https://openjdk.java.net/ 
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 * 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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).
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 * 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,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.nashorn.internal.runtime.linker;



Implements the name mangling and demangling as specified by John Rose's
"Symbolic Freedom in the VM" article. Normally, you would
mangle the names in the call sites as you're generating bytecode, and then
demangle them when you receive them in bootstrap methods.




This code is derived from sun.invoke.util.BytecodeName. Apart from subsetting that
class, we don't want to create dependency between non-exported package from java.base
to nashorn module.



Comment from BytecodeName class reproduced here:

Includes universal mangling rules for the JVM.

Avoiding Dangerous Characters 



The JVM defines a very small set of characters which are illegal
in name spellings.  We will slightly extend and regularize this set
into a group of dangerous characters.
These characters will then be replaced, in mangled names, by escape sequences.
In addition, accidental escape sequences must be further escaped.
Finally, a special prefix will be applied if and only if
the mangling would otherwise fail to begin with the escape character.
This happens to cover the corner case of the null string,
and also clearly marks symbols which need demangling.




Dangerous characters are the union of all characters forbidden
or otherwise restricted by the JVM specification,
plus their mates, if they are brackets
([ and ],
< and >),
plus, arbitrarily, the colon character :.
There is no distinction between type, method, and field names.
This makes it easier to convert between mangled names of different
types, since they do not need to be decoded (demangled).




The escape character is backslash \
(also known as reverse solidus).
This character is, until now, unheard of in bytecode names,
but traditional in the proposed role.



 Replacement Characters 



Every escape sequence is two characters
(in fact, two UTF8 bytes) beginning with
the escape character and followed by a
replacement character.
(Since the replacement character is never a backslash,
iterated manglings do not double in size.)




Each dangerous character has some rough visual similarity
to its corresponding replacement character.
This makes mangled symbols easier to recognize by sight.




The dangerous characters are
/ (forward slash, used to delimit package components),
. (dot, also a package delimiter),
; (semicolon, used in signatures),
$ (dollar, used in inner classes and synthetic members),
< (left angle),
> (right angle),
[ (left square bracket, used in array types),
] (right square bracket, reserved in this scheme for language use),
and : (colon, reserved in this scheme for language use).
Their replacements are, respectively,
| (vertical bar),
, (comma),
? (question mark),
% (percent),
^ (caret),
_ (underscore), and
{ (left curly bracket),
} (right curly bracket),
! (exclamation mark).
In addition, the replacement character for the escape character itself is
- (hyphen),
and the replacement character for the null prefix is
= (equal sign).




An escape character \
followed by any of these replacement characters
is an escape sequence, and there are no other escape sequences.
An equal sign is only part of an escape sequence
if it is the second character in the whole string, following a backslash.
Two consecutive backslashes do not form an escape sequence.




Each escape sequence replaces a so-called original character
which is either one of the dangerous characters or the escape character.
A null prefix replaces an initial null string, not a character.




All this implies that escape sequences cannot overlap and may be
determined all at once for a whole string.  Note that a spelling
string can contain accidental escapes, apparent escape
sequences which must not be interpreted as manglings.
These are disabled by replacing their leading backslash with an
escape sequence (\-).  To mangle a string, three logical steps
are required, though they may be carried out in one pass:



    
  
  1. In each accidental escape, replace the backslash with an escape sequence
(\-).
    2. 
  
  2. Replace each dangerous character with an escape sequence
(\| for /, etc.).
    3. 
  
  3. If the first two steps introduced any change, and
if the string does not already begin with a backslash, prepend a null prefix (\=).
    4. 


To demangle a mangled string that begins with an escape,
remove any null prefix, and then replace (in parallel)
each escape sequence by its original character.

Spelling strings which contain accidental
escapes must have them replaced, even if those
strings do not contain dangerous characters.
This restriction means that mangling a string always
requires a scan of the string for escapes.
But then, a scan would be required anyway,
to check for dangerous characters.



 Nice Properties 



If a bytecode name does not contain any escape sequence,
demangling is a no-op:  The string demangles to itself.
Such a string is called self-mangling.
Almost all strings are self-mangling.
In practice, to demangle almost any name “found in nature”,
simply verify that it does not begin with a backslash.




Mangling is a one-to-one function, while demangling
is a many-to-one function.
A mangled string is defined as validly mangled if
it is in fact the unique mangling of its spelling string.
Three examples of invalidly mangled strings are \=foo,
\-bar, and baz\!, which demangle to foo, \bar, and
baz\!, but then remangle to foo, \bar, and \=baz\-!.
If a language back-end or runtime is using mangled names,
it should never present an invalidly mangled bytecode
name to the JVM.  If the runtime encounters one,
it should also report an error, since such an occurrence
probably indicates a bug in name encoding which
will lead to errors in linkage.
However, this note does not propose that the JVM verifier
detect invalidly mangled names.




As a result of these rules, it is a simple matter to
compute validly mangled substrings and concatenations
of validly mangled strings, and (with a little care)
these correspond to corresponding operations on their
spelling strings.



    
  
  • Any prefix of a validly mangled string is also validly mangled,
although a null prefix may need to be removed.
    • 
  
  • Any suffix of a validly mangled string is also validly mangled,
although a null prefix may need to be added.
    • 
  
  • Two validly mangled strings, when concatenated,
are also validly mangled, although any null prefix
must be removed from the second string,
and a trailing backslash on the first string may need escaping,
if it would participate in an accidental escape when followed
by the first character of the second string.
    • 



If languages that include non-Java symbol spellings use this
mangling convention, they will enjoy the following advantages:



    
  
  • They can interoperate via symbols they share in common.
    • 
  
  • Low-level tools, such as backtrace printers, will have readable displays.
    • 
  
  • Future JVM and language extensions can safely use the dangerous characters
for structuring symbols, but will never interfere with valid spellings.
    • 
  
  • Runtimes and compilers can use standard libraries for mangling and demangling.
    • 
  
  • Occasional transliterations and name composition will be simple and regular,
for classes, methods, and fields.
    • 
  
  • Bytecode names will continue to be compact.
When mangled, spellings will at most double in length, either in
UTF8 or UTF16 format, and most will not change at all.
    • 



 Suggestions for Human Readable Presentations 



For human readable displays of symbols,
it will be better to present a string-like quoted
representation of the spelling, because JVM users
are generally familiar with such tokens.
We suggest using single or double quotes before and after
mangled symbols which are not valid Java identifiers,
with quotes, backslashes, and non-printing characters
escaped as if for literals in the Java language.




For example, an HTML-like spelling
<pre> mangles to
\^pre\_ and could
display more cleanly as
'<pre>',
with the quotes included.
Such string-like conventions are not suitable
for mangled bytecode names, in part because
dangerous characters must be eliminated, rather
than just quoted.  Otherwise internally structured
strings like package prefixes and method signatures
could not be reliably parsed.




In such human-readable displays, invalidly mangled
names should not be demangled and quoted,
for this would be misleading.  Likewise, JVM symbols
which contain dangerous characters (like dots in field
names or brackets in method names) should not be
simply quoted.  The bytecode names
\=phase\,1 and
phase.1 are distinct,
and in demangled displays they should be presented as
'phase.1' and something like
'phase'.1, respectively.



/**
 * <p>
 * Implements the name mangling and demangling as specified by John Rose's
 * <a href="https://blogs.oracle.com/jrose/entry/symbolic_freedom_in_the_vm"
 * target="_blank">"Symbolic Freedom in the VM"</a> article. Normally, you would
 * mangle the names in the call sites as you're generating bytecode, and then
 * demangle them when you receive them in bootstrap methods.
 * </p>
 * <p>
 * This code is derived from sun.invoke.util.BytecodeName. Apart from subsetting that
 * class, we don't want to create dependency between non-exported package from java.base
 * to nashorn module.
 * </p>
 *
 * <h3>Comment from BytecodeName class reproduced here:</h3>
 *
 * Includes universal mangling rules for the JVM.
 *
 * <h3>Avoiding Dangerous Characters </h3>
 *
 * <p>
 * The JVM defines a very small set of characters which are illegal
 * in name spellings.  We will slightly extend and regularize this set
 * into a group of <cite>dangerous characters</cite>.
 * These characters will then be replaced, in mangled names, by escape sequences.
 * In addition, accidental escape sequences must be further escaped.
 * Finally, a special prefix will be applied if and only if
 * the mangling would otherwise fail to begin with the escape character.
 * This happens to cover the corner case of the null string,
 * and also clearly marks symbols which need demangling.
 * </p>
 * <p>
 * Dangerous characters are the union of all characters forbidden
 * or otherwise restricted by the JVM specification,
 * plus their mates, if they are brackets
 * (<code><big><b>[</b></big></code> and <code><big><b>]</b></big></code>,
 * <code><big><b>&lt;</b></big></code> and <code><big><b>&gt;</b></big></code>),
 * plus, arbitrarily, the colon character <code><big><b>:</b></big></code>.
 * There is no distinction between type, method, and field names.
 * This makes it easier to convert between mangled names of different
 * types, since they do not need to be decoded (demangled).
 * </p>
 * <p>
 * The escape character is backslash <code><big><b>\</b></big></code>
 * (also known as reverse solidus).
 * This character is, until now, unheard of in bytecode names,
 * but traditional in the proposed role.
 *
 * </p>
 * <h3> Replacement Characters </h3>
 *
 *
 * <p>
 * Every escape sequence is two characters
 * (in fact, two UTF8 bytes) beginning with
 * the escape character and followed by a
 * <cite>replacement character</cite>.
 * (Since the replacement character is never a backslash,
 * iterated manglings do not double in size.)
 * </p>
 * <p>
 * Each dangerous character has some rough visual similarity
 * to its corresponding replacement character.
 * This makes mangled symbols easier to recognize by sight.
 * </p>
 * <p>
 * The dangerous characters are
 * <code><big><b>/</b></big></code> (forward slash, used to delimit package components),
 * <code><big><b>.</b></big></code> (dot, also a package delimiter),
 * <code><big><b>;</b></big></code> (semicolon, used in signatures),
 * <code><big><b>$</b></big></code> (dollar, used in inner classes and synthetic members),
 * <code><big><b>&lt;</b></big></code> (left angle),
 * <code><big><b>&gt;</b></big></code> (right angle),
 * <code><big><b>[</b></big></code> (left square bracket, used in array types),
 * <code><big><b>]</b></big></code> (right square bracket, reserved in this scheme for language use),
 * and <code><big><b>:</b></big></code> (colon, reserved in this scheme for language use).
 * Their replacements are, respectively,
 * <code><big><b>|</b></big></code> (vertical bar),
 * <code><big><b>,</b></big></code> (comma),
 * <code><big><b>?</b></big></code> (question mark),
 * <code><big><b>%</b></big></code> (percent),
 * <code><big><b>^</b></big></code> (caret),
 * <code><big><b>_</b></big></code> (underscore), and
 * <code><big><b>{</b></big></code> (left curly bracket),
 * <code><big><b>}</b></big></code> (right curly bracket),
 * <code><big><b>!</b></big></code> (exclamation mark).
 * In addition, the replacement character for the escape character itself is
 * <code><big><b>-</b></big></code> (hyphen),
 * and the replacement character for the null prefix is
 * <code><big><b>=</b></big></code> (equal sign).
 * </p>
 * <p>
 * An escape character <code><big><b>\</b></big></code>
 * followed by any of these replacement characters
 * is an escape sequence, and there are no other escape sequences.
 * An equal sign is only part of an escape sequence
 * if it is the second character in the whole string, following a backslash.
 * Two consecutive backslashes do <em>not</em> form an escape sequence.
 * </p>
 * <p>
 * Each escape sequence replaces a so-called <cite>original character</cite>
 * which is either one of the dangerous characters or the escape character.
 * A null prefix replaces an initial null string, not a character.
 * </p>
 * <p>
 * All this implies that escape sequences cannot overlap and may be
 * determined all at once for a whole string.  Note that a spelling
 * string can contain <cite>accidental escapes</cite>, apparent escape
 * sequences which must not be interpreted as manglings.
 * These are disabled by replacing their leading backslash with an
 * escape sequence (<code><big><b>\-</b></big></code>).  To mangle a string, three logical steps
 * are required, though they may be carried out in one pass:
 * </p>
 * <ol>
 *   <li>In each accidental escape, replace the backslash with an escape sequence
 * (<code><big><b>\-</b></big></code>).</li>
 *   <li>Replace each dangerous character with an escape sequence
 * (<code><big><b>\|</b></big></code> for <code><big><b>/</b></big></code>, etc.).</li>
 *   <li>If the first two steps introduced any change, <em>and</em>
 * if the string does not already begin with a backslash, prepend a null prefix (<code><big><b>\=</b></big></code>).</li>
 * </ol>
 *
 * To demangle a mangled string that begins with an escape,
 * remove any null prefix, and then replace (in parallel)
 * each escape sequence by its original character.
 * <p>Spelling strings which contain accidental
 * escapes <em>must</em> have them replaced, even if those
 * strings do not contain dangerous characters.
 * This restriction means that mangling a string always
 * requires a scan of the string for escapes.
 * But then, a scan would be required anyway,
 * to check for dangerous characters.
 *
 * </p>
 * <h3> Nice Properties </h3>
 *
 * <p>
 * If a bytecode name does not contain any escape sequence,
 * demangling is a no-op:  The string demangles to itself.
 * Such a string is called <cite>self-mangling</cite>.
 * Almost all strings are self-mangling.
 * In practice, to demangle almost any name &ldquo;found in nature&rdquo;,
 * simply verify that it does not begin with a backslash.
 * </p>
 * <p>
 * Mangling is a one-to-one function, while demangling
 * is a many-to-one function.
 * A mangled string is defined as <cite>validly mangled</cite> if
 * it is in fact the unique mangling of its spelling string.
 * Three examples of invalidly mangled strings are <code><big><b>\=foo</b></big></code>,
 * <code><big><b>\-bar</b></big></code>, and <code><big><b>baz\!</b></big></code>, which demangle to <code><big><b>foo</b></big></code>, <code><big><b>\bar</b></big></code>, and
 * <code><big><b>baz\!</b></big></code>, but then remangle to <code><big><b>foo</b></big></code>, <code><big><b>\bar</b></big></code>, and <code><big><b>\=baz\-!</b></big></code>.
 * If a language back-end or runtime is using mangled names,
 * it should never present an invalidly mangled bytecode
 * name to the JVM.  If the runtime encounters one,
 * it should also report an error, since such an occurrence
 * probably indicates a bug in name encoding which
 * will lead to errors in linkage.
 * However, this note does not propose that the JVM verifier
 * detect invalidly mangled names.
 * </p>
 * <p>
 * As a result of these rules, it is a simple matter to
 * compute validly mangled substrings and concatenations
 * of validly mangled strings, and (with a little care)
 * these correspond to corresponding operations on their
 * spelling strings.
 * </p>
 * <ul>
 *   <li>Any prefix of a validly mangled string is also validly mangled,
 * although a null prefix may need to be removed.</li>
 *   <li>Any suffix of a validly mangled string is also validly mangled,
 * although a null prefix may need to be added.</li>
 *   <li>Two validly mangled strings, when concatenated,
 * are also validly mangled, although any null prefix
 * must be removed from the second string,
 * and a trailing backslash on the first string may need escaping,
 * if it would participate in an accidental escape when followed
 * by the first character of the second string.</li>
 * </ul>
 * <p>If languages that include non-Java symbol spellings use this
 * mangling convention, they will enjoy the following advantages:
 * </p>
 * <ul>
 *   <li>They can interoperate via symbols they share in common.</li>
 *   <li>Low-level tools, such as backtrace printers, will have readable displays.</li>
 *   <li>Future JVM and language extensions can safely use the dangerous characters
 * for structuring symbols, but will never interfere with valid spellings.</li>
 *   <li>Runtimes and compilers can use standard libraries for mangling and demangling.</li>
 *   <li>Occasional transliterations and name composition will be simple and regular,
 * for classes, methods, and fields.</li>
 *   <li>Bytecode names will continue to be compact.
 * When mangled, spellings will at most double in length, either in
 * UTF8 or UTF16 format, and most will not change at all.</li>
 * </ul>
 *
 *
 * <h3> Suggestions for Human Readable Presentations </h3>
 *
 *
 * <p>
 * For human readable displays of symbols,
 * it will be better to present a string-like quoted
 * representation of the spelling, because JVM users
 * are generally familiar with such tokens.
 * We suggest using single or double quotes before and after
 * mangled symbols which are not valid Java identifiers,
 * with quotes, backslashes, and non-printing characters
 * escaped as if for literals in the Java language.
 * </p>
 * <p>
 * For example, an HTML-like spelling
 * <code><big><b>&lt;pre&gt;</b></big></code> mangles to
 * <code><big><b>\^pre\_</b></big></code> and could
 * display more cleanly as
 * <code><big><b>'&lt;pre&gt;'</b></big></code>,
 * with the quotes included.
 * Such string-like conventions are <em>not</em> suitable
 * for mangled bytecode names, in part because
 * dangerous characters must be eliminated, rather
 * than just quoted.  Otherwise internally structured
 * strings like package prefixes and method signatures
 * could not be reliably parsed.
 * </p>
 * <p>
 * In such human-readable displays, invalidly mangled
 * names should <em>not</em> be demangled and quoted,
 * for this would be misleading.  Likewise, JVM symbols
 * which contain dangerous characters (like dots in field
 * names or brackets in method names) should not be
 * simply quoted.  The bytecode names
 * <code><big><b>\=phase\,1</b></big></code> and
 * <code><big><b>phase.1</b></big></code> are distinct,
 * and in demangled displays they should be presented as
 * <code><big><b>'phase.1'</b></big></code> and something like
 * <code><big><b>'phase'.1</b></big></code>, respectively.
 * </p>
 */
public final class NameCodec {
    private NameCodec() {
    }

    private static final char ESCAPE_C = '\\';
    // empty escape sequence to avoid a null name or illegal prefix
    private static final char NULL_ESCAPE_C = '=';
    private static final String NULL_ESCAPE = ESCAPE_C+""+NULL_ESCAPE_C;

    
Canonical encoding for the empty name.

/**
     * Canonical encoding for the empty name.
     */
    public static final String EMPTY_NAME =  new String(new char[] { ESCAPE_C, NULL_ESCAPE_C });

    
Encodes ("mangles") an unencoded symbolic name.

Params:
  • name – the symbolic name to mangle
Returns:the mangled form of the symbolic name.
/**
     * Encodes ("mangles") an unencoded symbolic name.
     * @param name the symbolic name to mangle
     * @return the mangled form of the symbolic name.
     */
    public static String encode(final String name) {
        final String bn = mangle(name);
        assert((Object)bn == name || looksMangled(bn)) : bn;
        assert(name.equals(decode(bn))) : name;
        return bn;
    }

    
Decodes ("demangles") an encoded symbolic name.

Params:
  • name – the symbolic name to demangle
Returns:the demangled form of the symbolic name.
/**
     * Decodes ("demangles") an encoded symbolic name.
     * @param name the symbolic name to demangle
     * @return the demangled form of the symbolic name.
     */
    public static String decode(final String name) {
        String sn = name;
        if (!sn.isEmpty() && looksMangled(name)) {
            sn = demangle(name);
            assert(name.equals(mangle(sn))) : name+" => "+sn+" => "+mangle(sn);
        }
        return sn;
    }

    private static boolean looksMangled(final String s) {
        return s.charAt(0) == ESCAPE_C;
    }

    private static String mangle(final String s) {
        if (s.length() == 0)
            return NULL_ESCAPE;

        // build this lazily, when we first need an escape:
        StringBuilder sb = null;

        for (int i = 0, slen = s.length(); i < slen; i++) {
            final char c = s.charAt(i);

            boolean needEscape = false;
            if (c == ESCAPE_C) {
                if (i+1 < slen) {
                    final char c1 = s.charAt(i+1);
                    if ((i == 0 && c1 == NULL_ESCAPE_C)
                        || c1 != originalOfReplacement(c1)) {
                        // an accidental escape
                        needEscape = true;
                    }
                }
            } else {
                needEscape = isDangerous(c);
            }

            if (!needEscape) {
                if (sb != null)  sb.append(c);
                continue;
            }

            // build sb if this is the first escape
            if (sb == null) {
                sb = new StringBuilder(s.length()+10);
                // mangled names must begin with a backslash:
                if (s.charAt(0) != ESCAPE_C && i > 0)
                    sb.append(NULL_ESCAPE);
                // append the string so far, which is unremarkable:
                sb.append(s, 0, i);
            }

            // rewrite \ to \-, / to \|, etc.
            sb.append(ESCAPE_C);
            sb.append(replacementOf(c));
        }

        if (sb != null)   return sb.toString();

        return s;
    }

    private static String demangle(final String s) {
        // build this lazily, when we first meet an escape:
        StringBuilder sb = null;

        int stringStart = 0;
        if (s.startsWith(NULL_ESCAPE))
            stringStart = 2;

        for (int i = stringStart, slen = s.length(); i < slen; i++) {
            char c = s.charAt(i);

            if (c == ESCAPE_C && i+1 < slen) {
                // might be an escape sequence
                final char rc = s.charAt(i+1);
                final char oc = originalOfReplacement(rc);
                if (oc != rc) {
                    // build sb if this is the first escape
                    if (sb == null) {
                        sb = new StringBuilder(s.length());
                        // append the string so far, which is unremarkable:
                        sb.append(s, stringStart, i);
                    }
                    ++i;  // skip both characters
                    c = oc;
                }
            }

            if (sb != null)
                sb.append(c);
        }

        if (sb != null)   return sb.toString();

        return s.substring(stringStart);
    }

    private static final String DANGEROUS_CHARS   = "\\/.;:$[]<>"; // \\ must be first
    private static final String REPLACEMENT_CHARS =  "-|,?!%{}^_";
    private static final int DANGEROUS_CHAR_FIRST_INDEX = 1; // index after \\

    private static final long[] SPECIAL_BITMAP = new long[2];  // 128 bits
    static {
        final String SPECIAL = DANGEROUS_CHARS + REPLACEMENT_CHARS;
        for (final char c : SPECIAL.toCharArray()) {
            SPECIAL_BITMAP[c >>> 6] |= 1L << c;
        }
    }

    private static boolean isSpecial(final char c) {
        if ((c >>> 6) < SPECIAL_BITMAP.length)
            return ((SPECIAL_BITMAP[c >>> 6] >> c) & 1) != 0;
        else
            return false;
    }

    private static char replacementOf(final char c) {
        if (!isSpecial(c))  return c;
        final int i = DANGEROUS_CHARS.indexOf(c);
        if (i < 0)  return c;
        return REPLACEMENT_CHARS.charAt(i);
    }

    private static char originalOfReplacement(final char c) {
        if (!isSpecial(c))  return c;
        final int i = REPLACEMENT_CHARS.indexOf(c);
        if (i < 0)  return c;
        return DANGEROUS_CHARS.charAt(i);
    }

    private static boolean isDangerous(final char c) {
        if (!isSpecial(c))  return false;
        return (DANGEROUS_CHARS.indexOf(c) >= DANGEROUS_CHAR_FIRST_INDEX);
    }
}