Add diff viewing

DIFF_FEATURE.md

@@ -0,0 +1,245 @@
+# OpenCode Diff Review Feature
+
+This feature provides PR-style review of changes made by OpenCode, allowing you to review, navigate, and accept/reject file edits.
+
+## Overview
+
+OpenCode supports **two different diff viewing modes** to suit your preferences:
+
+### 1. Enhanced Mode (Default - No Dependencies)
+
+Uses vim's built-in diff-mode with side-by-side comparison and a custom file panel. **This is the default mode** - works out of the box!
+
+**Features:**
+- Side-by-side diff with syntax highlighting
+- Custom file panel showing all changed files
+- Per-hunk staging with `a`/`r` keymaps
+- File navigation with `<Tab>`/`<S-Tab>`
+- Hunk navigation with `]x`/`[x`
+- Single tab for all files
+- No external dependencies required
+
+**Configuration:**
+```lua
+vim.g.opencode_opts = {
+  events = {
+    session_diff = {
+      diff_mode = "enhanced",  -- This is the default
+    },
+  },
+}
+```
+
+### 2. Unified Mode (Minimal)
+
+Simple unified diff view in a single buffer for lightweight reviews.
+
+**Features:**
+- Minimal UI
+- Unified diff format (like `git diff`)
+- File-level accept/reject
+- Lightweight and fast
+
+**Configuration:**
+```lua
+vim.g.opencode_opts = {
+  events = {
+    session_diff = {
+      diff_mode = "unified",
+    },
+  },
+}
+```
+
+## Keybindings
+
+### Enhanced Mode
+
+**Diff View:**
+- `gp` - Toggle file panel
+- `<Tab>` - Next file
+- `<S-Tab>` - Previous file
+- `]x` - Next hunk
+- `[x` - Previous hunk
+- `a` - Accept current hunk (keep change)
+- `r` - Reject current hunk (revert change)
+- `A` - Accept all hunks in current file
+- `R` - Revert entire current file
+- `q` - Close diff view
+
+**File Panel:**
+- `<Enter>` - Jump to selected file
+- `gp` - Close panel
+- `q` - Close diff view
+
+### Unified Mode
+
+- `n` - Next file
+- `p` - Previous file
+- `a` - Accept this file (keep changes)
+- `r` - Reject this file (revert to original)
+- `A` - Accept all files
+- `R` - Reject all files
+- `q` - Close review
+
+## Per-Hunk Staging
+
+**Enhanced mode** supports per-hunk accept/reject operations, allowing you to selectively keep or discard individual changes within a file.
+
+**Accept Hunk (`a`):**
+1. Position cursor on a hunk you want to keep
+2. Press `a` to accept
+3. Hunk disappears from diff (both sides now match)
+4. Change is kept in the actual file
+
+**Reject Hunk (`r`):**
+1. Position cursor on a hunk you want to revert
+2. Press `r` to reject  
+3. Hunk disappears from diff (both sides now match)
+4. Change is reverted in the actual file
+
+**Accept All (`A`):**
+- Accept all remaining hunks in the current file
+- All changes are kept
+
+**Implementation:** Uses vim's built-in diff commands (`diffput` to accept, `diffget` to reject).
+
+## Configuration
+
+**Full configuration options:**
+
+```lua
+vim.g.opencode_opts = {
+  events = {
+    session_diff = {
+      enabled = true,           -- Enable diff review (default: true)
+      diff_mode = "enhanced",   -- "enhanced" | "unified" (default: "enhanced")
+      open_in_tab = false,      -- For unified mode (default: false)
+    },
+  },
+}
+```
+
+**Disable diff review:**
+
+```lua
+vim.g.opencode_opts = {
+  events = {
+    session_diff = {
+      enabled = false,
+    },
+  },
+}
+```
+
+## File Panel
+
+### Enhanced Mode Panel
+
+Shows a list of changed files with stats:
+
+```
+OpenCode Changed Files
+────────────────────────────────────────
+
+▶ 1. config.lua +12 -5
+  2. diff.lua +87 -34
+  3. health.lua +8 -15
+
+────────────────────────────────────────
+Keymaps:
+  <Enter>  Jump to file
+  <Tab>    Next file
+  <S-Tab>  Previous file
+  ]x       Next hunk
+  [x       Previous hunk
+  a        Accept hunk
+  r        Reject hunk
+  A        Accept all hunks
+  gp       Toggle panel
+  R        Revert file
+  q        Close diff
+```
+
+- **Dynamic width**: 20% of screen (minimum 25 columns)
+- **▶ marker**: Shows current file
+- **Stats**: `+additions -deletions` for each file
+- **Full keymap reference**: Built into panel footer
+
+## Health Check
+
+Run `:checkhealth opencode` to verify your configuration:
+
+**Enhanced mode:**
+```
+opencode.nvim [diff review]
+  - OK: Session diff review is enabled.
+  - OK: Diff mode: Enhanced (side-by-side vim diff-mode with file panel)
+```
+
+**Unified mode:**
+```
+opencode.nvim [diff review]
+  - OK: Session diff review is enabled.
+  - OK: Diff mode: Unified (simple unified diff view)
+```
+
+## Mode Comparison
+
+| Feature | Enhanced | Unified |
+|---------|----------|---------|
+| **Dependencies** | None | None |
+| **UI Quality** | ⭐⭐⭐⭐ | ⭐⭐ |
+| **File Panel** | Custom | None |
+| **Side-by-side** | ✅ | ❌ |
+| **Per-hunk staging** | ✅ | ❌ |
+| **File navigation** | ✅ | ✅ |
+| **Hunk navigation** | ✅ | ❌ |
+| **Syntax highlighting** | ✅ | Limited |
+
+**Recommendations:**
+- **Best UX**: Use `diff_mode = "enhanced"` (default) - great UX without any plugins
+- **Minimal**: Use `diff_mode = "unified"` for simple, lightweight reviews
+
+## How It Works
+
+1. **AI makes edits** across multiple files
+2. **Files are written** to disk immediately  
+3. **`message.updated` event fires** with change data
+4. **Diff mode determined** from config
+5. **Review UI opens** automatically based on mode:
+   - **Enhanced**: Custom vim diff-mode implementation
+   - **Unified**: Simple unified diff buffer
+6. **Navigate and stage:**
+   - Use keymaps to navigate files/hunks
+   - Accept or reject individual hunks (enhanced mode)
+   - Changes persist immediately to disk
+
+**Restore Strategy:** All modes use the `before` content from the event (no Git required):
+
+```lua
+-- To revert a file:
+vim.fn.writefile(vim.split(file_data.before, "\n"), file_data.file)
+
+-- To revert a hunk:
+vim.cmd("diffget")  -- Pull original from "before" buffer
+vim.cmd("write")
+```
+
+## Files
+
+**Core Implementation:**
+- `plugin/events/session_diff.lua` - Event listener
+- `lua/opencode/diff.lua` - Both diff modes
+- `lua/opencode/config.lua` - Configuration
+- `lua/opencode/health.lua` - Health check
+
+## Future Enhancements
+
+- [x] Side-by-side vim diff-mode view
+- [x] File panel for navigation
+- [x] Per-hunk accept/reject (staging)
+- [ ] Configurable keybindings
+- [ ] Auto-close after accepting all
+- [ ] File filtering/search in panel
+- [ ] Custom diff algorithms

debug_events.lua

@@ -0,0 +1,14 @@
+-- Debug helper: Add this to your Neovim config temporarily to see ALL opencode events
+
+vim.api.nvim_create_autocmd("User", {
+  pattern = "OpencodeEvent:*",
+  callback = function(args)
+    local event = args.data.event
+    vim.notify(
+      string.format("[EVENT] %s\nProperties: %s", event.type, vim.inspect(event.properties or {})),
+      vim.log.levels.INFO,
+      { title = "opencode.debug" }
+    )
+  end,
+  desc = "Debug all opencode events",
+})

lua/opencode/config.lua

@@ -111,6 +111,14 @@ local defaults = {
       enabled = true,
       idle_delay_ms = 1000,
     },
+    session_diff = {
+      enabled = true, -- Show session review for session.diff events
+      -- Diff mode: "enhanced" | "unified"
+      -- "enhanced": Use vim diff-mode side-by-side with file panel (default)
+      -- "unified": Simple unified diff view (minimal, fallback option)
+      diff_mode = "enhanced",
+      open_in_tab = false, -- Open review in a new tab (and reuse the same tab for navigation)
+    },
   },
   provider = {
     cmd = "opencode",