Fix Function.end_token_pos() and implement MethodMirror.source getter

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index ed78b7bbfe150d5073e390c1a46cc88800bbbff1..bafb2ea95300c64a00bdd97ba885710a302e289a 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1292,6 +1292,35 @@ DEFINE_NATIVE_ENTRY(MethodMirror_return_type, 1) {
 }
 
 
+DEFINE_NATIVE_ENTRY(MethodMirror_source, 1) {
+  GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
+  const Function& func = Function::Handle(ref.GetFunctionReferent());
+  const Script& script = Script::Handle(func.script());
+  const TokenStream& stream = TokenStream::Handle(script.tokens());
+  const TokenStream::Iterator tkit(stream, func.end_token_pos());
+  intptr_t from_line;
+  intptr_t from_col;
+  intptr_t to_line;
+  intptr_t to_col;
+  script.GetTokenLocation(func.token_pos(), &from_line, &from_col);
+  script.GetTokenLocation(func.end_token_pos(), &to_line, &to_col);
+  intptr_t last_tok_len = String::Handle(tkit.CurrentLiteral()).Length();
+  // Handle special cases for end tokens of closures (where we exclude the last
+  // token):
+  // (1) "foo(() => null, bar);": End token is `,', but we don't print it.
+  // (2) "foo(() => null);": End token is ')`, but we don't print it.
+  // (3) "var foo = () => null;": End token is `;', but in this case the token
+  // semicolon belongs to the assignment so we skip it.
+  if ((tkit.CurrentTokenKind() == Token::kCOMMA) ||                   // Case 1.
+      (tkit.CurrentTokenKind() == Token::kRPAREN) ||                  // Case 2.
+      (tkit.CurrentTokenKind() == Token::kSEMICOLON &&
+       String::Handle(func.name()).Equals("<anonymous closure>"))) {  // Case 3.
+    last_tok_len = 0;
+  }
+  return script.GetSnippet(from_line, from_col, to_line, to_col + last_tok_len);
+}
+
+
 DEFINE_NATIVE_ENTRY(TypedefMirror_referent, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Class& cls = Class::Handle(ref.GetClassReferent());