[GROOVY-11058] plus() on UnmodifiableMap returns a new Map with changed data

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.4.21, 2.5.14, 3.0.9, 4.0.12
• Component/s: Groovy Console
• Assignee: Unassigned
• Reporter: Jim Klimov
• Created: 15/May/23 12:30
• Updated: 16/May/23 13:07

Description

Groovy UnmodifiableMap.plus() operations return a different Map class and modified data in the object, compromising common syntax like myView += myMap (which can happen e.g. during script refactoring from maps to read-only views and should throw when misused).

Originally found in Jenkins with its built-in old groovy-2.4.21 (in-core for pipeline scripts) and http://tpcg.io/_R7VESY, but verified with a newer 2.5.14 version at e.g. https://groovyconsole.appspot.com/script/4819062429319168 (see "Output" tab since it shows stack trace by default) and groovy-3.0.9/jvm-17.0.1 as seen at https://jdoodle.com/ia/HVH and double-checked locally with GroovyConsole from a freshly fetched 4.0.12 tarball.

 

// Repro case for Groovy
println GroovySystem.version

def m1 = [t: 'somestring', n: 1]
def m2 = Collections.unmodifiableMap(m1)   // returns an @UnmodifiableView decorated Map

println m1.getClass() // AS EXPECTED: class java.util.LinkedHashMap
println m2.getClass() // AS EXPECTED: class java.util.Collections$UnmodifiableMap

// NOTE: plus() operations return a different class and modified data:
m2 += [m:2]
//m2 = m2 + [m:2]
println m2.getClass() // NOT AS EXPECTED: class java.util.LinkedHashMap
println m2            // NOT AS EXPECTED: [t:somestring, n:1, m:2]

// NOTE: Direct operations on the view (put, putAll, replace, remove,
// leftShift and << operator) are constrained as expected:
def m3 = Collections.unmodifiableMap(m1)
//m3.putAll([m:2])
m3 << [m:2]
// THROWS AS EXPECTED: java.lang.UnsupportedOperationException ...

With typical output like this:

2.5.14
class java.util.LinkedHashMap
class java.util.Collections$UnmodifiableMap
class java.util.LinkedHashMap
[t:somestring, n:1, m:2]
java.lang.UnsupportedOperationException
	at Script1.run(Script1.groovy:20)

For clarity, the expectation is that the "view" map m2 remains unmodifiable throughout the additions and other manipulations. I suppose that Collections$UnmodifiableMap should but does not override the plus() method in Groovy terms, but this is just an unverified educated guess based on another custom Map type I was making.