fix: suppress V compiler errors for unused params and mutable interface casts

[quaesitor-scientiam]

Summary

• Rename unused callback parameters to _ to silence V's "declared but never used" errors (accordion, alpha, colorbox, colorsliders, gg_app, grid, rasterview, splitpanel, tabs)
• Fix fontchooser_lb_change: declare fc as mut so the DrawTextWidget cast on fc.dtw is valid
• Fix hideable_add_shortcut: use unsafe{} for Shortcutable cast from immutable &ui.Window
• Fix src/chunkview.v: wrap DrawTextWidget(cv) casts in unsafe{} where cv is &ChunkView
• Fix src/layout_canvas.v: same unsafe{} treatment for DrawTextWidget(c) from &CanvasLayout

Context

These are all hard compile errors under the current V compiler (as of April 2026). The unsafe{} casts for DrawTextWidget are necessary because V's checker now rejects creating a mutable interface value from an immutable pointer (&T). The underlying data is heap-allocated and valid; unsafe{} tells the compiler to trust the programmer's intent here.

This PR is part of effort to restore the v-apps-compile CI job in vlang/v — tracked at vlang/v#26853.

Test plan

• Compile vlang/ui with latest V: v .
• Verify no unused-variable or immutability errors

🤖 Generated with Claude Code

[JalonSolov]

Need to run v fmt -w . to format a bunch of the files.

Suggest also running v git-fmt-hook install in your clone so files are auto-formatted on commit.

[Wajinn]

Appears to be an issue for both VUI and GUI (Linux box).

[quaesitor-scientiam]

Good catch — ran v fmt -w . across the whole repo. Only component/demo.v needed a change (one indentation fix). Updated in dcc443f.

[JalonSolov]

More than one file needed to be formatted. From most recent CI run:

/home/runner/work/ui/ui/ui/libvg/raster_tool.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/textbox_textview.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/layout_canvas.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/grid.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/tool_draw.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/ui.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/picture.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/button.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/tool_mouse.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/native_widgets_darwin.c.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/tool_gg.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/stack.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/menu.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/widget_checkbox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/interface_scrollable.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/listbox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/extra_text_syntax.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/label.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/dropdown.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/textbox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/switch.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/extra_debug.v is not vfmt'ed
/home/runner/work/ui/ui/ui/src/native_widgets_windows.c.v is not vfmt'ed
/home/runner/work/ui/ui/ui/bin/vui_png.v is not vfmt'ed
/home/runner/work/ui/ui/ui/examples/demo_text_width_additive.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/grid.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/colorsliders.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/subwindow_messagebox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/colorpalette.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/menufile.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/colorbox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/double_listbox.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/rasterview.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/tabs.v is not vfmt'ed
/home/runner/work/ui/ui/ui/component/treeview.v is not vfmt'ed
/home/runner/work/ui/ui/ui/apps/v2048/2048.v is not vfmt'ed

[quaesitor-scientiam]

Thanks for the detailed CI output.

On the fmt failures: All 36 files were already failing v fmt -verify on the upstream master branch before this PR (confirmed by checking the CI run on commit 5702e61, April 13). The local V on Windows (both stable 134cf90 and release 0c3183c) reports all files as already formatted, but the CI's Linux V disagrees — this is a pre-existing cross-platform vfmt discrepancy on the upstream master. Our PR actually fixed component/demo.v (it was in the 37 failures on master; no longer listed). We are not introducing any new fmt failures.

On the build errors: The latest commit (76c47f5) addresses the remaining issues in files we changed:

• lb_mouse_up, slider_mouse_up, sw_mouse_up — unused e (MouseEvent) renamed to _
• DrawTextWidget() calls in immutable-receiver functions in listbox.v and textbox.v — wrapped in unsafe{}, following the existing pattern in this codebase (e.g. widget: unsafe { w } in interface_scrollable.v)

The remaining build failures (extra_size.v, interface_drag_drop.v, interface_scrollable.v, textbox_textview.v) are in files this PR does not touch — they are pre-existing issues on the upstream master.