That lawn will be a bear to maintain. - what types of construction is this?

That lawn will be a bear to maintain.

I am interested in the infinitival clause at the end there and how it relates grammatically to the rest of the sentence. Is is a complement or a modifier? Also how do we mentally reconstruct the clause at the end, which has no subject or object.

Is the sentence above related to the following types of sentence?

• This sentence is easy to read.
• It was a tough decision to make.
• The prospect was too dire to contemplate.
• The Shard took three years to build.

The lawn will be a bear to maintain.

I see this as an example of a 'hollow' infinitival clause functioning as complement to the NP "a bear". Hollow clauses derive their name from the fact that some non-subject element is missing. In this case, the object of "maintain" is missing and can be represented by gap.

Like most non-finite clauses, the infinitival clause here is subjectless, though it’s understood to be some arbitrary person(s). If we posit a plausible subject, we get:

That lawn will be a [bear (for us) to maintain __], where gap is understood as object of "maintain" and is anaphoric to "that lawn", and the square brackets enclose the NP that contains the infinitival clause.

The same principle applies to your other examples. The slightly odd one out is The prospect was too dire to contemplate, where the infinitival is licensed by "too" and hence is an 'indirect complement'. In all the other examples, the infinitival is licensed by the head of the phrase that contains it.

Note: the not very transparent term 'hollow clause' was invented by H&P in the absence of a traditional term.

It seems like a nominative, probably the subject.

To maintain that lawn (subject clause) will be (verb) a bear (predicate nominative).

The order seems to be an idiomatic sequence rather than a grammatical restructuring.