Fix unchecked conversion not failed compilation

[chrisrueger]

Closes #4957

What it does

• Detect when any explicit type argument is a raw type and then fail compilation (to achieve same compilation error as javac)
• This seems to be related to https://docs.oracle.com/javase/specs/jls/se21/html/jls-15.html#jls-15.12.2.6
• Adds regression test testGH4957 reproducing the Comparator.comparing + raw Comparable scenario With this fix testGH4957 passes.

How to test

• run org.eclipse.jdt.core.tests.compiler.regression.GenericsRegressionTest_9.testGH4957() without the fix in org.eclipse.jdt.internal.compiler.lookup.ParameterizedGenericMethodBinding.computeCompatibleMethod(MethodBinding, TypeBinding[], Scope, InvocationSite)

or just use e.g. Eclipse 2025-03 (or even 2026-06 (4.40) Build id: I20260319-1800 master) and paste the the following class:

import java.util.Comparator;
import java.util.Map;

public class Snippet {

    public static void main(String[] args) {

        Comparator<Map<String, Object>> eventComparator = Comparator
            .<Map<String, Object>, Comparable>comparing(e -> (Comparable) e.get("event_date"),
                Comparator.nullsLast(Comparator.naturalOrder()))
            .thenComparing(e -> (String) e.get("event_type"));
    }

}

Expected Result: Compilation should fail in Eclipse
Actual result: Compiliation succeeds.

But in javacc compilation fails.

With this PR compilation fails also in Eclipse.

But note: Eclipse seems to error with a different message than javac. Not sure this is a deeper problem. But at least it fails at the same place.

ECJ fails with:

"5. ERROR in Snippet.java (at line 11)\n" +
			"	.thenComparing(e -> (String) e.get(\"event_type\"));\n" +
			"	                               ^^^\n" +
			"The method get(String) is undefined for the type Object\n" +

while javac failed with:

Snippet.java:13: error: cannot find symbol
            .thenComparing(e -> (String) e.get("event_type"));
                                          ^
  symbol:   method get(String)
  location: variable e of type Object
Snippet.java:13: warning: [unchecked] unchecked conversion
            .thenComparing(e -> (String) e.get("event_type"));
                          ^
  required: Comparator<Map<String,Object>>
  found:    Comparator
1 error
5 warnings
error: compilation failed

Disclaimer:

I used AI to help me understand the issue and spec and find the places in the code. I have manually tested and debugged via latest JDT Dev environment via Oomph and ran my test in Eclipse.
This is my first step in the compiler space. Feel free to reject it or just use it as a base for a better fix if needed.

Author checklist

• I have thoroughly tested my changes as good as I can
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)

[venkateshkona3456-oss]

Hello,
I would like to work on this issue. Is it available?

Thank you!