Query Language: Allow Infix & Prefix input formats & determine normalized query format

[GerkinDev]

In its final form, the query language should allow a wide variety of combinations, to makes queries as easy to write as they are to think. Diaspora should perform following query-to-assertion translations:

• { "foo": { "==" { "bar": 2 }}} => entity.foo == {bar: 2}
• { "foo": { "bar": 2, "baz": 3 }} => entity.foo.bar == 2 && entity.foo.baz == 3
• { "foo" { "$contains": { "bar": 2, "baz": 3 }}} => entity.foo.bar == 2 && entity.foo.baz == 3
• { "==": { "foo": 1 }} => entity.foo == 1
• { "foo": { "||" [ 1, 2 ]}} => entity.foo == 1 || entity.foo == 2
• { "foo": { "||": [ 1, 2, 3 ] }, "bar": { ">": 1 }} => (entity.foo == 1 || entity.foo == 2 || entity.foo == 3) && entity.bar > 1
• { "||": [{ "foo": { "==": 1 }}, { "bar"; { "==" 2 }}]} => entity.foo == 1 || entity.bar == 2

Rules are that several operator properties are implicitly resolved as &&, and implicit { [field]: value} without operator will have different results depending on the type of the value.

• If its a primitive, it will be resolved as { "==": { [field]: value }}
• If its an object, it will be resolved as { "$contains": { [field]: value}}

We've seen with @IkarosWilo that operators at root set a "prefix" mode.
If it's a field name, the "infix" mode is enabled: it projects its left operand in a new operator child object.

About escaping

We have to support the case where a field is named the same way as an operator, like $equal or ||. Escaping query keys may be done with ., this way: { ".$equal": { ">": 1}}. The leading dot forces the key to be treated as a field name instead of an operator, and is removed in the resulting query.

To output a leading dot in the output query, 2 dots should be used: { "..$equal": { ">": 1}}

About fields relation

It may be relevant to support in-entity fields comparisons, like this assert: entity.a == entity.b. But how to mark the value as a field instead of a string ?