Improve error messaging for incorrect XML tag casing

src/DiagnosticMessages.ts

@@ -354,6 +354,11 @@ export let DiagnosticMessages = {
         code: 1065,
         severity: DiagnosticSeverity.Error
     }),
+    xmlTagCaseMismatch: (tagName: string, expectedTagName: string) => ({
+        message: `Tag '${tagName}' must be all lower case. Use '${expectedTagName}' instead.`,
+        code: 1143,
+        severity: DiagnosticSeverity.Error
+    }),
     expectedStatementOrFunctionCallButReceivedExpression: () => ({
         message: `Expected statement or function call but instead found expression`,
         code: 1066,

src/parser/SGParser.spec.ts

@@ -113,6 +113,58 @@ describe('SGParser', () => {
         });
     });
 
+    it('Adds error when incorrect casing is used for children tag', () => {
+        const parser = new SGParser();
+        parser.parse(
+            'pkg:/components/ParentScene.xml', trim`
+            <?xml version="1.0" encoding="utf-8" ?>
+            <component name="ChildScene" extends="ParentScene">
+                <Children>
+                    <Label id="test" />
+                </Children>
+            </component>
+        `);
+        expect(parser.diagnostics).to.be.lengthOf(1);
+        expect(parser.diagnostics[0]).to.deep.include({
+            ...DiagnosticMessages.xmlTagCaseMismatch('Children', 'children'),
+            range: Range.create(2, 5, 2, 13)
+        });
+    });
+
+    it('Adds error when incorrect casing is used for interface tag', () => {
+        const parser = new SGParser();
+        parser.parse(
+            'pkg:/components/ParentScene.xml', trim`
+            <?xml version="1.0" encoding="utf-8" ?>
+            <component name="ChildScene" extends="ParentScene">
+                <Interface>
+                    <field id="test" type="string" />
+                </Interface>
+            </component>
+        `);
+        expect(parser.diagnostics).to.be.lengthOf(1);
+        expect(parser.diagnostics[0]).to.deep.include({
+            ...DiagnosticMessages.xmlTagCaseMismatch('Interface', 'interface'),
+            range: Range.create(2, 5, 2, 14)
+        });
+    });
+
+    it('Adds error when incorrect casing is used for script tag', () => {
+        const parser = new SGParser();
+        parser.parse(
+            'pkg:/components/ParentScene.xml', trim`
+            <?xml version="1.0" encoding="utf-8" ?>
+            <component name="ChildScene" extends="ParentScene">
+                <Script type="text/brightscript" uri="./test.brs" />
+            </component>
+        `);
+        expect(parser.diagnostics).to.be.lengthOf(1);
+        expect(parser.diagnostics[0]).to.deep.include({
+            ...DiagnosticMessages.xmlTagCaseMismatch('Script', 'script'),
+            range: Range.create(2, 5, 2, 11)
+        });
+    });
+
     it('Adds error when a leaf tag is found to have children', () => {
         const parser = new SGParser();
         parser.parse(

src/parser/SGParser.ts

@@ -257,11 +257,23 @@ function mapElements(content: ContentCstNode, allow: string[], diagnostics: Diag
                 if (allow.includes(name.image)) {
                     tags.push(mapElement(entry, diagnostics));
                 } else {
-                    //unexpected tag
-                    diagnostics.push({
-                        ...DiagnosticMessages.xmlUnexpectedTag(name.image),
-                        range: rangeFromTokens(name)
-                    });
+                    // Check if this is a case mismatch for a known tag
+                    const lowerCaseTag = name.image.toLowerCase();
+                    const matchingAllowedTag = allow.find(allowedTag => allowedTag.toLowerCase() === lowerCaseTag);
+
+                    if (matchingAllowedTag && matchingAllowedTag !== name.image) {
+                        // Case mismatch for a known tag
+                        diagnostics.push({
+                            ...DiagnosticMessages.xmlTagCaseMismatch(name.image, matchingAllowedTag),
+                            range: rangeFromTokens(name)
+                        });
+                    } else {
+                        // Truly unexpected tag
+                        diagnostics.push({
+                            ...DiagnosticMessages.xmlUnexpectedTag(name.image),
+                            range: rangeFromTokens(name)
+                        });
+                    }
                 }
             } else {
                 //bad xml syntax...