go-edit

A code editor widget for go-gui. Pure Go, no CGO. Syntax highlighting via chroma. Text shaping via go-glyph.

npad — the kitchen-sink example application

---

Features

• Buffer — per-line byte store; UTF-8 aware; grapheme-cluster cursor movement
• Syntax highlighting — chroma v2; per-line token cache; language autodetect from filename and content
• Selection — mouse drag, double-click word, triple-click line; Shift+arrow
• Multi-cursor — Alt-click to add; Ctrl+D selects next match; Escape collapses
• Undo / redo — linear stack; typing coalesced within 500 ms; compound-edit groups
• Search / replace — find bar drawn inside the canvas; literal or regex; case toggle; find-in-selection; replace all (single undo entry)
• File I/O — EOL detect and preserve (LF / CRLF / CR); encoding detect and round-trip (UTF-8, UTF-16 LE/BE, Latin-1, CP1252, BOM); atomic save; external-change watch; indent autodetect
• Bracket matching — highlight + jump; auto-close pairs
• Code folding — indent-based; gutter click to toggle
• Line wrap — toggleable; word-boundary break; cursor column math preserved across wrapped rows
• Whitespace visualization — spaces, tabs, EOL markers; cycles None / All / Selection
• Sticky scroll — pinned scope headers at viewport top; syntax-highlighted
• Diagnostics API — gutter markers and squiggles; callers push DecoGutter / DecoSquiggle decorations; no LSP dependency in core
• Extension substrate — EditFilter chain, PostEditFunc observers, MarkSet position tracker, DecorationProvider interface, layered KeymapStack
• Theme — derived from go-gui theme; per-token color overrides; chroma style bridge
• IME — preedit inline virtual text; candidate window anchoring via w.IMESetRect
• Cursor blink — injectable clock; separate draw canvas so blink doesn't bust the tessellation cache
• Drag-and-drop — file open via OnFileDrop
• Accessibility — AccessRoleTextArea; label and state wired to go-gui a11y tree
• Help overlay — F1 shows keybinding reference; scrollable; dismisses on Esc

File size limit: 32 MiB. Headless-testable; no backend required for unit tests.

---

Usage

import (
    "github.com/mike-ward/go-edit/edit"
    "github.com/mike-ward/go-edit/edit/buffer"
    "github.com/mike-ward/go-edit/edit/highlight"
)

buf := buffer.New()
hl  := highlight.New(buf, nil) // nil → autodetect language

view := edit.Editor(edit.EditorCfg{
    Buffer:          buf,
    DecoProviders:   []buffer.DecorationProvider{hl},
    ShowLineNumbers: true,
    IDFocus:         1,
})

Editor returns a gui.View and fits into any go-gui layout. Multiple editors per window are supported; each is keyed by IDFocus.

Running the example

go run ./examples/npad [file]

npad demonstrates native menus, file I/O, dirty-state tracking, syntax highlighting, theme switching, and a status bar. It requires the CGO backend (SDL2, Freetype).

---

Architecture

edit/buffer/   — Buffer, Edit/Change, undo, marks, filters, decorations
edit/highlight/ — chroma DecorationProvider
edit/text/     — TextMeasurer wrapper; XForColumn / ColumnForX
edit/          — Editor factory; draw, input, amend closures; keymap; actions
edit/internal/fakewin/ — headless test fixture (deterministic measurer, event builders)
examples/npad/ — full-featured example application

Key design points:

• OnDraw has no *Window access. Everything the draw path needs is closed over at AmendLayout time into *editorFrameData.
• DrawCanvas is sized to the viewport; editorState.ScrollY owns scroll. The go-gui Column(IDScroll) mechanism is not used.
• Buffer.Apply(Edit) is the single mutation choke point. Filters, observers, and undo all route through it.
• ID: "" on the DrawCanvas bypasses go-gui's (shape.ID, shape.Version) render cache, which is necessary because buffer/cursor/scroll change every frame.

---

Development

Tests run fully headless:

go test ./edit/...
go test -race ./edit/...
go test -bench=. -benchmem -run='^$' ./edit/buffer/
go test -fuzz=FuzzBufferApply -fuzztime=30s ./edit/buffer/
go vet ./...
golangci-lint run

Local development against sibling checkouts of go-gui and go-glyph: add replace directives to go.mod pointing at ../go-gui and ../go-glyph. Strip before tagging.

---

License

MIT. See LICENSE.