fix: Improved more accurate diffing strategy

Previously source was rebased on target, then check diff to target;
this is not how ADO does things, and it leads to incorrect comment
positions.

Now we get the common ancestor commit, and do the diff to that commit.
No more rebasing is required.

lua/adopure/activate.lua

@@ -6,8 +6,8 @@ local function confirm_open_in_diffview(pull_request)
         if not input then
             return
         end
-        local remote_target_name = "origin/" .. vim.split(pull_request.targetRefName, "refs/heads/")[2]
-        vim.cmd(":DiffviewOpen " .. remote_target_name)
+        local merge_base = require("adopure.git").get_merge_base(pull_request)
+        vim.cmd(":DiffviewOpen " .. merge_base)
     end)
 end
 

lua/adopure/git.lua

@@ -67,6 +67,28 @@ function M.get_remote_config()
     return extract_git_details(elected_remote)
 end
 
+---Get merge base commit
+---@param pull_request adopure.PullRequest
+---@return string merge_base
+function M.get_merge_base(pull_request)
+    local get_merge_base = require("plenary.job"):new({
+        command = "git",
+        args = { "merge-base", pull_request.lastMergeSourceCommit.commitId, pull_request.lastMergeTargetCommit.commitId },
+        cwd = ".",
+    })
+    get_merge_base:start()
+    local result = require("adopure.utils").await_result(get_merge_base)
+    if result.stderr[1] then
+        if not result.stdout[1] then
+            error(result.stderr[1])
+        end
+        vim.notify(result.stderr[1], 3)
+    end
+    assert(result.stdout[1], "No merge base found;")
+    return result.stdout[1]
+end
+
+
 ---@param pull_request adopure.PullRequest
 ---@param open_callable function
 function M.confirm_checkout_and_open(pull_request, open_callable)
@@ -76,11 +98,10 @@ function M.confirm_checkout_and_open(pull_request, open_callable)
             open_callable()
             return
         end
-        local remote_source_name = "origin/" .. vim.split(pull_request.sourceRefName, "refs/heads/")[2]
 
         local git_checkout_remote_job = Job:new({
             command = "git",
-            args = { "checkout", remote_source_name },
+            args = { "checkout", pull_request.lastMergeSourceCommit.commitId },
             cwd = ".",
             on_exit = function(j, return_val)
                 if return_val ~= 0 then
@@ -89,29 +110,6 @@ function M.confirm_checkout_and_open(pull_request, open_callable)
             end,
         })
 
-        local remote_target_name = "origin/" .. vim.split(pull_request.targetRefName, "refs/heads/")[2]
-        local git_rebase_abort_job = Job:new({
-            command = "git",
-            args = { "rebase", "--abort" },
-            cwd = ".",
-            on_exit = function(j, return_val)
-                if return_val ~= 0 then
-                    error("Rebase abort failed: " .. vim.inspect(j:result()))
-                end
-            end,
-        })
-        local git_rebase_job = Job:new({
-            command = "git",
-            args = { "rebase", remote_target_name },
-            cwd = ".",
-            on_exit = function(j, return_val)
-                if return_val ~= 0 then
-                    git_rebase_abort_job:start()
-                    error("Rebase failed: " .. vim.inspect(j:result()))
-                end
-            end,
-        })
-        git_checkout_remote_job:and_then_on_success(git_rebase_job)
         git_checkout_remote_job:start()
         open_callable()
     end)

lua/adopure/types.lua

@@ -15,8 +15,14 @@
 ---@field createdBy adopure.User
 ---@field creationDate string
 ---@field mergeStatus string
+---@field lastMergeCommit MergeCommit
+---@field lastMergeSourceCommit MergeCommit
+---@field lastMergeTargetCommit MergeCommit
 ---@field reviewers adopure.Reviewer[]
 
+---@class MergeCommit
+---@field commitId string
+
 ---@class adopure.User
 ---@field displayName string
 ---@field id string