diff support in treesitter/fold

lua/options.lua

@@ -24,6 +24,18 @@ vim.api.nvim_create_autocmd({ "FocusGained", "BufEnter", "CursorHold", "CursorHo
     command = "if mode() != 'c' | checktime | endif",
 })
 
+-- `git show`/`git diff`/`git log -p` piped into nvim (e.g. `git show <hash> | nvim -`)
+-- arrive as stdin with no filename, so normal filetype detection never fires
+-- and folding/highlighting silently stay off. Sniff the content instead.
+vim.api.nvim_create_autocmd("StdinReadPost", {
+    callback = function()
+        local first = vim.fn.getline(1)
+        if first:match("^commit %x+") or first:match("^diff %-%-git ") or first:match("^From %x+") then
+            vim.bo.filetype = "diff"
+        end
+    end,
+})
+
 vim.filetype.add({ extension = { asm = "asm", s = "asm", S = "asm" } })
 vim.api.nvim_create_autocmd("FileType", {
     pattern = "asm",

lua/plugins.lua

@@ -275,7 +275,7 @@ require("nvim-treesitter").install({
     "lua", "vim", "vimdoc", "bash", "c", "cpp", "rust", "python",
     "javascript", "typescript", "tsx", "svelte", "css", "html",
     "json", "toml", "yaml", "markdown", "markdown_inline",
-    "java", "typst", "vala",
+    "java", "typst", "vala", "diff",
 })
 
 vim.api.nvim_create_autocmd("FileType", {