Per the Official Google Blog:

Code Search, which was designed to help people search for open source code all over the web, will be shut down along with the Code Search API on January 15, 2012.

Google Code Search is now gone, and since that makes it much harder to understand the features it presented, here's my attempt to render them via information I gathered from a cache of the page for the Search Options:

The "In Search Box" just notes the syntax to type the command directly in the main search box instead of using the advance search interface.

• Package (In Search Box: "package:linux-2.6")
• Language (In Search Box: "lang:c++")
  • (OPTIONS: any language, actionscript, ada, applescript, asp, assembly, autoconf, automake, awk, basic, bat, c, c#, c++, caja, cobol, coldfusion, configure, css, d, eiffel, erlang, fortran, go, haskell, inform, java, java, javascript, jsp, lex, limbo, lisp, lolcode, lua, m4, makefile, maple, mathematica, matlab, messagecatalog, modula2, modula3, objectivec, ocaml, pascal, perl, php, pod, prolog, proto, python, python, r, rebol, ruby, sas, scheme, scilab, sgml, shell, smalltalk, sml, sql, svg, tcl, tex, texinfo, troff, verilog, vhdl, vim, xslt, xul, yacc)
• File (In Search Box: "file:^.*.java$")
• Class (In Search Box: "class:HashMap")
• Function (In Search Box: "function:toString")
• License (In Search Box: "license:mozilla")
  • (OPTIONS: null/any-license, aladdin/Aladdin-Public-License, artistic/Artistic-License, apache/Apache-License, apple/Apple-Public-Source-License, bsd/BSD-License, cpl/Common-Public-License, epl/Eclipse-Public-License, agpl/GNU-Affero-General-Public-License, gpl/GNU-General-Public-License, lgpl/GNU-Lesser-General-Public-License, disclaimer/Historical-Permission-Notice-and-Disclaimer, ibm/IBM-Public-License, lucent/Lucent-Public-License, mit/MIT-License, mozilla/Mozilla-Public-License, nasa/NASA-Open-Source-Agreement, python/Python-Software-Foundation-License, qpl/Q-Public-License, sleepycat/Sleepycat-License, zope/Zope-Public-License)
• Case Sensitive (In Search Box: "case:no")
  • (OPTIONS: yes, no)

Also of use in understanding the search tool would be the still live FAQs page for Google Code Search.

Is there any code search engine that would fully replace Google Code Search's features?