Discard first line of multiline string if only whitespace

runtime/vm/scanner.cc

Index: runtime/vm/scanner.cc
===================================================================
--- runtime/vm/scanner.cc	(revision 27888)
+++ runtime/vm/scanner.cc	(working copy)
@@ -422,19 +422,14 @@
 
   // Entering string scanning mode.
   BeginStringLiteral(c0_);
-  string_is_multiline_ = (LookaheadChar(1) == c0_) &&
-      (LookaheadChar(2) == c0_);
+  ReadChar();
 
-  ReadChar();  // Skip opening delimiter.
-  if (string_is_multiline_) {
+  if ((c0_ == string_delimiter_) && (LookaheadChar(1) == string_delimiter_)) {
+    string_is_multiline_ = true;
     ReadChar();  // Skip two additional string delimiters.
     ReadChar();
-    if (c0_ == '\n') {
-      // Skip first character of multiline string if it is a newline.
-      ReadChar();
-    }
   }
-  ScanLiteralStringChars(is_raw);
+  ScanLiteralStringChars(is_raw, string_is_multiline_);
 }
 
 
@@ -497,7 +492,7 @@
 }
 
 
-void Scanner::ScanLiteralStringChars(bool is_raw) {
+void Scanner::ScanLiteralStringChars(bool is_raw, bool remove_whitespace) {
   GrowableArray<int32_t> string_chars(64);
 
   ASSERT(IsScanningString());
@@ -595,6 +590,25 @@
       }
       string_chars.Add(ch1);
     }
+    // The first line of a multi-line string is discarded if it only
+    // contains whitespace.
+    if (remove_whitespace && (string_chars.Last() == '\n')) {
+      bool whitespace_only = true;
+      // Last character is the newline, don't inspect it.
+      const intptr_t len = string_chars.length() - 1;
+      for (int i = 0; i < len; i++) {
+        int32_t ch = string_chars[i];
+        if ((ch != ' ') && (ch != '\t')) {
+          // Non-whitespace character, keep the first line.
+          whitespace_only = false;
+          break;
+        }
+      }
+      if (whitespace_only) {
+        string_chars.Clear();  // Discard characters on first line.
+      }
+      remove_whitespace = false;
+    }
     ReadChar();
   }
 }
@@ -627,7 +641,7 @@
           break;
         }
       } else {
-        ScanLiteralStringChars(false);
+        ScanLiteralStringChars(false, false);
       }
       break;
     }