[GROOVY-10277] STC fails to catch type error on the return type of lambdas

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-rc-1
• Component/s: Static Type Checker
• Assignee: Eric Milles
• Reporter: Thodoris Sotiropoulos
• Created: 01/Oct/21 15:27
• Updated: 06/Jun/23 18:32
• Resolved: 16/Nov/21 18:29

Description

I have the following program

import java.util.function.Supplier;


class Main {
  static void main(String[] args) {
    bar({ -> true}); // should not type-check
    bar({ -> true} as Supplier<Long>); // should not type-check.
  }

  static Long bar(Supplier<Long> x) {
    x.get()
  }
}

Actual behaviour

The compiler mistakenly compiles this program, but produces a CCE at runtime.

Exception in thread "main" org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'true' with class 'java.lang.Boolean' to class 'java.lang.Long'
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToNumber(DefaultTypeTransformation.java:182)
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.continueCastOnNumber(DefaultTypeTransformation.java:294)
        at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToType(DefaultTypeTransformation.java:251)
        at org.codehaus.groovy.vmplugin.v8.IndyInterface.fromCache(IndyInterface.java:318)
        at Main.bar(test.groovy:10)
        at Main.main(test.groovy:6)

Expected behaviour

The compiler should reject this program.

Tested against master.
Also note that this bug exists since Groovy v3.0.8.

Issue Links

• relates to: GROOVY-8168 When using Interface: BigDecimal cannot be cast to Double
• relates to: GROOVY-10372 STC: check lambda or closure parameter types against target method