RFR: 8372336: javac fails with an exception when a class is missing while evaluating conditional expression

[Jan Lahoda]

Consider library code like:

package test;
public class Intermediate extends Base {}
package test;
public class Base {}


this is compiled, but the `Base` is missing/deleted. Now consider use of this library:

package test;
public class Test {
    private void test(Intermediate i) {
        int j = i != null ? i.get() : -1;
    }
}


This fails with:

java.lang.NullPointerException: Cannot invoke "com.sun.tools.javac.code.Symbol.flags()" because "sym" is null
        at jdk.compiler/com.sun.tools.javac.code.Types.memberType(Types.java:2304)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.isBooleanOrNumeric(Attr.java:2143)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.isBooleanOrNumeric(Attr.java:2132)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.visitConditional(Attr.java:2070)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCConditional.accept(JCTree.java:1580)
        at jdk.compiler/com.sun.tools.javac.comp.Attr.attribTree(Attr.java:677)
...


When attributing `i.get()`, there's a `CompletionFailure` thrown, for the missing `Base`. That is OK, but in this case, the `CompletionFailure` is caught by `Attr.attribTree`, but the problem is that the AST for the method invocation does not have the `Symbol`s filled in. But `isBooleanOrNumeric` relies on a non-`null` `Symbol`:
https://github.com/openjdk/jdk/blob/49176e322bbb9ed1ef2f534b949b937770b54162/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java#L2147

It would be possible to add a `null` check into `isBooleanOrNumeric`, but it seems more reliable to catch the `CompletionFailure` a bit sooner, and fill in the `Symbol` for the invocation. This is closer to what is being done in other similar cases.

-------------

Commit messages:
 - 8372336: javac fails with an exception when a class is missing while evaluating conditional expression

Changes: https://git.openjdk.org/jdk/pull/28490/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28490&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372336
  Stats: 104 lines in 2 files changed: 102 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28490.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28490/head:pull/28490

PR: https://git.openjdk.org/jdk/pull/28490