From 0c8ac1a52dcf0a93e6e1ab4d701215b2beb6cff6 Mon Sep 17 00:00:00 2001
From: Eliot Horowitz <eliot@10gen.com>
Date: Thu, 28 Feb 2013 16:43:45 -0500
Subject: SERVER-8758 - IndexSet fix for ab vs a

---
 src/mongo/db/index_set.cpp      | 16 ++++++++++++++--
 src/mongo/db/index_set.h        |  3 +++
 src/mongo/db/index_set_test.cpp |  7 +++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/mongo/db/index_set.cpp b/src/mongo/db/index_set.cpp
index 4d7cb62a759..65f74ed54ea 100644
--- a/src/mongo/db/index_set.cpp
+++ b/src/mongo/db/index_set.cpp
@@ -47,16 +47,28 @@ namespace mongo {
 
             StringData idx( *i );
 
-            if ( use.startsWith( idx ) )
+            if ( _startsWith( use, idx ) )
                 return true;
 
-            if ( idx.startsWith( use ) )
+            if ( _startsWith( idx, use ) )
                 return true;
         }
 
         return false;
     }
 
+    bool IndexPathSet::_startsWith( const StringData& a, const StringData& b ) const {
+        if ( !a.startsWith( b ) )
+            return false;
+
+        // make sure there is a dot or EOL right after
+
+        if ( a.size() == b.size() )
+            return true;
+
+        return a[b.size()] == '.';
+    }
+
     bool getCanonicalIndexField( const StringData& fullName, string* out ) {
         // check if fieldName contains ".$" or ".###" substrings (#=digit) and skip them
         // however do not skip the first field even if it meets these criteria
diff --git a/src/mongo/db/index_set.h b/src/mongo/db/index_set.h
index 24717750e9a..1ff99780f07 100644
--- a/src/mongo/db/index_set.h
+++ b/src/mongo/db/index_set.h
@@ -39,6 +39,9 @@ namespace mongo {
         bool mightBeIndexed( const StringData& path ) const;
 
     private:
+
+        bool _startsWith( const StringData& a, const StringData& b ) const;
+
         std::set<std::string> _canonical;
     };
 
diff --git a/src/mongo/db/index_set_test.cpp b/src/mongo/db/index_set_test.cpp
index aac5b43550b..28a1d9fe68e 100644
--- a/src/mongo/db/index_set_test.cpp
+++ b/src/mongo/db/index_set_test.cpp
@@ -33,6 +33,13 @@ namespace mongo {
         ASSERT_FALSE( a.mightBeIndexed( "a.c" ) );
     }
 
+    TEST( IndexPathSetTest, Simple2 ) {
+        IndexPathSet a;
+        a.addPath( "ab" );
+        ASSERT_FALSE( a.mightBeIndexed( "a" ) );
+    }
+
+
     TEST( IndexPathSetTest, getCanonicalIndexField1 ) {
         string x;
 
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