Conditional Shortcut Syntax (#7710)

* Initial Commit

* Update docs

* Add support for elseif blocks

* Another test

* WIP

* Change from `{%if%}` to `<%if%>`

See discussion here - https://talk.tiddlywiki.org/t/proposed-if-widget/7882/64

* Don't use the widget body as the template if a list-empty widget is present

See discussion here - https://github.com/Jermolene/TiddlyWiki5/pull/7710#issuecomment-1717193296

* List widget should search recursively for list-template and list-empty

* Allow block mode content within an if/then/else clause

* Update docs

* Add from-version tag to docs

editions/test/tiddlers/tests/data/conditionals/Basic.tid

@@ -0,0 +1,26 @@
+title: Conditionals/Basic
+description: Basic conditional shortcut syntax
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Text
+
+This is a <% if [<something>match[one]] %>Elephant<% endif %>, I think.
++
+title: Output
+
+<$let something="one">
+{{Text}}
+</$let>
+
+<$let something="two">
+{{Text}}
+</$let>
++
+title: ExpectedResult
+
+<p>
+This is a Elephant, I think.
+</p><p>
+This is a , I think.
+</p>

editions/test/tiddlers/tests/data/conditionals/BlockMode.tid

@@ -0,0 +1,37 @@
+title: Conditionals/BlockMode
+description: Basic conditional shortcut syntax in block mode
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\procedure test(animal)
+<% if [<animal>match[Elephant]] %>
+
+! It is an elephant
+
+<% else %>
+
+<% if [<animal>match[Giraffe]] %>
+
+! It is a giraffe
+
+<% else %>
+
+! It is completely unknown
+
+<% endif %>
+
+<% endif %>
+
+\end
+
+<<test "Giraffe">>
+
+<<test "Elephant">>
+
+<<test "Antelope">>
++
+title: ExpectedResult
+
+<h1 class="">It is a giraffe</h1><h1 class="">It is an elephant</h1><h1 class="">It is completely unknown</h1>

editions/test/tiddlers/tests/data/conditionals/Else.tid

@@ -0,0 +1,26 @@
+title: Conditionals/Else
+description: Else conditional shortcut syntax
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Text
+
+This is a <% if [<something>match[one]] %>Elephant<% else %>Crocodile<% endif %>, I think.
++
+title: Output
+
+<$let something="one">
+{{Text}}
+</$let>
+
+<$let something="two">
+{{Text}}
+</$let>
++
+title: ExpectedResult
+
+<p>
+This is a Elephant, I think.
+</p><p>
+This is a Crocodile, I think.
+</p>

editions/test/tiddlers/tests/data/conditionals/Elseif.tid

@@ -0,0 +1,32 @@
+title: Conditionals/Elseif
+description: Elseif conditional shortcut syntax
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Text
+
+This is a <% if [<something>match[one]] %>Elephant<% elseif [<something>match[two]] %>Antelope<% else %>Crocodile<% endif %>, I think.
++
+title: Output
+
+<$let something="one">
+{{Text}}
+</$let>
+
+<$let something="two">
+{{Text}}
+</$let>
+
+<$let something="three">
+{{Text}}
+</$let>
++
+title: ExpectedResult
+
+<p>
+This is a Elephant, I think.
+</p><p>
+This is a Antelope, I think.
+</p><p>
+This is a Crocodile, I think.
+</p>

editions/test/tiddlers/tests/data/conditionals/MissingEndIf.tid

@@ -0,0 +1,26 @@
+title: Conditionals/MissingEndif
+description: Conditional shortcut syntax with missing endif
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Text
+
+This is a <% if [<something>match[one]] %>Elephant
++
+title: Output
+
+<$let something="one">
+{{Text}}
+</$let>
+
+<$let something="two">
+{{Text}}
+</$let>
++
+title: ExpectedResult
+
+<p>
+This is a Elephant
+</p><p>
+This is a 
+</p>

editions/test/tiddlers/tests/data/conditionals/MultipleResults.tid

@@ -0,0 +1,12 @@
+title: Conditionals/MultipleResults
+description: Check that multiple results from the filter are ignored
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+This is a <% if 1 2 3 4 5 6 %>Elephant<% endif %>, I think.
++
+title: ExpectedResult
+
+<p>This is a Elephant, I think.</p>

editions/test/tiddlers/tests/data/conditionals/Nested.tid

@@ -0,0 +1,38 @@
+title: Conditionals/Nested
+description: Nested conditional shortcut syntax
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\procedure test(animal)
+<% if [<animal>match[Elephant]] %>
+It is an elephant
+<% else %>
+<% if [<animal>match[Giraffe]] %>
+It is a giraffe
+<% else %>
+It is completely unknown
+<% endif %>
+<% endif %>
+\end
+
+<<test "Giraffe">>
+
+<<test "Elephant">>
+
+<<test "Antelope">>
+
++
+title: ExpectedResult
+
+
+
+It is a giraffe
+
+
+It is an elephant
+
+
+It is completely unknown
+

editions/test/tiddlers/tests/data/conditionals/NestedElseif.tid

@@ -0,0 +1,60 @@
+title: Conditionals/NestedElseif
+description: Nested elseif conditional shortcut syntax
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Text
+
+\whitespace trim
+This is a 
+	<% if [<something>match[one]] %>
+		<% if [<another>match[one]] %>
+			Indian
+		<% elseif [<another>match[two]] %>
+			African
+		<% else %>
+			Unknown
+		<% endif %>
+		&#32;Elephant
+	<% elseif [<something>match[two]] %>
+		Antelope
+	<% else %>
+		Crocodile
+	<% endif %>
+, I think.
++
+title: Output
+
+<$let something="one" another="one">
+{{Text}}
+</$let>
+
+<$let something="one" another="two">
+{{Text}}
+</$let>
+
+<$let something="one" another="three">
+{{Text}}
+</$let>
+
+<$let something="two">
+{{Text}}
+</$let>
+
+<$let something="three">
+{{Text}}
+</$let>
++
+title: ExpectedResult
+
+<p>
+This is a Indian Elephant, I think.
+</p><p>
+This is a African Elephant, I think.
+</p><p>
+This is a Unknown Elephant, I think.
+</p><p>
+This is a Antelope, I think.
+</p><p>
+This is a Crocodile, I think.
+</p>