Implicit plus and explicit plus are non-equivalent due to binding differently

[augmentluke]

I expect the following two snippets to be equivalent:

local base = {
    a: 10,
    withADecremented:: function() self { a: super.a - 1 },
};
base { b: 20 }.withADecremented()

(implicit plus in the last line)

local base = {
    a: 10,
    withADecremented:: function() self { a: super.a - 1 },
};
base + { b: 20 }.withADecremented()

(explicit plus in the last line)

However, the first one successfully compiles to { a: 9, b: 20 } while the second fails:

RUNTIME ERROR: Field does not exist: withADecremented
	services/examples/example.jsonnet:5:8-34	$
	During evaluation

Documentation of implicit plus is scarce but the following sentence in jsonnet.org/learning/tutorial.html:

In the common case where you write foo + { ... }, i.e. the + is immediately followed by a {, then the + can be elided.

and the existence of the (no-)use-implicit-plus jsonnetfmt CLI option together suggest that foo {} is syntactic sugar for foo + {}. In fact the two appear to bind at different precedence compared to . as shown by the above example.