NLL: Add union justifications to conflicting borrows.
Fixes#57100.
This PR adds justifications to error messages for conflicting borrows of union fields.
Where previously an error message would say ``cannot borrow `u.b` as mutable..``, it now says ``cannot borrow `u` (via `u.b`) as mutable..``.
r? @pnkfelix
use structured suggestion for method calls
Furthermore, don't suggest calling the method if it is part of a place
expression, as this is invalid syntax.
I'm thinking it might be worth putting a label on the method assignment span like "this is a method" and removing the span from the "methods are immutable" text so it isn't reported twice.
The suggestions in `src/test/ui/did_you_mean/issue-40396.stderr` are suboptimal. I could check if the containing expression is `BinOp`, but I'm not sure if that's general enough. Any ideas?
r? @estebank
This commit adds justifications to error messages for conflicting
borrows of union fields.
Where previously an error message would say
``cannot borrow `u.b` as mutable..``, it now says
``cannot borrow `u` (via `u.b`) as mutable..``.
In each of the three cases in this test, there is a mutable borrow
of some field of the union and then a shared borrow of some other field
immediately following.
Under NLL, the mutable borrow is killed straight away as it isn't
used later - therefore not causing a conflict with the shared borrow.
This commit adds a use of the first mutable borrow to force the intended
errors to appear under NLL.
Rustc explain
Fixes#48041.
To make the review easier, I separated tests update to code update. Also, I used this script to generate new ui tests stderr:
```python
from os import listdir
from os.path import isdir, isfile, join
PATH = "src/test/ui"
def do_something(path):
files = [join(path, f) for f in listdir(path)]
for f in files:
if isdir(f):
do_something(f)
continue
if not isfile(f) or not f.endswith(".stderr"):
continue
x = open(f, "r")
content = x.read().strip()
if "error[E" not in content:
continue
errors = dict()
for y in content.splitlines():
if y.startswith("error[E"):
errors[y[6:11]] = True
errors = sorted(errors.keys())
if len(errors) < 1:
print("weird... {}".format(f))
continue
if len(errors) > 1:
content += "\n\nYou've got a few errors: {}".format(", ".join(errors))
content += "\nIf you want more information on an error, try using \"rustc --explain {}\"".format(errors[0])
else:
content += "\n\nIf you want more information on this error, try using \"rustc --explain {}\"".format(errors[0])
content += "\n"
x = open(f, "w")
x.write(content)
do_something(PATH)
```
