getJSDocParameterTags: Always return defined result

src/compiler/checker.ts

@@ -4167,16 +4167,9 @@ namespace ts {
                 return getTypeForBindingElement(<BindingElement>declaration);
             }
 
-            let isOptional = false;
-            if (includeOptionality) {
-                if (isInJavaScriptFile(declaration) && isParameter(declaration)) {
-                    const parameterTags = getJSDocParameterTags(declaration);
-                    isOptional = !!(parameterTags && parameterTags.length > 0 && find(parameterTags, tag => tag.isBracketed));
-                }
-                if (!isBindingElement(declaration) && !isVariableDeclaration(declaration) && !!declaration.questionToken) {
-                    isOptional = true;
-                }
-            }
+            const isOptional = includeOptionality && (
+                isInJavaScriptFile(declaration) && isParameter(declaration) && getJSDocParameterTags(declaration).some(tag => tag.isBracketed)
+                || !isBindingElement(declaration) && !isVariableDeclaration(declaration) && !!declaration.questionToken);
 
             // Use type from type annotation if one is present
             const declaredType = tryGetTypeFromEffectiveTypeNode(declaration);
@@ -6581,23 +6574,10 @@ namespace ts {
         }
 
         function isJSDocOptionalParameter(node: ParameterDeclaration) {
-            if (isInJavaScriptFile(node)) {
-                if (node.type && node.type.kind === SyntaxKind.JSDocOptionalType) {
-                    return true;
-                }
-                const paramTags = getJSDocParameterTags(node);
-                if (paramTags) {
-                    for (const paramTag of paramTags) {
-                        if (paramTag.isBracketed) {
-                            return true;
-                        }
-
-                        if (paramTag.typeExpression) {
-                            return paramTag.typeExpression.type.kind === SyntaxKind.JSDocOptionalType;
-                        }
-                    }
-                }
-            }
+            return isInJavaScriptFile(node) && (
+                node.type && node.type.kind === SyntaxKind.JSDocOptionalType
+                || getJSDocParameterTags(node).some(({ isBracketed, typeExpression }) =>
+                    isBracketed || !!typeExpression && typeExpression.type.kind === SyntaxKind.JSDocOptionalType));
         }
 
         function tryFindAmbientModule(moduleName: string, withAugmentations: boolean) {

src/compiler/utilities.ts

@@ -4419,13 +4419,13 @@ namespace ts {
      * Does not return tags for binding patterns, because JSDoc matches
      * parameters by name and binding patterns do not have a name.
      */
-    export function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag> | undefined {
+    export function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag> {
         if (param.name && isIdentifier(param.name)) {
             const name = param.name.escapedText;
             return getJSDocTags(param.parent).filter((tag): tag is JSDocParameterTag => isJSDocParameterTag(tag) && isIdentifier(tag.name) && tag.name.escapedText === name);
         }
         // a binding pattern doesn't have a name, so it's not possible to match it a JSDoc parameter, which is identified by name
-        return undefined;
+        return emptyArray;
     }
 
     /**
@@ -4481,11 +4481,8 @@ namespace ts {
      */
     export function getJSDocType(node: Node): TypeNode | undefined {
         let tag: JSDocTypeTag | JSDocParameterTag = getFirstJSDocTag(node, SyntaxKind.JSDocTypeTag) as JSDocTypeTag;
-        if (!tag && node.kind === SyntaxKind.Parameter) {
-            const paramTags = getJSDocParameterTags(node as ParameterDeclaration);
-            if (paramTags) {
-                tag = find(paramTags, tag => !!tag.typeExpression);
-            }
+        if (!tag && isParameter(node)) {
+            tag = find(getJSDocParameterTags(node), tag => !!tag.typeExpression);
         }
 
         return tag && tag.typeExpression && tag.typeExpression.type;

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2996,7 +2996,7 @@ declare namespace ts {
      * Does not return tags for binding patterns, because JSDoc matches
      * parameters by name and binding patterns do not have a name.
      */
-    function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag> | undefined;
+    function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag>;
     /**
      * Return true if the node has JSDoc parameter tags.
      *

tests/baselines/reference/api/typescript.d.ts

@@ -3051,7 +3051,7 @@ declare namespace ts {
      * Does not return tags for binding patterns, because JSDoc matches
      * parameters by name and binding patterns do not have a name.
      */
-    function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag> | undefined;
+    function getJSDocParameterTags(param: ParameterDeclaration): ReadonlyArray<JSDocParameterTag>;
     /**
      * Return true if the node has JSDoc parameter tags.
      *