[Truffle] Add Thread::Backtrace::Location#lineno.

Author: bjfish

spec/truffle/tags/core/thread/backtrace/location/absolute_path_tags.txt

@@ -297,7 +297,7 @@ public RubySymbol calleeName(VirtualFrame frame) {
         }
     }
 
-    @CoreMethod(names = "caller_locations", isModuleFunction = true, optional = 2)
+    @CoreMethod(names = "caller_locations", isModuleFunction = true, optional = 2, lowerFixnumParameters = {0, 1})
     public abstract static class CallerLocationsNode extends CoreMethodArrayArgumentsNode {
 
         public CallerLocationsNode(RubyContext context, SourceSection sourceSection) {

spec/truffle/tags/core/thread/backtrace/location/lineno_tags.txt

@@ -88,6 +88,25 @@ public RubyString absolutePath(RubyBasicObject threadBacktraceLocation) {
 
     }
 
+    @CoreMethod(names = "lineno")
+    public abstract static class LinenoNode extends UnaryCoreMethodNode {
+
+        public LinenoNode(RubyContext context, SourceSection sourceSection) {
+            super(context, sourceSection);
+        }
+
+        @CompilerDirectives.TruffleBoundary
+        @Specialization
+        public int lineno(RubyBasicObject threadBacktraceLocation) {
+            final Activation activation = getActivation(threadBacktraceLocation);
+
+            final SourceSection sourceSection = activation.getCallNode().getEncapsulatingSourceSection();
+
+            return sourceSection.getStartLine();
+        }
+
+    }
+
     @CoreMethod(names = {"to_s", "inspect"})
     public abstract static class ToSNode extends UnaryCoreMethodNode {