From 12cb20d154dd4ccbb5144855ebdba96e97fb68f6 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <62671086+barrettruth@users.noreply.github.com>
Date: Thu, 5 Mar 2026 22:26:28 -0500
Subject: [PATCH] feat: add `extra_args` provider field (#51)

* feat: add `extra_args` provider field

Problem: Overriding a single flag (e.g. `-outdir=build`) required
redefining the entire `args` function, duplicating all preset defaults.

Solution: Add `extra_args` field that appends to the resolved `args`
after evaluation. Accepts a static table or a context function.

* docs: document `extra_args` provider field
---
 doc/preview.txt          | 4 ++++
 lua/preview/compiler.lua | 3 +++
 lua/preview/init.lua     | 2 ++
 3 files changed, 9 insertions(+)

diff --git a/doc/preview.txt b/doc/preview.txt
index 383a8f5..b4b74f5 100644
--- a/doc/preview.txt
+++ b/doc/preview.txt
@@ -68,6 +68,10 @@ Provider fields: ~
                                         receives a |preview.Context| and
                                         returns a string[].
 
+  {extra_args}       (string[]|function) Appended to {args} after evaluation.
+                                        Useful for adding flags to a preset
+                                        without replacing its defaults.
+
   {cwd}              (string|function)  Working directory. If a function,
                                         receives a |preview.Context|.
                                         Default: git root or file directory.
diff --git a/lua/preview/compiler.lua b/lua/preview/compiler.lua
index a193ad2..3e8de12 100644
--- a/lua/preview/compiler.lua
+++ b/lua/preview/compiler.lua
@@ -309,6 +309,9 @@ function M.compile(bufnr, name, provider, ctx, opts)
   if provider.args then
     vim.list_extend(cmd, eval_list(provider.args, resolved_ctx))
   end
+  if provider.extra_args then
+    vim.list_extend(cmd, eval_list(provider.extra_args, resolved_ctx))
+  end
 
   log.dbg('compiling buffer %d with provider "%s": %s', bufnr, name, table.concat(cmd, ' '))
 
diff --git a/lua/preview/init.lua b/lua/preview/init.lua
index 7cb982b..489679f 100644
--- a/lua/preview/init.lua
+++ b/lua/preview/init.lua
@@ -2,6 +2,7 @@
 ---@field ft? string
 ---@field cmd string[]
 ---@field args? string[]|fun(ctx: preview.Context): string[]
+---@field extra_args? string[]|fun(ctx: preview.Context): string[]
 ---@field cwd? string|fun(ctx: preview.Context): string
 ---@field env? table<string, string>
 ---@field output? string|fun(ctx: preview.Context): string
@@ -94,6 +95,7 @@ function M.setup(opts)
     vim.validate(prefix .. '.cmd', provider.cmd, 'table')
     vim.validate(prefix .. '.cmd[1]', provider.cmd[1], 'string')
     vim.validate(prefix .. '.args', provider.args, { 'table', 'function' }, true)
+    vim.validate(prefix .. '.extra_args', provider.extra_args, { 'table', 'function' }, true)
     vim.validate(prefix .. '.cwd', provider.cwd, { 'string', 'function' }, true)
     vim.validate(prefix .. '.output', provider.output, { 'string', 'function' }, true)
     vim.validate(prefix .. '.error_parser', provider.error_parser, 'function', true)