Enhance Error Message For Misusing Methods As Functions

[xfoxfu]

Consider the following example (playground):

struct S;

trait T {
    fn some(&self) {}
}

impl T for S {}

fn main() {
    let s = S;

    s.some();
    s::some();
}

If there is fn some(&self);, and I called s::some() instead of s.some() (the correct one), the compiler wil emit error[E0433]: failed to resolve: use of undeclared type or module 's'. I think this is hard for developers to understand, and a hint of using method would be better in this case.

To be more precise, when the code misuses methods as functions, in addition to the current E0433, a hint would be provided, for example possible misusing methods as functions, try change to method call.

[csmoe]

error[E0433]: failed to resolve: use of undeclared type or module 's'

the error message already mentions type and module, implies what is expected here(S::some(&s)), kind of obvious I think?

[xfoxfu]

I think it would be better to provide a fix suggestion.

[estebank]

We can do what we do in other errors and lookup the identifier in the other namespaces. Implying is not enough, not everybody has the same level of familiarity with rust and what counts as obvious can depend on how caffeinated one is 😊

[nk9]

I just ran into this and spent longer than I care to mention before realizing that the (working) sample code was using CONST_VAR.encode() and my broken code was using CONST_VAR::encode().

error[E0433]: failed to resolve: use of undeclared type `URL_SAFE`
   --> get_line_image/src/main.rs:253:15
    |
  2 | use base64::{Engine as _, engine::general_purpose::URL_SAFE};
    |                           --------------------------------- help: `URL_SAFE` is defined here, but is not a type
...
253 |     let b64 = URL_SAFE::encode(b"abcdefg");
    |               ^^^^^^^^ use of undeclared type `URL_SAFE`

I think the use of undeclared type error actually sent me in the wrong direction for figuring out what was wrong. I went looking for issues with the import or the variable I was passing to the function.

In a perfect world, the compiler would check for a method on the symbol and suggest using a period instead of double colons to access it. But even if it doesn't, a more generic message could still help e.g. note: you may be trying to call a method as an associated function. Try changing to a method call (use `.`).