Adding/removing/changing infix declarations should be signalled by diff, as MAJOR change

[jvoigtlaender]

For example, assume that in the core package's Basics.elm the line

infixr 0 <|

were replaced by

infixl 0 <|

At current, elm-package diff would ignore that change. But it should actually be considered a MAJOR change under semantic versioning, because it amounts to changing the type of expressions. For example, a client of core may contain an expression like f <| g <| x. Whether or not this expression is well-typed (given some specific f, g, x) and which type it has (say, if f, g, x are unconstrained and one simply uses type inference) will change between having infixr or infixl for <|. So ignoring that change when computing the diff for core breaks the guarantees expected from semantic versioning in a big way.

[evancz]

The new implementation checks for that here, so it will count as a major change. The diffs also show the associativity and precedence as well, so you can see the change even though the name and type stays the same.