The fix is admittedly quit literally just papering over.
Long-term, I see two more principled approaches:
* we switch to a fully tree-based impl, without parse . to_string
step; with this approach, there shouldn't be any panics. The results
might be nonsensical, but so was the original input.
* we preserve the invariant that re-parsing constructed node is an
identity, and make all the `make_xxx` method return an `Option`.
closes#4044
This introduces the new type -- Semantics.
Semantics maps SyntaxNodes to various semantic info, such as type,
name resolution or macro expansions.
To do so, Semantics maintains a HashMap which maps every node it saw
to the file from which the node originated. This is enough to get all
the necessary hir bits just from syntax.
This wasn't a right decision in the first place, the feature flag was
broken in the last rustfmt release, and syntax highlighting of imports
is more important anyway
E.g. in
```
let foo = 1u32;
if true {
<|>foo;
}
```
the hover shows `()`, the type of the whole if expression, instead of the more
sensible `u32`. The reason for this was that the search for an expression was
slightly left-biased: When on the edge between two tokens, it first looked at
all ancestors of the left token and then of the right token. Instead merge the
ancestors in ascending order, so that we get the smaller of the two possible
expressions.
