[tsgen] Error out when using --emit-tsd with wasm only output. (#21742)

Fixes #21740

Author: brendandahl

test/test_other.py

@@ -3307,6 +3307,11 @@ def test_emit_tsd(self):
     cmd = shared.get_npm_cmd('tsc') + [test_file('other/test_tsd.ts'), '--noEmit']
     shared.check_call(cmd)
 
+  def test_emit_tsd_wasm_only(self):
+    err = self.expect_fail([EMCC, test_file('other/test_emit_tsd.c'),
+                            '--emit-tsd', 'test_emit_tsd_wasm_only.d.ts', '-o', 'out.wasm'])
+    self.assertContained('Wasm only output is not compatible --emit-tsd', err)
+
   def test_emconfig(self):
     output = self.run_process([emconfig, 'LLVM_ROOT'], stdout=PIPE).stdout.strip()
     self.assertEqual(output, config.LLVM_ROOT)

tools/link.py

@@ -787,6 +787,8 @@ def phase_linker_setup(options, state, newargs):
     settings.MODULARIZE = 1
 
   if options.oformat in (OFormat.WASM, OFormat.BARE):
+    if options.emit_tsd:
+      exit_with_error('Wasm only output is not compatible --emit-tsd')
     # If the user asks directly for a wasm file then this *is* the target
     wasm_target = target
   elif settings.SINGLE_FILE or settings.WASM == 0: