reload]\n"
-        "                [--version] [ls | cmd LINE | -- CMD...]\n",
+        "                [--version] [--dump-config]\n"
+        "                [ls | cmd LINE | -- CMD...]\n",
         stderr);
 }
 
@@ -62,6 +64,15 @@ int main(int argc, char **argv) {
     else if (strcmp(a, "-s") == 0 && i + 1 < argc) name = argv[++i];
     else if (strcmp(a, "--layout") == 0 && i + 1 < argc) layout = argv[++i];
     else if (strcmp(a, "--no-reload") == 0) watch = false;
+    else if (strcmp(a, "--dump-config") == 0) {
+      /* Every setting with the value it currently has, as a file you could
+       * have written. `sl0ppty --dump-config > ~/.config/sl0ppty/config.kdl`
+       * is a supported way to start one. */
+      char *text = config_dump_defaults();
+      fputs(text, stdout);
+      free(text);
+      return 0;
+    }
     else if (strcmp(a, "--version") == 0) {
       /* The same string the status line shows, so "which build is this" has
        * one answer whether you ask the binary or the session. */