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fix(compact): align zero-width hunk context #512

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6d4654e
fix(compact): align zero-width hunk context
caenrique Aug 2, 2026
053c99c
pr-feedback: remove comment not longer relevant
caenrique Aug 3, 2026
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23 changes: 13 additions & 10 deletions lua/codediff/ui/view/compact.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -79,11 +79,6 @@ function M.compute_visible_lines(changes, side, line_count, context_lines)
local range_start = range.start_line
local range_end = range.end_line -- exclusive

-- For zero-width ranges (pure insertion/deletion), use start_line as anchor
if range_start == range_end then
range_end = range_start + 1
end

local ctx_start = math.max(1, range_start - context_lines)
local ctx_end = math.min(line_count, range_end - 1 + context_lines)
for l = ctx_start, ctx_end do
Expand All @@ -98,7 +93,17 @@ end
-- closes folds — navigation keys like zj/zk/]z/[z are excluded since they
-- don't change fold state).
local FOLD_KEYS = {
"zo", "zO", "zc", "zC", "za", "zA", "zv", "zx", "zX", "zM", "zR",
"zo",
"zO",
"zc",
"zC",
"za",
"zA",
"zv",
"zx",
"zX",
"zM",
"zR",
}

--- Install buffer-local keymap wraps that propagate fold-open/close actions
Expand Down Expand Up @@ -126,8 +131,7 @@ local function setup_fold_sync(session, tabpage)
lifecycle.begin_keymap_scope(tabpage, "compact")

for _, pane in ipairs(panes) do
if pane.win and vim.api.nvim_win_is_valid(pane.win)
and pane.buf and vim.api.nvim_buf_is_valid(pane.buf) then
if pane.win and vim.api.nvim_win_is_valid(pane.win) and pane.buf and vim.api.nvim_buf_is_valid(pane.buf) then
for _, key in ipairs(FOLD_KEYS) do
lifecycle.set_buf_keymap(tabpage, pane.buf, "n", key, function()
local count = vim.v.count > 0 and tostring(vim.v.count) or ""
Expand All @@ -153,8 +157,7 @@ local function setup_fold_sync(session, tabpage)
_syncing = true
local ok, err = pcall(function()
for _, other in ipairs(panes) do
if other.win ~= pane.win
and other.win and vim.api.nvim_win_is_valid(other.win) then
if other.win ~= pane.win and other.win and vim.api.nvim_win_is_valid(other.win) then
local target = M.compute_corresponding_lnum(changes, pane.side, other.side, src_lnum)
target = math.max(1, math.min(target, vim.api.nvim_buf_line_count(other.buf)))
-- Save & restore cursor so the partner pane doesn't visibly jump.
Expand Down
26 changes: 21 additions & 5 deletions tests/ui/view/compact_spec.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -125,16 +125,16 @@ describe("compact mode (#344)", function()
assert.is_nil(visible[11], "buffer only has 10 lines")
end)

it("treats zero-width ranges (pure insertion/deletion) as a one-line anchor", function()
-- Zero-width range at line 5 — gets treated as the one-line slice [5,6).
-- With context=2: visible = max(1, 5-2)..min(N, 6-1+2) = 3..7.
it("shows context on both sides of zero-width ranges without an extra anchor line", function()
-- A zero-width range is a boundary between lines, not a changed line.
-- With context=2, show two real lines on either side: 3..6.
local changes = { make_change(5, 5, 5, 8) }
local visible = compact.compute_visible_lines(changes, "original", 100, 2)
for l = 3, 7 do
for l = 3, 6 do
assert.is_true(visible[l], "line " .. l .. " should be visible")
end
assert.is_nil(visible[2])
assert.is_nil(visible[8])
assert.is_nil(visible[7])
end)

it("merges overlapping hunks' visible ranges via set union", function()
Expand Down Expand Up @@ -162,6 +162,8 @@ describe("compact mode (#344)", function()
-- Original side: anchor at 5, ±2 context → 3..6.
assert.is_true(orig_visible[5])
assert.is_true(orig_visible[3])
assert.is_true(orig_visible[6])
assert.is_nil(orig_visible[7])
assert.is_nil(orig_visible[10])

-- Modified side: hunk 10..12, ±2 context → 8..14.
Expand All @@ -170,6 +172,20 @@ describe("compact mode (#344)", function()
assert.is_nil(mod_visible[5])
end)

it("aligns the first folded line after a pure insertion", function()
local changes = { make_change(50, 50, 60, 61) }
local original = compact.compute_visible_lines(changes, "original", 100, 3)
local modified = compact.compute_visible_lines(changes, "modified", 110, 3)

-- Context ends at 52/63, so the next folds begin at corresponding
-- unchanged lines 53/64. Before the fix, the original fold began at 54.
assert.is_true(original[52])
assert.is_true(modified[63])
assert.is_nil(original[53])
assert.is_nil(modified[64])
assert.equal(64, compact.compute_corresponding_lnum(changes, "original", "modified", 53))
end)

it("supports zero context (only the hunk lines visible)", function()
local changes = { make_change(10, 13, 10, 13) }
local visible = compact.compute_visible_lines(changes, "original", 100, 0)
Expand Down