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Fix ICE with use clippy::a::b; #83336

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Mar 22, 2021
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Fix ICE with use clippy::a::b; #83336

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4 changes: 2 additions & 2 deletions compiler/rustc_resolve/src/imports.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -955,14 +955,14 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
}
return None;
}
PathResult::NonModule(path_res) if path_res.base_res() == Res::Err => {
PathResult::NonModule(_) => {
if no_ambiguity {
assert!(import.imported_module.get().is_none());
}
// The error was already reported earlier.
return None;
}
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I think it should be

            PathResult::NonModule(path_res) => {
                if no_ambiguity {
                    assert!(import.imported_module.get().is_none());
                }
                // The error was already reported earlier.
                return None;
            }

Res::Err was used to discern between reachable cases and (seemingly) unreachable cases.

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By the way, why do clippy::a and clippy::a::b seem to go through very different code paths? clippy::a didn't trigger the ICE, only clippy::a::b.

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Not sure what exactly happens there, but both imports and tool attributes are "special" in some regards.

  • Import paths are split into two parts - module (everything except for the last segment, type namespace) and the final segment resolved multiple times in all namespaces.
  • Tool attributes are also split into two parts but in a different way - the first segment resolved as a tool module, and all other segments that are not even resolved (because no definitions for them exist in source code), just automatically assumed to be a tool attribute. (Perhaps the implementation is taking a shortcut here and it could be done better, at least for diagnostics.)

When you combine these two special cases together you get some unique code paths.

PathResult::Indeterminate | PathResult::NonModule(..) => unreachable!(),
PathResult::Indeterminate => unreachable!(),
};

let (ident, target, source_bindings, target_bindings, type_ns_only) = match import.kind {
Expand Down
7 changes: 7 additions & 0 deletions src/test/ui/imports/tool-mod-child.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
use clippy::a; //~ ERROR unresolved import `clippy`
use clippy::a::b; //~ ERROR failed to resolve: maybe a missing crate `clippy`?

use rustdoc::a; //~ ERROR unresolved import `rustdoc`
use rustdoc::a::b; //~ ERROR failed to resolve: maybe a missing crate `rustdoc`?

fn main() {}
28 changes: 28 additions & 0 deletions src/test/ui/imports/tool-mod-child.stderr
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@@ -0,0 +1,28 @@
error[E0433]: failed to resolve: maybe a missing crate `clippy`?
--> $DIR/tool-mod-child.rs:2:5
|
LL | use clippy::a::b;
| ^^^^^^ maybe a missing crate `clippy`?

error[E0432]: unresolved import `clippy`
--> $DIR/tool-mod-child.rs:1:5
|
LL | use clippy::a;
| ^^^^^^ maybe a missing crate `clippy`?

error[E0433]: failed to resolve: maybe a missing crate `rustdoc`?
--> $DIR/tool-mod-child.rs:5:5
|
LL | use rustdoc::a::b;
| ^^^^^^^ maybe a missing crate `rustdoc`?

error[E0432]: unresolved import `rustdoc`
--> $DIR/tool-mod-child.rs:4:5
|
LL | use rustdoc::a;
| ^^^^^^^ maybe a missing crate `rustdoc`?

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0432, E0433.
For more information about an error, try `rustc --explain E0432`.