RFR: 8297158: Suspicious collection method call in Types.isSameTypeVisitor

[Vicente Romero]

As reported there is a code in `com.sun.tools.javac.code.Types` that was basically a no-op. The code in question is:


    if (tMap.containsKey(ti)) {
        throw new AssertionError("Malformed intersection");
    }
    tMap.put(ti.tsym, ti); 

where tMap is defined as: `Map<Symbol,Type>`, but `ti` is a type so the condition, `tMap.containsKey(ti)`, is always false. The assertion should be thrown if an intersection type has two or more repeated interfaces. But there are other places in the compiler where this is checked for and an error is issued. So it shouldn't be possible to get to this point during a compilation. There are several tests, including combo tests, already stressing this code for this reason there is no need to add more regression tests.

TIA

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Commit messages:
 - 8297158: Suspicious collection method call in Types.isSameTypeVisitor

Changes: https://git.openjdk.org/jdk/pull/12279/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12279&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297158
  Stats: 9 lines in 4 files changed: 0 ins; 3 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/12279.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12279/head:pull/12279

PR: https://git.openjdk.org/jdk/pull/12279