8017611: Auto corrector for mistyped vm options

The auto corrector for mistyped vm options fuzzy-matches existing flags based on string similarity (Dice's coefficient).

Reviewed-by: kvn, dsamersoff, hseigel, johnc

hotspot/src/share/vm/runtime/arguments.cpp

@@ -849,7 +849,7 @@ bool Arguments::process_argument(const char* arg,
     arg_len = equal_sign - argname;
   }
 
-  Flag* found_flag = Flag::find_flag((char*)argname, arg_len, true);
+  Flag* found_flag = Flag::find_flag((const char*)argname, arg_len, true);
   if (found_flag != NULL) {
     char locked_message_buf[BUFLEN];
     found_flag->get_locked_message(locked_message_buf, BUFLEN);
@@ -870,6 +870,14 @@ bool Arguments::process_argument(const char* arg,
   } else {
     jio_fprintf(defaultStream::error_stream(),
                 "Unrecognized VM option '%s'\n", argname);
+    Flag* fuzzy_matched = Flag::fuzzy_match((const char*)argname, arg_len, true);
+    if (fuzzy_matched != NULL) {
+      jio_fprintf(defaultStream::error_stream(),
+                  "Did you mean '%s%s%s'?\n",
+                  (fuzzy_matched->is_bool()) ? "(+/-)" : "",
+                  fuzzy_matched->name,
+                  (fuzzy_matched->is_bool()) ? "" : "=<value>");
+    }
   }
 
   // allow for commandline "commenting out" options like -XX:#+Verbose

hotspot/src/share/vm/runtime/globals.cpp

@@ -276,14 +276,14 @@ static Flag flagTable[] = {
 Flag* Flag::flags = flagTable;
 size_t Flag::numFlags = (sizeof(flagTable) / sizeof(Flag));
 
-inline bool str_equal(const char* s, char* q, size_t len) {
+inline bool str_equal(const char* s, const char* q, size_t len) {
   // s is null terminated, q is not!
   if (strlen(s) != (unsigned int) len) return false;
   return strncmp(s, q, len) == 0;
 }
 
 // Search the flag table for a named flag
-Flag* Flag::find_flag(char* name, size_t length, bool allow_locked) {
+Flag* Flag::find_flag(const char* name, size_t length, bool allow_locked) {
   for (Flag* current = &flagTable[0]; current->name != NULL; current++) {
     if (str_equal(current->name, name, length)) {
       // Found a matching entry.  Report locked flags only if allowed.
@@ -301,6 +301,52 @@ Flag* Flag::find_flag(char* name, size_t length, bool allow_locked) {
   return NULL;
 }
 
+// Compute string similarity based on Dice's coefficient
+static float str_similar(const char* str1, const char* str2, size_t len2) {
+  int len1 = (int) strlen(str1);
+  int total = len1 + (int) len2;
+
+  int hit = 0;
+
+  for (int i = 0; i < len1 -1; ++i) {
+    for (int j = 0; j < (int) len2 -1; ++j) {
+      if ((str1[i] == str2[j]) && (str1[i+1] == str2[j+1])) {
+        ++hit;
+        break;
+      }
+    }
+  }
+
+  return 2.0f * (float) hit / (float) total;
+}
+
+Flag* Flag::fuzzy_match(const char* name, size_t length, bool allow_locked) {
+  float VMOptionsFuzzyMatchSimilarity = 0.7f;
+  Flag* match = NULL;
+  float score;
+  float max_score = -1;
+
+  for (Flag* current = &flagTable[0]; current->name != NULL; current++) {
+    score = str_similar(current->name, name, length);
+    if (score > max_score) {
+      max_score = score;
+      match = current;
+    }
+  }
+
+  if (!(match->is_unlocked() || match->is_unlocker())) {
+    if (!allow_locked) {
+      return NULL;
+    }
+  }
+
+  if (max_score < VMOptionsFuzzyMatchSimilarity) {
+    return NULL;
+  }
+
+  return match;
+}
+
 // Returns the address of the index'th element
 static Flag* address_of_flag(CommandLineFlagWithType flag) {
   assert((size_t)flag < Flag::numFlags, "bad command line flag index");

hotspot/src/share/vm/runtime/globals.hpp

@@ -220,7 +220,8 @@ struct Flag {
   // number of flags
   static size_t numFlags;
 
-  static Flag* find_flag(char* name, size_t length, bool allow_locked = false);
+  static Flag* find_flag(const char* name, size_t length, bool allow_locked = false);
+  static Flag* fuzzy_match(const char* name, size_t length, bool allow_locked = false);
 
   bool is_bool() const        { return strcmp(type, "bool") == 0; }
   bool get_bool() const       { return *((bool*) addr); }

hotspot/test/gc/arguments/TestUnrecognizedVMOptionsHandling.java

@@ -0,0 +1,69 @@
+/*
+* Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
+* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+*
+* This code is free software; you can redistribute it and/or modify it
+* under the terms of the GNU General Public License version 2 only, as
+* published by the Free Software Foundation.
+*
+* This code is distributed in the hope that it will be useful, but WITHOUT
+* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+* version 2 for more details (a copy is included in the LICENSE file that
+* accompanied this code).
+*
+* You should have received a copy of the GNU General Public License version
+* 2 along with this work; if not, write to the Free Software Foundation,
+* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+*
+* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+* or visit www.oracle.com if you need additional information or have any
+* questions.
+*/
+
+/*
+ * @test TestUnrecognizedVMOptionsHandling
+ * @key gc
+ * @bug 8017611
+ * @summary Tests handling unrecognized VM options
+ * @library /testlibrary
+ * @run main/othervm TestUnrecognizedVMOptionsHandling
+ */
+
+import com.oracle.java.testlibrary.*;
+
+public class TestUnrecognizedVMOptionsHandling {
+
+  public static void main(String args[]) throws Exception {
+    // The first two JAVA processes are expected to fail, but with a correct VM option suggestion
+    ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+      "-XX:+PrintGc",
+      "-version"
+      );
+    OutputAnalyzer outputWithError = new OutputAnalyzer(pb.start());
+    outputWithError.shouldContain("Did you mean '(+/-)PrintGC'?");
+    if (outputWithError.getExitValue() == 0) {
+      throw new RuntimeException("Not expected to get exit value 0");
+    }
+
+    pb = ProcessTools.createJavaProcessBuilder(
+      "-XX:MaxiumHeapSize=500m",
+      "-version"
+      );
+    outputWithError = new OutputAnalyzer(pb.start());
+    outputWithError.shouldContain("Did you mean 'MaxHeapSize=<value>'?");
+    if (outputWithError.getExitValue() == 0) {
+      throw new RuntimeException("Not expected to get exit value 0");
+    }
+
+    // The last JAVA process should run successfully for the purpose of sanity check
+    pb = ProcessTools.createJavaProcessBuilder(
+      "-XX:+PrintGC",
+      "-version"
+      );
+    OutputAnalyzer outputWithNoError = new OutputAnalyzer(pb.start());
+    outputWithNoError.shouldNotContain("Did you mean '(+/-)PrintGC'?");
+    outputWithNoError.shouldHaveExitValue(0);
+  }
+}
+