Diagnostic when "constructing" something with ::new instead of ::new() should be better.

[vi]

use std::collections::BTreeMap;

fn main() {
    let mut q = BTreeMap::new;
    for i in 0..1000_000_000 {
        q.insert(i, [0u8; 65536]);
    }
}

$ rustc heapoverflow.rs 
heapoverflow.rs:6:11: 6:34 error: no method named `insert` found for type `fn() -> collections::btree::map::BTreeMap<_, _> {collections::btree::map::BTreeMap<K, V>::new}` in the current scope
heapoverflow.rs:6         q.insert(i, [0u8; 65536]);
                            ^~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

At first I tried add instead of insert, then looked at docs, changed to insert again, then tried deliberately invalid inse3rt to ensure that error message does not change. Then I noticed fn() in error message and after little thinking found the issue.

Maybe such simple mistake should have friendlier error message? For example, if obj.method does not exist, but obj().method does, it can be mentioned somehow.

[jonas-schievink]

This is now somewhat fixed:

<anon>:6:11: 6:17 error: no method named `insert` found for type `fn() -> std::collections::BTreeMap<_, _> {<std::collections::BTreeMap<K, V>><_, _>::new}` in the current scope
<anon>:6         q.insert(i, [0u8; 65536]);
                   ^~~~~~
<anon>:6:9: 6:10 note: q is a function, perhaps you wish to call it
<anon>:6:9: 6:10 help: try calling the base function:
<anon>:          q().insert(i, [0u8; 65536]);
error: aborting due to previous error

I found "try calling the base function" to be confusing. What's a "base" function?

Another problem is that this suggests q() even when q takes arguments:

fn myfn(a: u8) { loop {} }

fn main() {
    let mut q = myfn;
    for i in 0..1000_000_000 {
        q.insert(i, [0u8; 65536]);
    }
}

<anon>:6:11: 6:17 error: no method named `insert` found for type `fn(u8) {myfn}` in the current scope
<anon>:6         q.insert(i, [0u8; 65536]);
                   ^~~~~~
<anon>:6:9: 6:10 note: q is a function, perhaps you wish to call it
<anon>:6:9: 6:10 help: try calling the base function:
<anon>:          q().insert(i, [0u8; 65536]);
error: aborting due to previous error