# HG changeset patch
# User Tom Rodriguez <tom.rodriguez@oracle.com>
# Date 1420768597 28800
# Node ID 650934ca71578571600d2932171ba0dc8813bf9d
# Parent  750db34c9fe177c5b5b5790fef250c1b1610cc54
Mark the first difference when comparing graph strings

diff -r 750db34c9fe1 -r 650934ca7157 graal/com.oracle.graal.compiler.test/src/com/oracle/graal/compiler/test/GraalCompilerTest.java
--- a/graal/com.oracle.graal.compiler.test/src/com/oracle/graal/compiler/test/GraalCompilerTest.java	Thu Jan 08 10:20:07 2015 -0800
+++ b/graal/com.oracle.graal.compiler.test/src/com/oracle/graal/compiler/test/GraalCompilerTest.java	Thu Jan 08 17:56:37 2015 -0800
@@ -231,7 +231,7 @@
     protected void assertEquals(StructuredGraph expected, StructuredGraph graph, boolean excludeVirtual, boolean checkConstants) {
         String expectedString = getCanonicalGraphString(expected, excludeVirtual, checkConstants);
         String actualString = getCanonicalGraphString(graph, excludeVirtual, checkConstants);
-        String mismatchString = "mismatch in graphs:\n========= expected (" + expected + ") =========\n" + expectedString + "\n\n========= actual (" + graph + ") =========\n" + actualString;
+        String mismatchString = compareGraphStrings(expected, expectedString, graph, actualString);
 
         if (!excludeVirtual && getNodeCountExcludingUnusedConstants(expected) != getNodeCountExcludingUnusedConstants(graph)) {
             Debug.dump(expected, "Node count not matching - expected");
@@ -245,6 +245,42 @@
         }
     }
 
+    private static String compareGraphStrings(StructuredGraph expectedGraph, String expectedString, StructuredGraph actualGraph, String actualString) {
+        if (!expectedString.equals(actualString)) {
+            String[] expectedLines = expectedString.split("\n");
+            String[] actualLines = actualString.split("\n");
+            int diffIndex = -1;
+            int limit = Math.min(actualLines.length, expectedLines.length);
+            String marker = " <<<";
+            for (int i = 0; i < limit; i++) {
+                if (!expectedLines[i].equals(actualLines[i])) {
+                    diffIndex = i;
+                    break;
+                }
+            }
+            if (diffIndex == -1) {
+                // Prefix is the same so add some space after the prefix
+                diffIndex = limit;
+                if (actualLines.length == limit) {
+                    actualLines = Arrays.copyOf(actualLines, limit + 1);
+                    actualLines[diffIndex] = "";
+                } else {
+                    assert expectedLines.length == limit;
+                    expectedLines = Arrays.copyOf(expectedLines, limit + 1);
+                    expectedLines[diffIndex] = "";
+                }
+            }
+            // Place a marker next to the first line that differs
+            expectedLines[diffIndex] = expectedLines[diffIndex] + marker;
+            actualLines[diffIndex] = actualLines[diffIndex] + marker;
+            String ediff = String.join("\n", expectedLines);
+            String adiff = String.join("\n", actualLines);
+            return "mismatch in graphs:\n========= expected (" + expectedGraph + ") =========\n" + ediff + "\n\n========= actual (" + actualGraph + ") =========\n" + adiff;
+        } else {
+            return "mismatch in graphs";
+        }
+    }
+
     protected void assertConstantReturn(StructuredGraph graph, int value) {
         String graphString = getCanonicalGraphString(graph, false, true);
         Assert.assertEquals("unexpected number of ReturnNodes: " + graphString, graph.getNodes(ReturnNode.class).count(), 1);