From a2e466a874502b665807f620eb8edefb37be1e8c Mon Sep 17 00:00:00 2001
From: Gabriel Schneider <gbrls@0x4200.cafe>
Date: Tue, 29 Sep 2026 13:45:25 -0300
Subject: A ThemeFile that cannot be read or is no theme fails its write, and a
 bad path says why

The theme is read when the host performs the request, after the write had been answered, so a missing file or a bad theme only showed a message; and a path not ending .zon said only invalid theme path. Load failures are now the waiting write's (late, as a Save's), and the path refusal says a theme file is a .zon.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/builtins.zig   | 12 ++++++++----
 src/file_watch.zig |  9 ++++++++-
 test/fs.py         |  9 +++++++++
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/builtins.zig b/src/builtins.zig
index ca01e0fe..ec6afeae 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -808,10 +808,14 @@ pub const ThemeFile = struct {
     pub const requires_arg = true;
     pub const enabled = pardes.hosted;
     pub fn run(c: Ctx) void {
-        if (comptime enabled)
-            colors.requestThemeFile(c.p, c.id, c.arg orelse return)
-        else
-            unreachable;
+        if (comptime !enabled) unreachable;
+        const arg = std.mem.trim(u8, c.arg orelse return, " \t\r\n");
+        // Said with why, not "invalid theme path".
+        if (!std.mem.endsWith(u8, arg, ".zon")) {
+            var said: [320]u8 = undefined;
+            return c.p.reportFailure(c.id, std.fmt.bufPrint(&said, "ThemeFile: {s}: invalid theme path: a theme file is a .zon (DumpThemes writes some to start from)", .{arg[0..@min(arg.len, 200)]}) catch "ThemeFile: invalid theme path: a theme file is a .zon");
+        }
+        colors.requestThemeFile(c.p, c.id, arg);
     }
 };
 
diff --git a/src/file_watch.zig b/src/file_watch.zig
index 81f4ba87..148bc836 100644
--- a/src/file_watch.zig
+++ b/src/file_watch.zig
@@ -576,12 +576,19 @@ pub fn applyThemeEffect(
     watchPath(fd, watches, theme_slot, null, 0, .{ .text = 0 });
     if (!on) return false;
     const request = colors.themeFileRequest(core, generation) orelse return false;
+    // What fails here is the ThemeFile write's failure too, which waits on
+    // this (the one-failure rule): late, as a Save's.
+    const pane = request.pane;
     const bytes = filesystem.readFile(gpa, request.path) catch |err| {
         colors.failThemeFile(core, generation, err);
+        core.noteLateFailure(pane);
         return false;
     };
     defer gpa.free(bytes);
-    if (!colors.loadThemeFile(core, generation, bytes, animate)) return false;
+    if (!colors.loadThemeFile(core, generation, bytes, animate)) {
+        core.noteLateFailure(pane);
+        return false;
+    }
     const hash = std.hash.Wyhash.hash(0, bytes);
     watchPath(fd, watches, theme_slot, request.path, generation, .{ .text = hash });
     if (watches[theme_slot] == null) return false;
diff --git a/test/fs.py b/test/fs.py
index a025ec47..8047273d 100644
--- a/test/fs.py
+++ b/test/fs.py
@@ -836,6 +836,15 @@ def odd_paths(binary):
                         pass
                     assert client.read('/index'), (where, line)
             client.write('/ctl', b'DumpDir\n')
+            # A theme file that is not there, or no theme, fails the write.
+            (root / 'bad.zon').write_bytes(b'.{ .nonsense = 1 }')
+            for line, why in ((f'ThemeFile {root}/missing.zon', 'theme file'), (f'ThemeFile {root}/bad.zon', 'theme file'),
+                              ('ThemeFile notes.txt', 'a theme file is a .zon')):
+                try:
+                    client.write('/ctl', (line + '\n').encode())
+                    raise AssertionError(f'{line} was taken')
+                except OSError as refused:
+                    assert why in str(refused), (line, refused)
 
 
 def cut_writes(binary):
-- 
cgit v1.3