refactor(tsUtils): move logic for looking up method type definition

projects/igniteui-angular/migrations/common/tsUtils.ts

@@ -261,24 +261,9 @@ export const getTypeDefinitionAtPosition =
             return langServ.getDefinitionAndBoundSpan(entryPath, definition.textSpan.start).definitions[0];
         }
         if (definition.kind.toString() === 'method') {
-            /** TODO: use typechecker for all the things? */
-            const typeChecker = langServ.getProgram().getTypeChecker();
-            const sourceFile = langServ.getProgram().getSourceFile(definition.fileName);
-
-            const classDeclaration = sourceFile.statements
-                .filter((m): m is tss.ClassDeclaration => m.kind === tss.SyntaxKind.ClassDeclaration)
-                .find(m => m.name && m.name.getText() === definition.containerName);
-
-            const node = classDeclaration.members
-                .filter((m): m is tss.MethodDeclaration => m.kind === tss.SyntaxKind.MethodDeclaration)
-                .find(m => m.name.getText() === definition.name);
-
-            const returnType = typeChecker.getReturnTypeOfSignature(typeChecker.getSignatureFromDeclaration(node));
-            const name = returnType.symbol.escapedName.toString();
-            const fileName = returnType.symbol.declarations[0].getSourceFile().fileName;
-
-            return { name, fileName };
+            return getMethodTypeDefinition(langServ, definition);
         }
+
         let typeDefs = getTypeDefinitions(langServ, definition.fileName || entryPath, definition.textSpan.start);
         // if there are no type definitions found, the identifier is a ts property, referred in an internal/external template
         // or is a reference in a decorator
@@ -300,9 +285,11 @@ export const getTypeDefinitionAtPosition =
                 return null;
             }
 
+            // find the class declaration in the source file where the member that we want to migrate is declared
+            // atm we are explicitly ignoring unnamed class declarations like - export default class { ... }
             const classDeclaration = sourceFile.statements
                 .filter((m): m is tss.ClassDeclaration => m.kind === tss.SyntaxKind.ClassDeclaration)
-                .find(m => m.name && m.name.getText() === definition.containerName);
+                .find(m => m.name?.getText() === definition.containerName);
 
             if (!classDeclaration) {
                 // there must be at least one class declaration in the .ts file and the property must belong to it
@@ -358,10 +345,51 @@ export const isMemberIgniteUI =
 const shiftMatchPosition = (matchPosition: number, content: string): number => {
     do {
         matchPosition--;
-    } while (matchPosition > 0
-    && !content[matchPosition - 1].trim()
+    } while (matchPosition > 0 && !content[matchPosition - 1].trim()
         || content[matchPosition - 1] === SynaxTokens.MemberAccess);
     return matchPosition;
 };
 
+/**
+ * Looks up a method's definition return type.
+ *
+ * @param langServ The TypeScript LanguageService.
+ * @param definition The method definition.
+ */
+const getMethodTypeDefinition = (langServ: tss.LanguageService, definition: tss.DefinitionInfo):
+    Pick<tss.DefinitionInfo, 'name' | 'fileName'> | null => {
+    // TODO: use typechecker for all the things?
+    const sourceFile = langServ.getProgram().getSourceFile(definition.fileName);
+
+    // find the class declaration in the source file where the method that we want to migrate is declared
+    const classDeclaration = sourceFile.statements
+        .filter((m): m is tss.ClassDeclaration => m.kind === tss.SyntaxKind.ClassDeclaration)
+        .find(m => m.name?.getText() === definition.containerName);
+
+    // find the node in the class declaration's members which represents the method
+    const methodDeclaration = classDeclaration?.members
+        .filter((m): m is tss.MethodDeclaration => m.kind === tss.SyntaxKind.MethodDeclaration)
+        .find(m => m.name.getText() === definition.name);
+
+    if (!methodDeclaration) {
+        return null;
+    }
+
+    // use the TypeChecker to resolve implicit/explicit method return types
+    const typeChecker = langServ.getProgram().getTypeChecker();
+    const signature = typeChecker.getSignatureFromDeclaration(methodDeclaration);
+    if (!signature) {
+        return null;
+    }
+    const returnType = typeChecker.getReturnTypeOfSignature(signature);
+    const name = returnType.symbol.escapedName.toString();
+    if (returnType.symbol.declarations?.length > 0) {
+        // there should never be a case where a type is declared in more than one file
+        const fileName = returnType.symbol.declarations[0].getSourceFile().fileName;
+        return { name, fileName };
+    }
+
+    return null;
+};
+
 //#endregion