Fix dealiaser throwing on TypeAlias nodes.

getAliasedSymbol only accepts Alias, not TypeAlias, so filter on that only.

PiperOrigin-RevId: 264161077

internal/tsetse/tests/ban_conformance_pattern/name_test.ts

diff --git a/internal/tsetse/tests/ban_conformance_pattern/name_test.ts b/internal/tsetse/tests/ban_conformance_pattern/name_test.ts
index 6bb06ec..d3ffdd0 100644
--- a/internal/tsetse/tests/ban_conformance_pattern/name_test.ts
+++ b/internal/tsetse/tests/ban_conformance_pattern/name_test.ts
@@ -38,6 +38,30 @@
       messageText: 'no blob url'
     });
   });
+
+  it('does not choke on type aliases', () => {
+    // This test case checks that we do not regress on the AbsoluteMatcher's
+    // handling of type aliases. In dealias, from utils/ast_tools.ts, the
+    // typechecker's getAliasedSymbol function should only be called with
+    // Symbols that verify ts.SymbolFlags.Alias, and ts.SymbolFlags.TypeAlias is
+    // not acceptable (the typechecker will throw).
+
+    const sources = [
+      `export type Foo = {bar: number, baz: (x:string)=>void}`,
+      `import {Foo} from './file_0';
+       export const c: Foo["baz"] = (x:string)=>{};`,
+      `import {c} from './file_1'; c(window.name);`
+    ];
+    const results = compileAndCheck(
+        new ConformancePatternRule({
+          errorMessage: 'should not trigger',
+          kind: PatternKind.BANNED_NAME,
+          values: ['whatever']
+        }),
+        ...sources);
+
+    expect(results.length).toBe(0);
+  });
 });
 
 beforeEach(() => {

internal/tsetse/util/ast_tools.ts

diff --git a/internal/tsetse/util/ast_tools.ts b/internal/tsetse/util/ast_tools.ts
index cb0f0cb..024c008 100644
--- a/internal/tsetse/util/ast_tools.ts
+++ b/internal/tsetse/util/ast_tools.ts
@@ -100,7 +100,8 @@
   if (!symbol) {
     return undefined;
   }
-  if (symbol.getFlags() & (ts.SymbolFlags.Alias | ts.SymbolFlags.TypeAlias)) {
+  if (symbol.getFlags() & ts.SymbolFlags.Alias) {
+    // Note: something that has only TypeAlias is not acceptable here.
     return dealias(tc.getAliasedSymbol(symbol), tc);
   }
   return symbol;