Provide a better error when code is put outside of a function #92615
Description
Examples in the documentation often provide excerpts instead of full programs. A beginner might try compiling that code directly, and be confused that it doesn't work. Currently, the error messages for that case don't provide any hints as to what might be wrong:
error: expected item, found keyword `let`
--> src/lib.rs:1:1
|
1 | let data = [4, 8, 15, 16, 23, 42];
| ^^^ expected item
error: expected one of `!` or `::`, found `(`
--> src/lib.rs:2:10
|
2 | fs::write("foo.txt", "Hello!").unwrap();
| ^ expected one of `!` or `::`
error: macro expansion ignores token `{` and any following
|
::: src/lib.rs:1:1
|
1 | println!("Hello, world!");
| ------------------------- caused by the macro expansion here
|
= note: the usage of `println!` is likely invalid in item context
Ideally the output should look like:
error: `let` is invalid outside of a function
--> src/lib.rs:1:1
|
1 | let data = [4, 8, 15, 16, 23, 42];
| ^^^ not valid outside of a function
help: put your code in a `main` function:
| fn main() {
| let data = [4, 8, 15, 16, 23, 42];
| for n in data {
| dbg!(n);
| }
| }