os: add resourcesDir function to find app resource dir

src/os/main.zig

@@ -7,6 +7,7 @@ pub usingnamespace @import("homedir.zig");
 pub usingnamespace @import("locale.zig");
 pub usingnamespace @import("macos_version.zig");
 pub usingnamespace @import("mouse.zig");
+pub usingnamespace @import("resourcesdir.zig");
 pub const TempDir = @import("TempDir.zig");
 pub const passwd = @import("passwd.zig");
 pub const xdg = @import("xdg.zig");

src/os/resourcesdir.zig

@@ -0,0 +1,74 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const Allocator = std.mem.Allocator;
+
+/// Gets the directory to the bundled resources directory, if it
+/// exists (not all platforms or packages have it). The output is
+/// written to the given buffer if we need to allocate. Note that
+/// the output is not ALWAYS written to the buffer and may refer to
+/// static memory.
+///
+/// This returns error.OutOfMemory is buffer is not big enough.
+pub fn resourcesDir(buf: []u8) !?[]const u8 {
+    // If we have an environment variable set, we always use that.
+    if (std.os.getenv("GHOSTTY_RESOURCES_DIR")) |dir| {
+        if (dir.len > 0) {
+            return dir;
+        }
+    }
+
+    // This is the sentinel value we look for in the path to know
+    // we've found the resources directory.
+    const sentinel = "terminfo/ghostty.termcap";
+
+    // Get the path to our running binary
+    var exe_buf: [std.fs.MAX_PATH_BYTES]u8 = undefined;
+    var exe: []const u8 = std.fs.selfExePath(&exe_buf) catch return null;
+
+    // We have an exe path! Climb the tree looking for the terminfo
+    // bundle as we expect it.
+    while (std.fs.path.dirname(exe)) |dir| {
+        exe = dir;
+
+        // On MacOS, we look for the app bundle path.
+        if (comptime builtin.target.isDarwin()) {
+            if (try maybeDir(buf, dir, "Contents/Resources", sentinel)) |v| {
+                return v;
+            }
+        }
+
+        // On all platforms, we look for a /usr/share style path. This
+        // is valid even on Mac since there is nothing that requires
+        // Ghostty to be in an app bundle.
+        if (try maybeDir(buf, dir, "share", sentinel)) |v| {
+            return v;
+        }
+    }
+
+    return null;
+}
+
+/// Little helper to check if the "base/sub/suffix" directory exists and
+/// if so return true. The "suffix" is just used as a way to verify a directory
+/// seems roughly right.
+///
+/// "buf" must be large enough to fit base + sub + suffix. This is generally
+/// MAX_PATH_BYTES so its not a big deal.
+pub fn maybeDir(
+    buf: []u8,
+    base: []const u8,
+    sub: []const u8,
+    suffix: []const u8,
+) !?[]const u8 {
+    const path = try std.fmt.bufPrint(&buf, "{s}/{s}/{s}", .{ base, sub, suffix });
+
+    if (std.fs.accessAbsolute(path, .{})) {
+        const len = path.len - suffix.len - 1;
+        return buf[0..len];
+    } else |_| {
+        // Folder doesn't exist. If a different error happens its okay
+        // we just ignore it and move on.
+    }
+
+    return null;
+}