Use reproducible timestamp during build

During build svg images of the calendar widget are generated, which
differ based on the current date.
By honouring the environment variable SOURCE_DATE_EPOCH, which is
set by distributions during build, a deterministic date can be used
at build time while keeping the normal behaviour during runtime.

See also: https://reproducible-builds.org/specs/source-date-epoch/

tests/examples/shims/_date.lua

@@ -0,0 +1,11 @@
+local source_date_epoch = os.getenv("SOURCE_DATE_EPOCH")
+if source_date_epoch then
+    local old_osdate = os.date
+    os.date = function(format, timestamp) -- luacheck: ignore
+        if timestamp then
+            return old_osdate(format, timestamp)
+        end
+        format = "!" .. format
+        return old_osdate(format, source_date_epoch)
+    end
+end

tests/examples/wibox/widget/calendar/fn_embed_cell.lua

@@ -3,6 +3,7 @@ local wibox     = require("wibox") --DOC_HIDE
 local gears     = require("gears") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/calendar/font.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("sans 12") --DOC_HIDE

tests/examples/wibox/widget/calendar/long_weekdays.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/calendar/month.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE_ALL
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/calendar/start_sunday.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/calendar/week_numbers.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/calendar/year.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE

tests/examples/wibox/widget/defaults/calendar.lua

@@ -2,6 +2,7 @@ local parent    = ... --DOC_HIDE
 local wibox     = require("wibox") --DOC_HIDE
 local beautiful = require( "beautiful" ) --DOC_HIDE
 local Pango     = require("lgi").Pango --DOC_HIDE
+require("_date") --DOC_HIDE
 
 -- Beautiful fake get_font --DOC_HIDE
 local f = Pango.FontDescription.from_string("monospace 10") --DOC_HIDE