gtk+3: im-quartz IM module not loaded (GTK_IM_MODULE_FILE required for Japanese input on macOS)

[shumoku88-bit]

Description

On macOS Sequoia (15.x), the GTK+3 Homebrew package includes im-quartz.so (the macOS native input method bridge), but GTK's module loader fails to find immodules.cache at runtime. As a result, im_module_init() is never called, and Japanese/Chinese/Korean input does not work in GTK3 apps (e.g., gedit).

Workaround

Setting GTK_IM_MODULE_FILE explicitly resolves the module loading issue:

export GTK_IM_MODULE=quartz
export GTK_IM_MODULE_FILE=/usr/local/lib/gtk-3.0/3.0.0/immodules.cache

Diagnosis

• im-quartz.so is present at /usr/local/Cellar/gtk+3/3.24.52/lib/gtk-3.0/3.0.0/immodules/im-quartz.so
• immodules.cache exists at /usr/local/lib/gtk-3.0/3.0.0/immodules.cache and correctly references im-quartz.so
• Without GTK_IM_MODULE_FILE, GtkIMMulticontext falls back to gtk-im-context-simple and im_module_init() is never called (verified via ctypes)
• With GTK_IM_MODULE_FILE set, the quartz IM context loads and initializes correctly

Expected behavior

GTK should find immodules.cache automatically without requiring GTK_IM_MODULE_FILE to be set.

Environment

• macOS Sequoia (Darwin 24.6.0)
• gtk+3 3.24.52 (Homebrew bottle)
• Quartz backend (-Dquartz_backend=true -Dx11_backend=false)
• JIS keyboard with Japanese (Kotoeri Romaji) input source enabled

Possible fix

The formula's post-install step or the module cache path search in GTK may need adjustment for the Homebrew Cellar/symlink layout on macOS.