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Provide warning for defs that are used only in (mutual) recursion

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This patch provides errors for defs that are used only in
possibly-mutual recursion, and are not reachable outside of their
recursive closures. For example:

```
test_report!(
    mutual_recursion_not_reached_nested,
    indoc!(
        r#"
        app "test" provides [main] to "./platform"

        main =
            f = \{} -> if Bool.true then "" else g {}
            g = \{} -> if Bool.true then "" else f {}
            ""
        "#
    ),
@r###"
── DEFINITIONs ONLY USED IN RECURSION ──────────────────── /code/proj/Main.roc ─

These 2 definitions are only used in mutual recursion with themselves:

4│>      f = \{} -> if Bool.true then "" else g {}
5│>      g = \{} -> if Bool.true then "" else f {}

If you don't intend to use or export any of them, they should all be
removed!
"###
);
```
This commit is contained in:
Ayaz Hafiz 2022-12-01 18:26:01 -06:00
parent 1beb00f490
commit 0a807dc43e
No known key found for this signature in database
GPG key ID: 0E2A37416A25EF58
8 changed files with 262 additions and 15 deletions
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13
crates/compiler/can/src/module.rs
View file

@ -376,6 +376,9 @@ pub fn canonicalize_module_defs<'a>(
// See if any of the new idents we defined went unused.
// If any were unused and also not exposed, report it.
//
// We'll catch symbols that are only referenced due to (mutual) recursion later,
// when sorting the defs.
for (symbol, region) in symbols_introduced {
if !output.references.has_type_or_value_lookup(symbol)
&& !exposed_symbols.contains(&symbol)
@ -427,8 +430,14 @@ pub fn canonicalize_module_defs<'a>(
..Default::default()
};
let (mut declarations, mut output) =
crate::def::sort_can_defs_new(&mut scope, var_store, defs, new_output);
let (mut declarations, mut output) = crate::def::sort_can_defs_new(
&mut env,
&mut scope,
var_store,
defs,
new_output,
exposed_symbols,
);
debug_assert!(
output.pending_derives.is_empty(),