pty: install the terminfo entry implicitly when it is missing everywhere

The lookup miss now writes the embedded entry to ~/.terminfo and
uses it, so a bare box gets the full TERM with no step at all. An
entry that exists anywhere is respected -- possibly newer, certainly
somebody's -- and a HOME that cannot be written leaves the
xterm-256color fallback standing. --install-terminfo stays as the
by-hand spelling; the writer moved to pty.c where the panes are.

4 files changed, 71 insertions, 62 deletions

diff --git a/docs/slosh.1 b/docs/slosh.1
index cce0b64..6436f6a 100644
--- a/docs/slosh.1
+++ b/docs/slosh.1
@@ -152,12 +152,9 @@ Write the
 .B xterm-ghostty
 terminfo entry the binary carries into
 .I ~/.terminfo
-(no root, no package), so panes on a machine without ghostty's entry
-get the full
-.B TERM
-instead of the
-.B xterm-256color
-fallback.
+(no root, no package).
+Sessions do this on their own when the entry is missing everywhere; the
+flag is the by-hand spelling, for provisioning and for saying so.
 See ENVIRONMENT.
 .TP
 .BI \-\-server\  name
@@ -364,14 +361,16 @@ Set in every pane:
 .TP
 .B TERM
 .B xterm-ghostty
-when the machine's terminfo database has the entry (it ships with ghostty),
-.B xterm-256color
-when it does not: an entry curses cannot find makes editors exit on
-the spot and backspace guess.
-.B slosh \-\-install\-terminfo
-puts the real entry in
-.IR ~/.terminfo ;
-new sessions then use it.
+\(en found in the machine's terminfo database, or, when it is missing
+everywhere, installed into
+.I ~/.terminfo
+from the copy the binary carries (an entry curses cannot find makes
+editors exit on the spot and backspace guess).
+Only when even that write fails (no
+.BR $HOME ,
+read-only) do panes get
+.BR xterm-256color ,
+and everything still works.
 .TP
 .B SLOSH
 .B 1
diff --git a/include/slosh.h b/include/slosh.h
index 75aa658..47d8220 100644
--- a/include/slosh.h
+++ b/include/slosh.h
@@ -162,6 +162,10 @@ typedef struct {
 /* `cell_w`/`cell_h` are the client's cell size in pixels, so the pty's
  * winsize carries real pixel dimensions: a program that draws images asks the
  * tty how big a cell is, and zeroes there mean it cannot size one. */
+/* Write the embedded xterm-ghostty terminfo into ~/.terminfo (0 on
+ * success). Panes do this on their own when the entry is missing
+ * everywhere; `slosh --install-terminfo` is the by-hand spelling. */
+int pty_terminfo_install(void);
 int pty_spawn(pty_t *p, const char *const argv[], uint16_t cols, uint16_t rows,
               const char *cwd, uint16_t cell_w, uint16_t cell_h);
 int pty_resize(pty_t *p, uint16_t cols, uint16_t rows, uint16_t cell_w,
diff --git a/src/main.c b/src/main.c
index 3fdbfe6..838d6f7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -26,58 +26,18 @@
 #include "version.h"
 
 #ifndef _WIN32
-#include <errno.h>
-#include <sys/stat.h>
-
-#include "terminfo.h"
-
-/* Write the embedded xterm-ghostty terminfo entry into ~/.terminfo, which
- * is the first place curses looks: no root, no package, no conflict with a
- * ghostty the machine may install later (its own entry in the system
- * database simply stops being needed). Written under every name the entry
- * answers to, in the letter layout and Darwin's hashed one, because the
- * lookup is by filename. */
+/* The write itself lives in pty.c (pty_terminfo_install), because panes do
+ * it on their own when the entry is missing everywhere. This flag is the
+ * by-hand spelling, with a report around it. */
 static int install_terminfo(void) {
-  const char *home = getenv("HOME");
-  if (!home || !*home) {
-    fputs("slosh: no $HOME to install into\n", stderr);
+  if (pty_terminfo_install() != 0) {
+    fputs("slosh: could not write ~/.terminfo (no $HOME, or not writable)\n",
+          stderr);
     return 1;
   }
-  /* dir, then name inside it: x/ and 78/ for xterm-ghostty, g/ and 67/ for
-   * the ghostty alias. */
-  static const char *const spots[][2] = {
-      {"x", "xterm-ghostty"},
-      {"78", "xterm-ghostty"},
-      {"g", "ghostty"},
-      {"67", "ghostty"},
-  };
-  char path[1024];
-  snprintf(path, sizeof path, "%s/.terminfo", home);
-  if (mkdir(path, 0755) != 0 && errno != EEXIST) {
-    fprintf(stderr, "slosh: mkdir %s: %s\n", path, strerror(errno));
-    return 1;
-  }
-  for (size_t i = 0; i < sizeof spots / sizeof *spots; i++) {
-    snprintf(path, sizeof path, "%s/.terminfo/%s", home, spots[i][0]);
-    if (mkdir(path, 0755) != 0 && errno != EEXIST) {
-      fprintf(stderr, "slosh: mkdir %s: %s\n", path, strerror(errno));
-      return 1;
-    }
-    snprintf(path, sizeof path, "%s/.terminfo/%s/%s", home, spots[i][0],
-             spots[i][1]);
-    FILE *f = fopen(path, "wb");
-    if (!f || fwrite(TERMINFO_GHOSTTY, 1, sizeof TERMINFO_GHOSTTY, f) !=
-                  sizeof TERMINFO_GHOSTTY) {
-      fprintf(stderr, "slosh: write %s: %s\n", path, strerror(errno));
-      if (f) fclose(f);
-      return 1;
-    }
-    fclose(f);
-  }
-  printf("installed xterm-ghostty (and the ghostty alias) into %s/.terminfo\n"
+  printf("installed xterm-ghostty (and the ghostty alias) into ~/.terminfo\n"
          "new sessions use it; a session already running keeps the TERM it\n"
-         "chose at startup until it is restarted\n",
-         home);
+         "chose at startup until it is restarted\n");
   return 0;
 }
 #endif
diff --git a/src/pty.c b/src/pty.c
index f715acc..00fa190 100644
--- a/src/pty.c
+++ b/src/pty.c
@@ -8,6 +8,9 @@
 #include "slosh.h"
 
 #include <errno.h>
+#include <sys/stat.h>
+
+#include "terminfo.h"
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
@@ -33,6 +36,41 @@
  * lookup happens where it matters: panes run on the server's machine.
  *
  * Computed once, in the parent, before the first fork. */
+/* Write the embedded xterm-ghostty terminfo entry into ~/.terminfo, which
+ * is the first place curses looks: no root, no package, no conflict with a
+ * ghostty the machine may install later. Written under every name the
+ * entry answers to, in the letter layout and Darwin's hashed one, because
+ * the lookup is by filename. Quiet: pty_term() below calls this on its own
+ * when the entry is nowhere to be found, and `--install-terminfo` is the
+ * same write with a friendly report around it. */
+int pty_terminfo_install(void) {
+  const char *home = getenv("HOME");
+  if (!home || !*home) return -1;
+  static const char *const spots[][2] = {
+      {"x", "xterm-ghostty"},
+      {"78", "xterm-ghostty"},
+      {"g", "ghostty"},
+      {"67", "ghostty"},
+  };
+  char path[1024];
+  snprintf(path, sizeof path, "%s/.terminfo", home);
+  if (mkdir(path, 0755) != 0 && errno != EEXIST) return -1;
+  for (size_t i = 0; i < sizeof spots / sizeof *spots; i++) {
+    snprintf(path, sizeof path, "%s/.terminfo/%s", home, spots[i][0]);
+    if (mkdir(path, 0755) != 0 && errno != EEXIST) return -1;
+    snprintf(path, sizeof path, "%s/.terminfo/%s/%s", home, spots[i][0],
+             spots[i][1]);
+    FILE *f = fopen(path, "wb");
+    if (!f || fwrite(TERMINFO_GHOSTTY, 1, sizeof TERMINFO_GHOSTTY, f) !=
+                  sizeof TERMINFO_GHOSTTY) {
+      if (f) fclose(f);
+      return -1;
+    }
+    fclose(f);
+  }
+  return 0;
+}
+
 static bool term_add(char *dirs, size_t cap, size_t *n, const char *d) {
   if (!d || !*d) return false;
   int w = snprintf(dirs + *n, cap - *n, "%s%s", *n ? ":" : "", d);
@@ -74,6 +112,14 @@ static const char *pty_term(void) {
       break;
     }
   }
+
+  /* Nowhere at all: put our own copy in ~/.terminfo and use it. The write
+   * happens only when the entry is missing everywhere -- an entry that
+   * exists is somebody's, possibly newer than ours, and stays theirs. On a
+   * $HOME that cannot be written the fallback stands, and everything still
+   * works at xterm-256color. */
+  if (strcmp(cached, "xterm-256color") == 0 && pty_terminfo_install() == 0)
+    cached = "xterm-ghostty";
   return cached;
 }