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

core/modules/parsers/wikiparser/rules/conditional.js

@@ -0,0 +1,120 @@
+/*\
+title: $:/core/modules/parsers/wikiparser/rules/conditional.js
+type: application/javascript
+module-type: wikirule
+
+Conditional shortcut syntax
+
+```
+This is a <% if [{something}] %>Elephant<% elseif [{else}] %>Pelican<% else %>Crocodile<% endif %>
+```
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.name = "conditional";
+exports.types = {inline: true, block: true};
+
+exports.init = function(parser) {
+	this.parser = parser;
+	// Regexp to match
+	this.matchRegExp = /\<\%\s*if\s+/mg;
+	this.terminateIfRegExp = /\%\>/mg;
+};
+
+exports.findNextMatch = function(startPos) {
+	// Look for the next <% if shortcut
+	this.matchRegExp.lastIndex = startPos;
+	this.match = this.matchRegExp.exec(this.parser.source);
+	// If not found then return no match
+	if(!this.match) {
+		return undefined;
+	}
+	// Check for the next %>
+	this.terminateIfRegExp.lastIndex = this.match.index;
+	this.terminateIfMatch = this.terminateIfRegExp.exec(this.parser.source);
+	// If not found then return no match
+	if(!this.terminateIfMatch) {
+		return undefined;
+	}
+	// Return the position at which the construction was found
+	return this.match.index;
+};
+
+/*
+Parse the most recent match
+*/
+exports.parse = function() {
+	// Get the filter condition
+	var filterCondition = this.parser.source.substring(this.match.index + this.match[0].length,this.terminateIfMatch.index);
+	// Advance the parser position to past the %>
+	this.parser.pos = this.terminateIfMatch.index + this.terminateIfMatch[0].length;
+	// Parse the if clause
+	return this.parseIfClause(filterCondition);
+};
+
+exports.parseIfClause = function(filterCondition) {
+	// Create the list widget
+	var listWidget = {
+		type: "list",
+		tag: "$list",
+		isBlock: this.is.block,
+		children: [
+			{
+				type: "list-template",
+				tag: "$list-template"
+			},
+			{
+				type: "list-empty",
+				tag: "$list-empty"
+			}
+		]
+	};
+	$tw.utils.addAttributeToParseTreeNode(listWidget,"filter",filterCondition);
+	$tw.utils.addAttributeToParseTreeNode(listWidget,"variable","condition");
+	$tw.utils.addAttributeToParseTreeNode(listWidget,"limit","1");
+	// Check for an immediately following double linebreak
+	var hasLineBreak = !!$tw.utils.parseTokenRegExp(this.parser.source,this.parser.pos,/([^\S\n\r]*\r?\n(?:[^\S\n\r]*\r?\n|$))/g);
+	// Parse the body looking for else or endif
+	var reEndString = "\\<\\%\\s*(endif)\\s*\\%\\>|\\<\\%\\s*(else)\\s*\\%\\>|\\<\\%\\s*(elseif)\\s+([\\s\\S]+?)\\%\\>",
+		ex;
+	if(hasLineBreak) {
+		ex = this.parser.parseBlocksTerminatedExtended(reEndString);
+	} else {
+		var reEnd = new RegExp(reEndString,"mg");
+		ex = this.parser.parseInlineRunTerminatedExtended(reEnd,{eatTerminator: true});
+	}
+	// Put the body into the list template
+	listWidget.children[0].children = ex.tree;
+	// Check for an else or elseif
+	if(ex.match) {
+		if(ex.match[1] === "endif") {
+			// Nothing to do if we just found an endif
+		} else if(ex.match[2] === "else") {
+			// Check for an immediately following double linebreak
+			hasLineBreak = !!$tw.utils.parseTokenRegExp(this.parser.source,this.parser.pos,/([^\S\n\r]*\r?\n(?:[^\S\n\r]*\r?\n|$))/g);
+			// If we found an else then we need to parse the body looking for the endif
+			var reEndString = "\\<\\%\\s*(endif)\\s*\\%\\>",
+			ex;
+			if(hasLineBreak) {
+				ex = this.parser.parseBlocksTerminatedExtended(reEndString);
+			} else {
+				var reEnd = new RegExp(reEndString,"mg");
+				ex = this.parser.parseInlineRunTerminatedExtended(reEnd,{eatTerminator: true});
+			}
+			// Put the parsed content inside the list empty template
+			listWidget.children[1].children = ex.tree;
+		} else if(ex.match[3] === "elseif") {
+			// Parse the elseif clause by reusing this parser, passing the new filter condition
+			listWidget.children[1].children = this.parseIfClause(ex.match[4]);
+		}
+	}
+	// Return the parse tree node
+	return [listWidget];
+};
+
+})();

core/modules/parsers/wikiparser/wikiparser.js

@@ -223,7 +223,7 @@ Parse a block from the current position
 	terminatorRegExpString: optional regular expression string that identifies the end of plain paragraphs. Must not include capturing parenthesis
 */
 WikiParser.prototype.parseBlock = function(terminatorRegExpString) {
-	var terminatorRegExp = terminatorRegExpString ? new RegExp("(" + terminatorRegExpString + "|\\r?\\n\\r?\\n)","mg") : /(\r?\n\r?\n)/mg;
+	var terminatorRegExp = terminatorRegExpString ? new RegExp(terminatorRegExpString + "|\\r?\\n\\r?\\n","mg") : /(\r?\n\r?\n)/mg;
 	this.skipWhitespace();
 	if(this.pos >= this.sourceLength) {
 		return [];
@@ -264,11 +264,21 @@ WikiParser.prototype.parseBlocksUnterminated = function() {
 };
 
 /*
-Parse blocks of text until a terminating regexp is encountered
+Parse blocks of text until a terminating regexp is encountered. Wrapper for parseBlocksTerminatedExtended that just returns the parse tree
 */
 WikiParser.prototype.parseBlocksTerminated = function(terminatorRegExpString) {
-	var terminatorRegExp = new RegExp("(" + terminatorRegExpString + ")","mg"),
+	var ex = this.parseBlocksTerminatedExtended(terminatorRegExpString);
-		tree = [];
+	return ex.tree;
+};
+
+/*
+Parse blocks of text until a terminating regexp is encountered
+*/
+WikiParser.prototype.parseBlocksTerminatedExtended = function(terminatorRegExpString) {
+	var terminatorRegExp = new RegExp(terminatorRegExpString,"mg"),
+		result = {
+			tree: []
+		};
 	// Skip any whitespace
 	this.skipWhitespace();
 	//  Check if we've got the end marker
@@ -277,7 +287,7 @@ WikiParser.prototype.parseBlocksTerminated = function(terminatorRegExpString) {
 	// Parse the text into blocks
 	while(this.pos < this.sourceLength && !(match && match.index === this.pos)) {
 		var blocks = this.parseBlock(terminatorRegExpString);
-		tree.push.apply(tree,blocks);
+		result.tree.push.apply(result.tree,blocks);
 		// Skip any whitespace
 		this.skipWhitespace();
 		//  Check if we've got the end marker
@@ -286,8 +296,9 @@ WikiParser.prototype.parseBlocksTerminated = function(terminatorRegExpString) {
 	}
 	if(match && match.index === this.pos) {
 		this.pos = match.index + match[0].length;
+		result.match = match;
 	}
-	return tree;
+	return result;
 };
 
 /*
@@ -330,6 +341,11 @@ WikiParser.prototype.parseInlineRunUnterminated = function(options) {
 };
 
 WikiParser.prototype.parseInlineRunTerminated = function(terminatorRegExp,options) {
+	var ex = this.parseInlineRunTerminatedExtended(terminatorRegExp,options);
+	return ex.tree;
+};
+
+WikiParser.prototype.parseInlineRunTerminatedExtended = function(terminatorRegExp,options) {
 	options = options || {};
 	var tree = [];
 	// Find the next occurrence of the terminator
@@ -349,7 +365,10 @@ WikiParser.prototype.parseInlineRunTerminated = function(terminatorRegExp,option
 				if(options.eatTerminator) {
 					this.pos += terminatorMatch[0].length;
 				}
-				return tree;
+				return {
+					match: terminatorMatch,
+					tree: tree
+				};
 			}
 		}
 		// Process any inline rule, along with the text preceding it
@@ -373,7 +392,9 @@ WikiParser.prototype.parseInlineRunTerminated = function(terminatorRegExp,option
 		this.pushTextWidget(tree,this.source.substr(this.pos),this.pos,this.sourceLength);
 	}
 	this.pos = this.sourceLength;
-	return tree;
+	return {
+		tree: tree
+	};
 };
 
 /*

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>

editions/tw5.com/tiddlers/wikitext/Conditional Shortcut Syntax.tid

@@ -0,0 +1,61 @@
+created: 20230901122740573
+modified: 20230901123102263
+tags: WikiText
+title: Conditional Shortcut Syntax
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.3.2">> The conditional shortcut syntax provides a convenient way to express if-then-else logic within WikiText. It evaluates a filter and considers the condition to be true if there is at least one result (regardless of the value of that result).
+
+A simple example:
+
+<$macrocall $name='wikitext-example-without-html'
+src='<% if [{$:/$:/info/url/protocol}match[file:]] %>
+  Loaded from a file URI
+<% else %>
+  Not loaded from a file URI
+<% endif %>
+'/>
+
+One or more `<% elseif %>` clauses may be included before the `<% else %>` clause:
+
+<$macrocall $name='wikitext-example-without-html'
+src='<% if [{$:/$:/info/url/protocol}match[file:]] %>
+  Loaded from a file URI
+<% elseif [{$:/$:/info/url/protocol}match[https:]] %>
+  Loaded from an HTTPS URI
+<% elseif [{$:/$:/info/url/protocol}match[http:]] %>
+  Loaded from an HTTP URI
+<% else %>
+  Loaded from an unknown protocol
+<% endif %>
+'/>
+
+The conditional shortcut syntax can be nested:
+
+<$macrocall $name='wikitext-example-without-html'
+src='\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">>
+'/>
+
+Notes:
+
+* Clauses are parsed in inline mode by default. Force block mode parsing by following the opening `<% if %>`, `<% elseif %>` or `<% else %>` with two line breaks
+* Within an "if" or "elseif" clause, the variable `condition` contains the value of the first result of evaluating the filter condition
+* Widgets and HTML elements must be within a single conditional clause; it is not possible to start an element in one conditional clause and end it in another
+* The conditional shortcut syntax cannot contain pragmas such as procedure definitions
+