Merge 91b274c into 8dfe3c3

documentation/c05-packages.sil

@@ -274,6 +274,10 @@ This section introduces packages that could not fit in another category.
 \status:low
 \package-documentation{ifattop}
 
+\subsection{defaults}
+\status:high
+\package-documentation{defaults}
+
 \section{Frames and page layouts}
 
 As we mentioned in the first chapter, SILE uses frames as an indication of where to put text onto

packages/defaults/init.lua

@@ -0,0 +1,75 @@
+local base = require("packages.base")
+
+local package = pl.class(base)
+package._name = "defaults"
+
+local semver = require("semver")
+
+local semver_descending = function (a, b)
+   a, b = semver(a), semver(b)
+   return a > b
+end
+
+-- Defaults that go out of fassion
+package.old_defaults = {
+   ["0.15.0"] = {
+      ["shaper.spaceenlargementfactor"] = 1.2,
+      ["document.parindent"] = SILE.nodefactory.glue(20),
+      -- ["linespacing.method"] = "tex",
+   },
+}
+
+function package:_init (options)
+  base._init(self, options)
+  self:defaults(options.target)
+end
+
+function package:defaults (target)
+  target = semver(target and target or SILE.version)
+  local target_hit = false
+  for version, settings in pl.tablex.sort(self.old_defaults, semver_descending) do
+     version = semver(version)
+     for parameter, value in pairs(settings) do
+        SU.debug("defaults", ("Resetting '%s' to '%s' as it was prior to v%s"):format(parameter, tostring(value), version))
+        SILE.settings:set(parameter, value, true)
+     end
+     if target_hit then break end
+     if version <= target then target_hit = true end
+  end
+end
+
+function package:registerCommands ()
+
+  self:registerCommand("defaults", function (options, content)
+     if content then
+        SILE.settings:temporarily(function ()
+           self:defaults(options.target)
+        end)
+     else
+        self:defaults(options.target)
+     end
+  end)
+
+end
+
+local doctarget = "v" .. tostring(semver(SILE.version))
+package.documentation = ([[
+\begin{document}
+
+From time to time, the default value of a setting in SILE might change with a new release.
+If these changes are expected to cause document reflows they will be marked as breaking changes.
+The previous behaviour can always be restored by manually setting the old values, but knowing what those are requires carefully reading the release notes.
+This package tries to restore as many previous setting values as possible to make old document render like they would have in previous releases without changing the documents themselves (beyond loading this package).
+
+From inside a document, use \autodoc:command{\use[module=packages.defaults,target=%s]} to set defaults as they would have been in SILE %s.
+
+This can also be triggered from the command line with no changes to a document:
+
+\begin{autodoc:codeblock}
+$ sile -u 'packages.defaults[target=%s]'
+\end{autodoc:codeblock}
+
+\end{document}
+]]):format(doctarget, doctarget, doctarget)
+
+return package