8354908: javac mishandles supplementary character in character literal

[lahodaj]

Some Unicode characters consist of two surrogates, i.e. two chars. And, such Unicode characters cannot be part of a char literal, as there's no way to represent them as a character literal. But, javac currently accepts code with such characters, and only puts the char, the high surrogate, into the literal, ignoring the second one.

For example, the JDK 24 behavior is:

$ cat /tmp/T.java 
public class T {
    public static void main(String... args) {
       char c = '😊';
       System.err.println(Integer.toHexString((int) c));
       System.err.println(Character.isHighSurrogate(c));
    }
}
$ java /tmp/T.java
d83d
true

But, in JDK 11, such literals have been rejected:

$ java /tmp/T.java
/tmp/T.java:3: error: unclosed character literal
       char c = '😊';
                ^
/tmp/T.java:3: error: illegal character: '\ude0a'
       char c = '😊';
                  ^
/tmp/T.java:3: error: unclosed character literal
       char c = '😊';
                   ^
3 errors
error: compilation failed

The proposal in this PR is to explicitly check for this case when scanning character literal, and produce explicit error when a multi-surrogate character is used. javac will produce an error like:

$ java /tmp/T.java
/tmp/T.java:3: error: character literal contains more than one UTF-16 code point
       char c = '😊';
                ^
1 error
error: compilation failed

---

Progress

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• Change requires CSR request JDK-8355978 to be approved
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Warning

 ⚠️ Found leading lowercase letter in issue title for 8354908: javac mishandles supplementary character in character literal

Issues

• JDK-8354908: javac mishandles supplementary character in character literal (Bug - P4)
• JDK-8355978: javac mishandles supplementary character in character literal (CSR)

Reviewers

• Vicente Romero (@vicente-romero-oracle - Reviewer) Review applies to ae1201b3
• Naoto Sato (@naotoj - Reviewer)

Reviewing

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8354908: javac mishandles supplementary character in character literal

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• b6b5ac1: 8348351: Improve lazy initialization of the available currencies set
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[vicente-romero-oracle]

lgtm

[naotoj]

The error message is kind of vague. How about using "surrogate code point"?
https://www.unicode.org/glossary/#surrogate_code_point

[naotoj]

Or "UTF-16 code unit"?

[lahodaj]

/integrate

[openjdk]

Going to push as commit 03dca03.
Since your change was applied there have been 258 commits pushed to the master branch:

• 6e08469: 8356658: java/foreign/TestBufferStackStress2.java failed again with junit action timed out
• 24d77ad: 8356057: PrintingProcessor (-Xprint) does not print type variable bounds and type annotations for Object supertypes
• 4fc10a1: 8356087: Problematic KeyInfo check using key algorithm in P11SecretKeyFactory class
• ... and 255 more: https://git.openjdk.org/jdk/compare/3140de411bb55604f8a9e2484798098d9d141002...master

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[openjdk]

@lahodaj Pushed as commit 03dca03.

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