[wasm] Use "wasm-function[i]" for wasm function name

BUG=chromium:863205
R=clemensh@chromium.org

Change-Id: I15f3a09e15210a80b155def5761d9aead95d19b7
Reviewed-on: https://chromium-review.googlesource.com/1156386Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54811}

src/wasm/wasm-objects.cc

@@ -675,7 +675,11 @@ Handle<String> WasmModuleObject::GetFunctionName(
   MaybeHandle<String> name =
       GetFunctionNameOrNull(isolate, module_object, func_index);
   if (!name.is_null()) return name.ToHandleChecked();
-  return isolate->factory()->NewStringFromStaticChars("<WASM UNNAMED>");
+  EmbeddedVector<char, 32> buffer;
+  int length = SNPrintF(buffer, "wasm-function[%u]", func_index);
+  return isolate->factory()
+      ->NewStringFromOneByte(Vector<uint8_t>::cast(buffer.SubVector(0, length)))
+      .ToHandleChecked();
 }
 
 Vector<const uint8_t> WasmModuleObject::GetRawFunctionName(

src/wasm/wasm-objects.h

@@ -174,8 +174,8 @@ class WasmModuleObject : public JSObject {
                                                    uint32_t func_index);
 
   // Get the function name of the function identified by the given index.
-  // Returns "<WASM UNNAMED>" if the function is unnamed or the name is not a
-  // valid UTF-8 string.
+  // Returns "wasm-function[func_index]" if the function is unnamed or the
+  // name is not a valid UTF-8 string.
   static Handle<String> GetFunctionName(Isolate*, Handle<WasmModuleObject>,
                                         uint32_t func_index);
 

test/mjsunit/wasm/function-names.js

@@ -40,7 +40,7 @@ var module = builder.instantiate();
     for (var i = 0; i < names.length; ++i) {
       var line = lines[i].trim();
       if (names[i] === null) continue;
-      var printed_name = names[i] === undefined ? "<WASM UNNAMED>" : names[i]
+      var printed_name = names[i];
       var expected_start = "at " + printed_name + " (";
       assertTrue(line.startsWith(expected_start),
           "should start with '" + expected_start + "': '" + line + "'");