From 81de981f263ec32ac977ecfd7519c4a6e39b4935 Mon Sep 17 00:00:00 2001
From: Marc Jakobi <marc.jakobi@tiko.energy>
Date: Fri, 22 Dec 2023 17:34:28 +0100
Subject: [PATCH] feat: `viewHir` command

Closes #15.
---
 CHANGELOG.md                       |  6 ++++
 README.md                          | 17 ++++++++++++
 lua/rustaceanvim/commands/hir.lua  | 44 ++++++++++++++++++++++++++++++
 lua/rustaceanvim/commands/init.lua |  3 ++
 4 files changed, 70 insertions(+)
 create mode 100644 lua/rustaceanvim/commands/hir.lua

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e5c5b4a6..aa239e7d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- LSP: `viewHir` command [[#14](https://github.com/mrcjkb/rustaceanvim/issues/14)].
+
 ## [3.10.5] - 2023-12-22
 
 ### Fixed
diff --git a/README.md b/README.md
index c0e80693..7031047f 100644
--- a/README.md
+++ b/README.md
@@ -386,6 +386,23 @@ for more configuration options.
 
 </details>
 
+<details>
+  <summary>
+	<b>View Hir</b>
+  </summary>
+
+  Opens a buffer with a textual representation of the HIR
+  of the function containing the cursor.
+  Useful for debugging or when working on rust-analyzer itself.
+  
+  ```vimscript
+  :RustLsp viewHir
+  ```
+  ```lua
+  vim.cmd.RustLsp('viewHir')
+  ```
+</details>
+
 <!-- markdownlint-restore -->
 
 ## Advanced configuration
diff --git a/lua/rustaceanvim/commands/hir.lua b/lua/rustaceanvim/commands/hir.lua
new file mode 100644
index 00000000..674e24a2
--- /dev/null
+++ b/lua/rustaceanvim/commands/hir.lua
@@ -0,0 +1,44 @@
+local M = {}
+
+local rl = require('rustaceanvim.rust_analyzer')
+local ui = require('rustaceanvim.ui')
+
+---@type integer | nil
+local latest_buf_id = nil
+
+local function handler(err, result)
+  if err then
+    vim.notify('viewHir failed' .. result and ': ' .. result or '', vim.log.levels.ERROR)
+    return
+  end
+  if result and result:match('Not inside a function body') then
+    vim.notify('viewHir failed: Not inside a function body', vim.log.levels.ERROR)
+    return
+  elseif type(result) ~= 'string' then
+    vim.notify('viewHir failed: ' .. vim.inspect(result), vim.log.levels.ERROR)
+  end
+
+  -- check if a buffer with the latest id is already open, if it is then
+  -- delete it and continue
+  ui.delete_buf(latest_buf_id)
+
+  -- create a new buffer
+  latest_buf_id = vim.api.nvim_create_buf(false, true) -- not listed and scratch
+
+  -- split the window to create a new buffer and set it to our window
+  ui.split(true, latest_buf_id)
+
+  local lines = vim.split(result, '\n')
+
+  -- set filetype to rust for syntax highlighting
+  vim.bo[latest_buf_id].filetype = 'rust'
+  -- write the expansion content to the buffer
+  vim.api.nvim_buf_set_lines(latest_buf_id, 0, 0, false, lines)
+end
+
+function M.hir()
+  local position_params = vim.lsp.util.make_position_params(0, nil)
+  rl.buf_request(0, 'rust-analyzer/viewHir', position_params, handler)
+end
+
+return M.hir
diff --git a/lua/rustaceanvim/commands/init.lua b/lua/rustaceanvim/commands/init.lua
index fb5a7db9..675ffa95 100644
--- a/lua/rustaceanvim/commands/init.lua
+++ b/lua/rustaceanvim/commands/init.lua
@@ -102,6 +102,9 @@ local command_tbl = {
     local cmd = args[1] or 'run'
     require('rustaceanvim.commands.fly_check')(cmd)
   end,
+  viewHir = function()
+    require('rustaceanvim.commands.hir')()
+  end,
   logFile = function()
     vim.cmd.e(config.server.logfile)
   end,