[GROOVY-8255] Odd problems with flow typing and generics in Groovy 2.4.12+

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.12
• Fix Version/s: 2.4.13
• Component/s: Static Type Checker
• Assignee: Paul King
• Reporter: Graeme Rocher
• Created: 14/Jul/17 10:35
• Updated: 06/Mar/18 23:12
• Resolved: 14/Nov/17 13:44

Description

In order to get the GORM codebase to compile I had to make this change:

https://github.com/grails/grails-data-mapping/commit/1ef850c496d13d8ca915b27e76b6bfdb4e27377e

The code in question is:

    /**
     * Sets multipart values within the request body
     *
     * @param name The name of the multipart
     * @param value The value of the multipart
     */
    void setProperty(String name, value) {
        if (value instanceof File) {
            value = new FileSystemResource(value)
        }
        else if (value instanceof URL) {
            value = new UrlResource(value)
        }
        else if (value instanceof InputStream) {
            value = new InputStreamResource(value)
        }
        else if (value instanceof GString) {
            value = value.toString()
        }
        if( mvm[name] ) {
            mvm[name].add value    
        }
        else {
            mvm.put(name, [value]) // <--- FAILS COMPILATION HERE
        }        
    }

No matter what I tried I could not get it into to compile. The method accepts `put(String, List<Object>)` but fails compilation with:

RequestCustomizer.groovy: 392: [Static type checking] - Cannot call org.springframework.util.MultiValueMap <String, Object>#put(java.lang.String, java.lang.Object) with arguments [java.lang.String, java.util.List <java.lang.String>] 
 @ line 392, column 13.
               mvm.put(name, [value])
               ^

Altering the code to:

       List<Object> values = [value]
       mvm.put(name, values)

Fails with:

RequestCustomizer.groovy: 392: [Static type checking] - Incompatible generic argument types. Cannot assign java.util.List <java.lang.String> to: java.util.List <Object>
 @ line 392, column 35.
               List<Object> values = [value]
                                     ^

RequestCustomizer.groovy: 393: [Static type checking] - Cannot call org.springframework.util.MultiValueMap <String, Object>#put(java.lang.String, java.lang.Object) with arguments [java.lang.String, java.util.List <java.lang.String>] 
 @ line 393, column 13.
               mvm.put(name, values)
               ^

2 errors

Issue Links

• links to: GitHub Pull Request #635