fix: Consider dst when calculating the diff. Fixes #538

Author: kristijanhusak

lua/orgmode/objects/date.lua

@@ -20,6 +20,7 @@ local time_format = '%H:%M'
 ---@field min number
 ---@field timestamp number
 ---@field timestamp_end number
+---@field is_dst boolean
 ---@field is_date_range_start boolean
 ---@field is_date_range_end boolean
 ---@field related_date_range Date
@@ -77,6 +78,7 @@ function Date:new(data)
   opts.timestamp = os.time(opts)
   opts.date_only = date_only
   opts.dayname = os.date('%a', opts.timestamp)
+  opts.is_dst = os.date('*t', opts.timestamp).isdst
   opts.adjustments = data.adjustments or {}
   opts.timestamp_end = data.timestamp_end
   opts.is_date_range_start = data.is_date_range_start or false
@@ -638,11 +640,16 @@ function Date:format(format)
 end
 
 ---@param from Date
----@param span? string
+---@param span? 'day' | 'minute'
 ---@return number
 function Date:diff(from, span)
   span = span or 'day'
-  local diff = self:start_of(span).timestamp - from:start_of(span).timestamp
+  local to_date = self:start_of(span)
+  local from_date = from:start_of(span)
+  local diff = to_date.timestamp - from_date.timestamp
+  if to_date.is_dst ~= from_date.is_dst then
+    diff = diff + (to_date.is_dst and 3600 or -3600)
+  end
   local durations = {
     day = 86400,
     minute = 60,

tests/plenary/object/date_spec.lua

@@ -362,6 +362,26 @@ describe('Date object', function()
     }, dates)
   end)
 
+  it('should return proper diff in days between DST difference', function()
+    -- No overlap
+    local date = Date.from_string('2023-06-26')
+    local end_date = Date.from_string('2023-06-27')
+    assert.are.same(1, end_date:diff(date))
+    assert.are.same(1440, end_date:diff(date, 'minute'))
+
+    -- DST start overlap
+    local date_no_dst = Date.from_string('2023-03-26 Sun')
+    local end_date_dst = Date.from_string('2023-03-27 Mon')
+    assert.are.same(1, end_date_dst:diff(date_no_dst))
+    assert.are.same(1440, end_date_dst:diff(date_no_dst, 'minute'))
+
+    -- DST end overlap
+    local date_dst = Date.from_string('2023-10-28 Sun')
+    local end_date_no_dst = Date.from_string('2023-10-29 Mon')
+    assert.are.same(1, end_date_no_dst:diff(date_dst))
+    assert.are.same(1440, end_date_no_dst:diff(date_dst, 'minute'))
+  end)
+
   it('should format the date', function()
     local date = Date.from_string('2021-05-12 14:00')
     assert.are.same('Wednesday 12 May', date:format('%A %d %B'))
@@ -394,6 +414,7 @@ describe('Date object', function()
       date_only = true,
       day = 15,
       dayname = 'Sat',
+      is_dst = true,
       hour = 0,
       min = 0,
       month = 5,
@@ -425,6 +446,7 @@ describe('Date object', function()
       dayname = 'Sat',
       hour = 0,
       min = 0,
+      is_dst = true,
       month = 5,
       is_date_range_start = false,
       is_date_range_end = false,
@@ -448,6 +470,7 @@ describe('Date object', function()
       hour = 9,
       min = 25,
       month = 6,
+      is_dst = true,
       is_date_range_start = false,
       is_date_range_end = false,
       related_date_range = nil,
@@ -476,6 +499,7 @@ describe('Date object', function()
       dayname = 'Sat',
       hour = 0,
       min = 0,
+      is_dst = true,
       month = 5,
       is_date_range_start = false,
       is_date_range_end = false,
@@ -499,6 +523,7 @@ describe('Date object', function()
       hour = 0,
       min = 0,
       month = 5,
+      is_dst = true,
       is_date_range_start = false,
       is_date_range_end = false,
       related_date_range = nil,
@@ -630,6 +655,7 @@ describe('Date object', function()
       dayname = 'Sat',
       hour = 14,
       min = 30,
+      is_dst = true,
       month = 5,
       is_date_range_start = false,
       is_date_range_end = false,
@@ -654,6 +680,7 @@ describe('Date object', function()
       hour = 0,
       min = 0,
       month = 5,
+      is_dst = true,
       is_date_range_start = false,
       is_date_range_end = false,
       related_date_range = nil,
@@ -681,6 +708,7 @@ describe('Date object', function()
       day = 15,
       dayname = 'Sat',
       hour = 0,
+      is_dst = true,
       min = 0,
       month = 5,
       is_date_range_start = true,
@@ -705,6 +733,7 @@ describe('Date object', function()
       hour = 0,
       min = 0,
       month = 5,
+      is_dst = true,
       is_date_range_start = false,
       is_date_range_end = true,
       related_date_range = dates[1],
@@ -730,6 +759,7 @@ describe('Date object', function()
       is_date_range_start = false,
       is_date_range_end = false,
       related_date_range = nil,
+      is_dst = true,
       range = Range:new({
         start_line = 1,
         end_line = 1,