RFR: 8286895: InternalError: Exception during analyze

[Jan Lahoda]

Consider code like:

Number n = 0;
if (!n instanceof Integer i) {}

javac parses this like:

Number n = 0;
if ((!n) instanceof Integer i) {}


This is obviously erroneous, and will report an error in `Attr`, but if this code gets to `Flow`, like in JShell, then it will split the `inits`/`uninits` of variables to the `true`/`false` inits while processing the unary negation. But, then, the `instanceof` operator will try to declare a variable, which will fail with on an assertion, as that shouldn't be done when the inits are split to `true`/`false`:

Caused by: java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.util.Bits.excl(Bits.java:220)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AssignAnalyzer.newVar(Flow.java:1883)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AssignAnalyzer.visitVarDef(Flow.java:2261)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:1027)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:444)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AssignAnalyzer.scan(Flow.java:1743)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.visitBindingPattern(TreeScanner.java:307)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AssignAnalyzer.visitBindingPattern(Flow.java:2848)
...


The proposed solution is to use `scanExpr` when handling the `instanceof`'s expression, which will merge the `true`/`false` inits, and let the variable be declared.

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

Commit messages:
 - 8286895: InternalError: Exception during analyze

Changes: https://git.openjdk.java.net/jdk/pull/8866/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8866&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286895
  Stats: 31 lines in 4 files changed: 30 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8866.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8866/head:pull/8866

PR: https://git.openjdk.java.net/jdk/pull/8866