fix: renameしたファイルをFudeReviewDiffで旧パスと比較する

.claude/review-lessons.md

@@ -149,3 +149,8 @@
 - **問題**: 「同一性ガードはコールバック先頭に置く」というルールの先例として`init.reload`を挙げたが、実際には各取得コールバックの更新条件内と完了バリア後で確認する構造で、ルールの参照先と説明が食い違っていた。`captured_state`をgrepしてヒットしたファイルを、構造を読まずに先例として列挙していた
 - **対策**: ルールの根拠として既存コードを名指しするときは、そのコードがルールの要件（位置・順序・条件）を本当に満たしているかを該当関数を読んで確認する。grepで「同じ識別子を使っている」ことと「同じ規則に従っている」ことは別で、満たさない例を挙げるとルール自体の信頼性を下げる
 - **該当箇所**: .claude/review-lessons.md
+
+### ドキュメント: 入力元が生成しない分岐を根拠に機能を文書化した (PR #233, 2026-10-10)
+- **問題**: `parse_name_status`の`C`（copy）分岐があることを根拠に「copied fileも旧パスと比較する」と書いたが、実際の入力元`diff.get_name_status`は`git diff -M`でrenameしか検出しないため、local modeではcopyが`added`になり分岐に到達しなかった
+- **対策**: パーサーの分岐を根拠に挙動を文書化するときは、呼び出し元のコマンドやAPIがその形式を実際に出力するか（gitのフラグ、APIのstatus値）まで遡って確認する。到達しない分岐はmode限定で書くか、記載から外す
+- **該当箇所**: lua/fude/local/session.lua, doc/fude.txt

README.md

@@ -116,7 +116,7 @@ Not sure which command you need? `:FudeCommandPalette` opens a command palette l
 | `:FudeReviewStart` | Start review session (PR detection, comments, extmarks) |
 | `:FudeReviewStop` | Stop review session |
 | `:FudeReviewToggle` | Toggle review session |
-| `:FudeReviewDiff` | Toggle diff preview window |
+| `:FudeReviewDiff` | Toggle diff preview window (renamed files diff against their old path) |
 | `:FudeReviewComment` | Create pending comment on current line/selection |
 | `:FudeReviewSuggest` | Create pending suggestion on current line/selection |
 | `:FudeReviewViewComment` | View comments on current line (`r` reply, `e` edit, `d` delete, `R` resolve/unresolve the thread) |

doc/fude.txt

@@ -195,6 +195,8 @@ Using lazy.nvim: >lua
     Toggle the diff preview window. Opens a side-by-side diff view
     showing the base branch version of the current file, or closes
     it if already open. Requires an active review session.
+    For a renamed file, the base version is read from its old path,
+    so the diff shows the content changes rather than a new file.
 
 :FudeReviewComment                                  *:FudeReviewComment*
     Create a review comment on the current line (normal mode) or

lua/fude/gh.lua

@@ -113,6 +113,28 @@ function M.get_pr_files(pr_number, callback)
 	}, callback)
 end
 
+--- Convert a files listing from the GitHub API (`pulls/{pr}/files` or
+--- `commits/{sha}`.files) to the changed_files entries used across the plugin.
+--- `previous_path` is set only for renamed/copied files, whose base content
+--- lives under the old name.
+--- @param files table[] API file objects
+--- @return table[] changed files { path, previous_path?, status, additions, deletions, patch }
+function M.build_changed_files(files)
+	local changed = {}
+	for _, f in ipairs(files) do
+		table.insert(changed, {
+			path = f.filename,
+			-- JSON null decodes to vim.NIL, so check the type rather than truthiness
+			previous_path = type(f.previous_filename) == "string" and f.previous_filename or nil,
+			status = f.status,
+			additions = f.additions,
+			deletions = f.deletions,
+			patch = f.patch,
+		})
+	end
+	return changed
+end
+
 --- Get review comments on a PR.
 --- @param pr_number number
 --- @param callback fun(err: string|nil, comments: table|nil)

lua/fude/init.lua

@@ -239,32 +239,14 @@ function M.start()
 		if started_detached and state.original_head_sha then
 			gh_mod.get_commit_files(state.original_head_sha, function(files_err, files)
 				if not files_err and files then
-					state.changed_files = {}
-					for _, f in ipairs(files) do
-						table.insert(state.changed_files, {
-							path = f.filename,
-							status = f.status,
-							additions = f.additions,
-							deletions = f.deletions,
-							patch = f.patch,
-						})
-					end
+					state.changed_files = gh_mod.build_changed_files(files)
 				end
 				on_ready()
 			end)
 		else
 			gh_mod.get_pr_files(state.pr_number, function(files_err, files)
 				if not files_err and files then
-					state.changed_files = {}
-					for _, f in ipairs(files) do
-						table.insert(state.changed_files, {
-							path = f.filename,
-							status = f.status,
-							additions = f.additions,
-							deletions = f.deletions,
-							patch = f.patch,
-						})
-					end
+					state.changed_files = gh_mod.build_changed_files(files)
 				end
 				on_ready()
 			end)
@@ -674,32 +656,14 @@ function M.reload(silent)
 	if config.state.scope == "commit" and config.state.scope_commit_sha then
 		gh_mod.get_commit_files(config.state.scope_commit_sha, function(err, files)
 			if not err and files and config.state == captured_state and config.state.active then
-				config.state.changed_files = {}
-				for _, f in ipairs(files) do
-					table.insert(config.state.changed_files, {
-						path = f.filename,
-						status = f.status,
-						additions = f.additions,
-						deletions = f.deletions,
-						patch = f.patch,
-					})
-				end
+				config.state.changed_files = gh_mod.build_changed_files(files)
 			end
 			on_done()
 		end)
 	else
 		gh_mod.get_pr_files(config.state.pr_number, function(err, files)
 			if not err and files and config.state == captured_state and config.state.active then
-				config.state.changed_files = {}
-				for _, f in ipairs(files) do
-					table.insert(config.state.changed_files, {
-						path = f.filename,
-						status = f.status,
-						additions = f.additions,
-						deletions = f.deletions,
-						patch = f.patch,
-					})
-				end
+				config.state.changed_files = gh_mod.build_changed_files(files)
 			end
 			on_done()
 		end)

lua/fude/local/session.lua

@@ -42,7 +42,7 @@ end
 
 --- Parse `git diff --name-status -M` output.
 --- @param output string|nil
---- @return table[] entries { path, status }
+--- @return table[] entries { path, previous_path?, status }
 function M.parse_name_status(output)
 	local entries = {}
 	if not output or output == "" then
@@ -51,15 +51,16 @@ function M.parse_name_status(output)
 	for line in output:gmatch("[^\n]+") do
 		local letter, rest = line:match("^(%S+)\t(.+)$")
 		if letter and rest then
-			local path = rest
+			local path, previous_path = rest, nil
 			if letter:sub(1, 1) == "R" or letter:sub(1, 1) == "C" then
-				-- "R100\told\tnew" — the review target is the new path
-				local _, new = rest:match("^(.-)\t(.+)$")
+				-- "R100\told\tnew" — the review target is the new path; the old
+				-- one is kept because the base content lives under it
+				local old, new = rest:match("^(.-)\t(.+)$")
 				if new then
-					path = new
+					path, previous_path = new, old
 				end
 			end
-			table.insert(entries, { path = path, status = M.status_word(letter) })
+			table.insert(entries, { path = path, previous_path = previous_path, status = M.status_word(letter) })
 		end
 	end
 	return entries
@@ -101,7 +102,7 @@ end
 --- @param name_status_out string|nil `git diff --name-status -M` output
 --- @param numstat_out string|nil `git diff --numstat -M` output
 --- @param untracked_out string|nil `git ls-files --others --exclude-standard` output
---- @return table[] changed files { path, status, additions, deletions }
+--- @return table[] changed files { path, previous_path?, status, additions, deletions }
 function M.build_changed_files(name_status_out, numstat_out, untracked_out)
 	local counts = M.parse_numstat(numstat_out)
 	local files = {}
@@ -111,6 +112,7 @@ function M.build_changed_files(name_status_out, numstat_out, untracked_out)
 			local c = counts[entry.path] or {}
 			table.insert(files, {
 				path = entry.path,
+				previous_path = entry.previous_path,
 				status = entry.status,
 				additions = c.additions or 0,
 				deletions = c.deletions or 0,

lua/fude/preview.lua

@@ -47,7 +47,16 @@ function M.open_preview(source_win)
 		base_ref = state.scope_commit_sha .. "^"
 	end
 
-	local content, _ = diff.get_base_content(base_ref, rel_path, local_session and local_session.worktree_root or nil)
+	-- Renamed files: the base content lives under the old path. Fall
+	-- back to the new path when the old one is missing at base_ref (the full PR
+	-- scope reads the base branch tip, which may have dropped the old file).
+	local cwd = local_session and local_session.worktree_root or nil
+	local base_path = M.find_base_path(rel_path, state.changed_files)
+	local content, _ = diff.get_base_content(base_ref, base_path, cwd)
+	if not content and base_path ~= rel_path then
+		base_path = rel_path
+		content, _ = diff.get_base_content(base_ref, base_path, cwd)
+	end
 	local source_view = vim.api.nvim_win_call(source_win, vim.fn.winsaveview)
 	local source_foldenable = vim.wo[source_win].foldenable
 	local source_foldlevel = vim.wo[source_win].foldlevel
@@ -86,7 +95,7 @@ function M.open_preview(source_win)
 	vim.wo[preview_win].signcolumn = "no"
 	vim.wo[preview_win].winfixwidth = true
 
-	pcall(vim.api.nvim_buf_set_name, preview_buf, "[base] " .. rel_path)
+	pcall(vim.api.nvim_buf_set_name, preview_buf, "[base] " .. base_path)
 
 	state.preview_win = preview_win
 	state.preview_buf = preview_buf
@@ -138,6 +147,20 @@ function M.open_preview(source_win)
 	opening = false
 end
 
+--- Resolve the path to read the base content from: the old path for a
+--- renamed/copied file, the given path otherwise.
+--- @param rel_path string repo-relative path of the file being viewed
+--- @param changed_files table[]|nil changed files list
+--- @return string
+function M.find_base_path(rel_path, changed_files)
+	for _, f in ipairs(changed_files or {}) do
+		if f.path == rel_path and type(f.previous_path) == "string" and f.previous_path ~= "" then
+			return f.previous_path
+		end
+	end
+	return rel_path
+end
+
 --- Close the preview window and clean up diff mode.
 function M.close_preview()
 	local state = config.state

lua/fude/scope.lua

@@ -634,16 +634,7 @@ function M.apply_full_pr_scope(on_done)
 		state.scope_commit_sha = nil
 		state.scope_commit_index = nil
 		state.gitsigns_reset = false
-		state.changed_files = {}
-		for _, f in ipairs(files) do
-			table.insert(state.changed_files, {
-				path = f.filename,
-				status = f.status,
-				additions = f.additions,
-				deletions = f.deletions,
-				patch = f.patch,
-			})
-		end
+		state.changed_files = gh_mod.build_changed_files(files)
 
 		-- Reset global gitsigns base (clearing commit scope base)
 		-- Then compute merge_base_sha and apply per-buffer base
@@ -747,16 +738,7 @@ function M.apply_commit_scope(sha, on_done)
 		state.scope_commit_sha = sha
 		state.scope_commit_index = M.find_commit_index(state.pr_commits, sha)
 		state.gitsigns_reset = false
-		state.changed_files = {}
-		for _, f in ipairs(files) do
-			table.insert(state.changed_files, {
-				path = f.filename,
-				status = f.status,
-				additions = f.additions,
-				deletions = f.deletions,
-				patch = f.patch,
-			})
-		end
+		state.changed_files = gh_mod.build_changed_files(files)
 
 		-- Update gitsigns base to parent commit
 		local has_gitsigns, gitsigns = pcall(require, "gitsigns")

tests/fude/gh_spec.lua

@@ -100,6 +100,35 @@ describe("parse_viewed_files_response", function()
 	end)
 end)
 
+describe("build_changed_files", function()
+	it("converts API file objects to changed_files entries", function()
+		local files = gh.build_changed_files({
+			{ filename = "lua/a.lua", status = "modified", additions = 3, deletions = 1, patch = "@@ -1 +1 @@" },
+		})
+		assert.same({
+			{ path = "lua/a.lua", status = "modified", additions = 3, deletions = 1, patch = "@@ -1 +1 @@" },
+		}, files)
+	end)
+
+	it("keeps previous_filename of a renamed file as previous_path", function()
+		local files = gh.build_changed_files({
+			{ filename = "lua/new.lua", previous_filename = "lua/old.lua", status = "renamed", additions = 2, deletions = 2 },
+		})
+		assert.equals("lua/new.lua", files[1].path)
+		assert.equals("lua/old.lua", files[1].previous_path)
+		assert.equals("renamed", files[1].status)
+	end)
+
+	it("ignores a JSON null previous_filename", function()
+		local files = gh.build_changed_files({ { filename = "a.lua", previous_filename = vim.NIL, status = "modified" } })
+		assert.is_nil(files[1].previous_path)
+	end)
+
+	it("returns an empty list for no files", function()
+		assert.same({}, gh.build_changed_files({}))
+	end)
+end)
+
 describe("parse_commit_entries", function()
 	it("parses commits with full data", function()
 		local raw = {

tests/fude/local_session_spec.lua

@@ -45,9 +45,14 @@ describe("session.parse_name_status", function()
 		assert.same({ path = "lua/c.lua", status = "removed" }, entries[3])
 	end)
 
-	it("uses the new path for renames", function()
-		local entries = session.parse_name_status("R100\told.lua\tnew.lua\n")
-		assert.same({ path = "new.lua", status = "renamed" }, entries[1])
+	it("uses the new path for renames and keeps the old one", function()
+		local entries = session.parse_name_status("R087\told.lua\tnew.lua\n")
+		assert.same({ path = "new.lua", previous_path = "old.lua", status = "renamed" }, entries[1])
+	end)
+
+	it("keeps the source path for copies", function()
+		local entries = session.parse_name_status("C075\tsrc.lua\tcopy.lua\n")
+		assert.same({ path = "copy.lua", previous_path = "src.lua", status = "copied" }, entries[1])
 	end)
 
 	it("returns empty for nil / empty output", function()
@@ -92,6 +97,18 @@ describe("session.build_changed_files", function()
 		assert.same({ path = "lua/a.lua", status = "modified", additions = 0, deletions = 0 }, files[1])
 	end)
 
+	it("carries the old path of a renamed file", function()
+		local files =
+			session.build_changed_files("R087\tlua/old.lua\tlua/new.lua\n", "4\t2\tlua/{old.lua => new.lua}\n", nil)
+		assert.same({
+			path = "lua/new.lua",
+			previous_path = "lua/old.lua",
+			status = "renamed",
+			additions = 4,
+			deletions = 2,
+		}, files[1])
+	end)
+
 	it("excludes the plugin's own .fude/ store artifacts", function()
 		local files = session.build_changed_files(
 			"M\tlua/a.lua\nA\t.fude/reviews/s1.jsonl\n",

tests/fude/preview_integration_spec.lua

@@ -163,6 +163,43 @@ describe("preview integration", function()
 			assert.is_truthy(content:find("New file", 1, true) or content:find("does not exist", 1, true))
 		end)
 
+		it("reads the base content of a renamed file from its old path", function()
+			local requested = {}
+			helpers.mock(require("fude.diff"), "get_base_content", function(_, path)
+				table.insert(requested, path)
+				if path == "old.lua" then
+					return "old content\n", nil
+				end
+				return nil, "File not found"
+			end)
+			config.state.changed_files = { { path = "source.lua", previous_path = "old.lua", status = "renamed" } }
+
+			open_for_buffer({ "new content" }, "source.lua")
+
+			assert.same({ "old.lua" }, requested)
+			local lines = vim.api.nvim_buf_get_lines(config.state.preview_buf, 0, -1, false)
+			assert.same({ "old content" }, lines)
+			assert.truthy(vim.api.nvim_buf_get_name(config.state.preview_buf):find("[base] old.lua", 1, true))
+		end)
+
+		it("falls back to the new path when the old path is missing at the base", function()
+			local requested = {}
+			helpers.mock(require("fude.diff"), "get_base_content", function(_, path)
+				table.insert(requested, path)
+				if path == "source.lua" then
+					return "same name content\n", nil
+				end
+				return nil, "File not found"
+			end)
+			config.state.changed_files = { { path = "source.lua", previous_path = "old.lua", status = "renamed" } }
+
+			open_for_buffer({ "new content" }, "source.lua")
+
+			assert.same({ "old.lua", "source.lua" }, requested)
+			local lines = vim.api.nvim_buf_get_lines(config.state.preview_buf, 0, -1, false)
+			assert.same({ "same name content" }, lines)
+		end)
+
 		it("records the source buffer the preview was built for", function()
 			local buf = open_for_buffer({ "line 1" }, "source.lua")
 			assert.are.equal(buf, config.state.preview_source_buf)

tests/fude/preview_spec.lua

@@ -59,3 +59,24 @@ describe("is_preview_current", function()
 		assert.is_false(preview.is_preview_current(10, true, 1, nil, 1, 20))
 	end)
 end)
+
+describe("find_base_path", function()
+	it("returns the old path for a renamed file", function()
+		local files = { { path = "lua/new.lua", previous_path = "lua/old.lua", status = "renamed" } }
+		assert.equals("lua/old.lua", preview.find_base_path("lua/new.lua", files))
+	end)
+
+	it("returns the path itself for a file without previous_path", function()
+		local files = { { path = "lua/a.lua", status = "modified" } }
+		assert.equals("lua/a.lua", preview.find_base_path("lua/a.lua", files))
+	end)
+
+	it("returns the path itself for a file outside changed_files", function()
+		local files = { { path = "lua/new.lua", previous_path = "lua/old.lua", status = "renamed" } }
+		assert.equals("lua/other.lua", preview.find_base_path("lua/other.lua", files))
+	end)
+
+	it("handles nil changed_files", function()
+		assert.equals("lua/a.lua", preview.find_base_path("lua/a.lua", nil))
+	end)
+end)