Describe the PR

Fix a bug in type resolution, by which expressions like a.m() have type a and not whatever the return type of m is. The fixed issues are instances of this same problem. It was not introduced in type resolution by 6.30.0, only made discoverable because UseEqualsToCompareStrings was updated to use type resolution in #2934.

This could be caused by unresolved local variables, though given how rotten the typeres code is I'm not sure. Other tests are failing now...

update

With these changes, in a call chain, the return type of method calls is now set on the PrimarySuffix that corresponds to the arguments. Previously, it was the PrimarySuffix for the method name, or the PrimaryPrefix, if the receiver is an ambiguous name (ASTName). This was inconsistent and hid the type of the receiver in that case.

Eg str.contains("") had the following type info (in the best case, whereas with the bug of #2976 the PrimaryExpression has the incorrect type string):

+ PrimaryExpression (type =  boolean)
  + PrimaryPrefix
     + Name(image = "str.contains", type = boolean)
  + PrimarySuffix
     + Arguments

where nothing hints that the receiver is of type string. Now it's

+ PrimaryExpression (type =  boolean)
  + PrimaryPrefix
     + Name(image = "str.contains", type = String)    <- this is the receiver type
  + PrimarySuffix (type = boolean)
     + Arguments

I think this is the best we can do on master. I don't want to add tests that will be thrown away when merging 7.0.x, I spent already too much time on this, so this only adds tests to the rules, not the typeres code.

Related issues

• Fixes [java] CompareObjectsWithEquals: FP with array.length #2976
• Fixes [java] CloseResource: false positive with reassignment detection #2977
• Fixes [java] UseEqualsToCompareStrings: FP with "var" variables #2979
• Fixes [java] UseEqualsToCompareStrings false positive with PMD 6.30.0 #3004

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by travis)
• Added (in-code) documentation (if needed)