term: add capability to print warnings *inside* the terminal

This is intended to be used to print e.g. deprecation warnings inside
the terminal, *before* the shell is started.

config.c

@@ -1170,6 +1170,8 @@ config_load(struct config *conf, const char *conf_path)
             .delayed_render_upper_ns = 16666666 / 2,   /* half a frame period (60Hz) */
             .max_shm_pool_size = 512 * 1024 * 1024,
         },
+
+        .warnings = tll_init(),
     };
 
     struct config_key_binding_normal scrollback_up =   {BIND_ACTION_SCROLLBACK_UP,   strdup("Shift+Page_Up")};
@@ -1284,6 +1286,10 @@ config_free(struct config conf)
     tll_free(conf.bindings.key);
     tll_free(conf.bindings.mouse);
     tll_free(conf.bindings.search);
+
+    tll_foreach(conf.warnings, it)
+        free(it->item.text);
+    tll_free(conf.warnings);
 }
 
 struct config_font

config.h

@@ -119,6 +119,8 @@ struct config {
         uint64_t delayed_render_upper_ns;
         off_t max_shm_pool_size;
     } tweak;
+
+    user_warning_list_t warnings;
 };
 
 bool config_load(struct config *conf, const char *path);

slave.c

@@ -18,6 +18,7 @@
 #define LOG_ENABLE_DBG 0
 #include "log.h"
 
+#include "terminal.h"
 #include "tokenize.h"
 
 static bool
@@ -67,7 +68,8 @@ err:
 }
 
 static void
-slave_exec(int ptmx, char *argv[], int err_fd, bool login_shell)
+slave_exec(int ptmx, char *argv[], int err_fd, bool login_shell,
+           size_t warning_count, struct user_warning warnings[static warning_count])
 {
     int pts = -1;
     const char *pts_name = ptsname(ptmx);
@@ -122,6 +124,18 @@ slave_exec(int ptmx, char *argv[], int err_fd, bool login_shell)
         goto err;
     }
 
+    for (size_t i = 0; i < warning_count; i++) {
+        switch (warnings[i].kind) {
+        case USER_WARNING_DEPRECATION:
+            write(pts, "\e[33;1;5mdeprecated:\e[39;21;25m ", 32);
+        }
+
+        write(pts, warnings[i].text, strlen(warnings[i].text));
+        write(pts, "\e[m\n", 4);
+        free(warnings[i].text);
+    }
+    free(warnings);
+
     close(pts);
     pts = -1;
 
@@ -152,7 +166,8 @@ err:
 
 pid_t
 slave_spawn(int ptmx, int argc, const char *cwd, char *const *argv,
-            const char *term_env, const char *conf_shell, bool login_shell)
+            const char *term_env, const char *conf_shell, bool login_shell,
+            const user_warning_list_t *warnings)
 {
     int fork_pipe[2];
     if (pipe2(fork_pipe, O_CLOEXEC) < 0) {
@@ -220,7 +235,20 @@ slave_spawn(int ptmx, int argc, const char *cwd, char *const *argv,
         if (is_valid_shell(shell_argv[0]))
             setenv("SHELL", shell_argv[0], 1);
 
-        slave_exec(ptmx, shell_argv, fork_pipe[1], login_shell);
+        struct user_warning *warnings_copy = malloc(
+            tll_length(*warnings) * sizeof(warnings_copy[0]));
+        {
+            size_t i = 0;
+            tll_foreach(*warnings, it){
+                warnings_copy[i] = (struct user_warning){
+                    .kind = it->item.kind,
+                    .text = strdup(it->item.text),
+                };
+            }
+        }
+
+        slave_exec(ptmx, shell_argv, fork_pipe[1], login_shell,
+                   tll_length(*warnings), warnings_copy);
         assert(false);
         break;
 

slave.h

@@ -3,6 +3,9 @@
 
 #include <sys/types.h>
 
+#include "terminal.h"
+
 pid_t slave_spawn(
     int ptmx, int argc, const char *cwd, char *const *argv, const char *term_env,
-    const char *conf_shell, bool login_shell);
+    const char *conf_shell, bool login_shell,
+    const user_warning_list_t *warnings);

terminal.c

@@ -943,7 +943,8 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
     /* Start the slave/client */
     if ((term->slave = slave_spawn(
              term->ptmx, argc, term->cwd, argv,
-             conf->term, conf->shell, conf->login_shell)) == -1)
+             conf->term, conf->shell, conf->login_shell,
+             &conf->warnings)) == -1)
     {
         goto err;
     }

terminal.h

@@ -206,6 +206,12 @@ enum term_surface {
     TERM_SURF_BUTTON_CLOSE,
 };
 
+struct user_warning {
+    enum { USER_WARNING_DEPRECATION } kind;
+    char *text;
+};
+typedef tll(struct user_warning) user_warning_list_t;
+
 struct terminal {
     struct fdm *fdm;
     struct reaper *reaper;