Allow dotted names in templates to select into sub-objects.

Part of #50.

README.md

@@ -771,6 +771,8 @@ thrown. Variables named `_` will have their results ignored.
 
 Template names can also have modifiers: `My name is {{name|default:'Alex'}}` would mean that if the var `name` is not provided, it will return `Alex`. Some modifiers expect arguments and some don't. If it expects a string argument, it should be wrapped in either `'` or `"`. You can chain multiple, e.g. `{{name|default:'Alex'|optional}}`.
 
+Template names can also have a `.` in them, which selects into the sub object. For example, `My name is {{person.name}}`, given `{person:{name:'Alex'}}` would render `My name is Alex`.
+
 Modifiers:
 - `default:'value'` - if the var isn't provided, it will use the provided value. Must always be provided as a string value. It will be coerced into a different type if one of the type modifiers is used.
 - `optional` (expects no arguments) - for template.extract, the pattern doesn't need to exist. If it doesn't, it will return the default value or skip the key if no default has been configured. Ignored for template.render().

src/template.ts

@@ -3,7 +3,7 @@ import {
 } from 'zod';
 
 import {
-	assertUnreachable
+	assertUnreachable, getObjectProperty, setObjectProperty
 } from './util.js';
 
 //Unknown is a stand-in for JSON-style output
@@ -13,7 +13,7 @@ type TemplateValueArray = TemplateVars[];
 
 type TemplateValue = TemplateValueArray | TemplateValueLeaf;
 
-const templateVarRegExp = new RegExp('^[a-zA-Z0-9-_]+$');
+const templateVarRegExp = new RegExp('^[a-zA-Z0-9-_.]+$');
 
 const templateVar = z.string().regex(templateVarRegExp);
 
@@ -369,7 +369,7 @@ const renderTemplatePiece = (piece : TemplatePart, vars : TemplateVars) : string
 	if (typeof piece == 'string') return piece;
 	if (piece.var == IGNORE_VAR) return '';
 	//It's a replacement.
-	const v = vars[piece.var];
+	const v = getObjectProperty(vars, piece.var);
 	if (v === undefined) {
 		if (piece.default === undefined) throw new Error(`Template had a placeholder for ${piece.var} but it did not exist in vars and no default was provided.`);
 		return piece.default;
@@ -399,7 +399,7 @@ const defaultForPieces = (pieces : TemplatePart[]) : TemplateVars => {
 		//in later.
 		if (piece.default == undefined) continue;
 		const converter = VALUE_EXTRACTORS[piece.type];
-		result[piece.var] = converter(piece.default);
+		setObjectProperty(result, piece.var, converter(piece.default));
 	}
 	return result;
 };
@@ -459,7 +459,7 @@ const _extractForTemplate = (input : string, pieces : TemplatePart[], loop : boo
 			if (match == undefined || match == '') continue;
 			//If it's '_' then we're told to drop it on the floor.
 			if (v.var == IGNORE_VAR) continue;
-			result[v.var] = extractForPiece(match, v);
+			setObjectProperty(result, v.var, extractForPiece(match, v));
 		}
 		results.push(result);
 	}

test/template/test.ts

@@ -379,6 +379,36 @@ describe('Template', () => {
 		assert.deepStrictEqual(actual, golden);
 	});
 
+	it('template that uses a dotted property name', () => {
+		const template = 'foo{{ a.b|int}}';
+		const input = {
+			a: {
+				b: 3
+			}
+		};
+		const t = new Template(template);
+		const actual = t.render(input);
+		const golden = 'foo3';
+		assert.deepStrictEqual(actual, golden);
+	});
+
+	it('template with a loop that uses a dotted property name', () => {
+		const template = '{{ @loop:bar}}foo{{ a.b|int}}{{@end}}';
+		const input = {
+			bar: [
+				{
+					a: {
+						b: 3
+					}
+				}
+			]
+		};
+		const t = new Template(template);
+		const actual = t.render(input);
+		const golden = 'foo3';
+		assert.deepStrictEqual(actual, golden);
+	});
+
 });
 
 describe('template.extract', () => {
@@ -629,6 +659,49 @@ describe('template.extract', () => {
 		assert.deepStrictEqual(actual, golden);
 	});
 
+	it('dotted property extract works', () => {
+		const template = 'foo{{ a.b|int}}';
+		const input = 'foo342';
+		const t = new Template(template);
+		const actual = t.extract(input);
+		const golden = {
+			a: {
+				b: 342
+			}
+		};
+		assert.deepStrictEqual(actual, golden);
+	});
+
+	it('dotted property extract works', () => {
+		const template = '{{ @loop:bar}}foo{{ a.b|int}}{{%end}}';
+		const input = 'foo342';
+		const t = new Template(template);
+		const actual = t.extract(input);
+		const golden = {
+			bar: [
+				{
+					a: {
+						b: 342
+					}
+				}
+			]
+		};
+		assert.deepStrictEqual(actual, golden);
+	});
+
+	it('dotted property with default extract works', () => {
+		const template = 'foo{{ a.b|default:"342"}}';
+		const input = 'foo';
+		const t = new Template(template);
+		const actual = t.extract(input);
+		const golden = {
+			a: {
+				b: '342'
+			}
+		};
+		assert.deepStrictEqual(actual, golden);
+	});
+
 	it('pattern modifier', () => {
 		const template = 'foo{{name|pattern:"\\d+?"}}';
 		const input = 'foo342';