Address redundant errors for missing crate for nested imports and later uses of crate

compiler/rustc_resolve/src/imports.rs

@@ -217,6 +217,15 @@ impl<'ra> ImportData<'ra> {
         }
     }
 
+    /// Returns the first meaningful path segment of this import,
+    /// skipping synthetic segments like `{{root}}` and `$crate`.
+    pub(crate) fn first_non_root_segment(&self) -> Option<Symbol> {
+        self.module_path
+            .iter()
+            .find(|seg| seg.ident.name != kw::PathRoot && seg.ident.name != kw::DollarCrate)
+            .map(|seg| seg.ident.name)
+    }
+
     pub(crate) fn id(&self) -> Option<NodeId> {
         match self.kind {
             ImportKind::Single { id, .. }
@@ -653,6 +662,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
             glob_error |= import.is_glob();
 
+            if let Some(name) = import.first_non_root_segment() {
+                self.failed_import_prefixes.insert(name);
+            }
+
             if let ImportKind::Single { source, ref decls, .. } = import.kind
                 && source.name == kw::SelfLower
                 // Silence `unresolved import` error if E0429 is already emitted
@@ -1051,6 +1064,22 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     if !self.issue_145575_hack_applied {
                         assert!(import.imported_module.get().is_none());
                     }
+                    if import.is_nested() {
+                        let module = if let Some(ModuleOrUniformRoot::Module(m)) = module {
+                            m.opt_def_id()
+                        } else {
+                            None
+                        };
+                        return Some(UnresolvedImportError {
+                            span,
+                            label: Some(label),
+                            note: None,
+                            suggestion,
+                            candidates: None,
+                            segment: Some(segment_name),
+                            module,
+                        });
+                    }
                     self.report_error(
                         span,
                         ResolutionError::FailedToResolve {

compiler/rustc_resolve/src/late.rs

@@ -4424,7 +4424,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
         let Finalize { node_id, path_span, .. } = finalize;
         let report_errors = |this: &mut Self, res: Option<Res>| {
-            if this.should_report_errs() {
+            if this.should_report_errs_for_path(path) {
                 let (err, candidates) = this.smart_resolve_report_errors(
                     path,
                     None,
@@ -4558,7 +4558,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
                 let def_id = this.parent_scope.module.nearest_parent_mod();
 
-                if this.should_report_errs() {
+                if this.should_report_errs_for_path(path) {
                     if candidates.is_empty() {
                         if path.len() == 2
                             && let [segment] = prefix_path
@@ -4668,7 +4668,9 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
             Err(err) => {
                 if let Some(err) = report_errors_for_call(self, err) {
-                    self.report_error(err.span, err.node);
+                    if self.should_report_errs_for_path(path) {
+                        self.r.report_error(err.span, err.node);
+                    }
                 }
 
                 PartialRes::new(Res::Err)
@@ -4717,6 +4719,20 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             && !self.r.glob_error.is_some()
     }
 
+    /// Like `should_report_errs`, but also suppresses errors for paths whose
+    /// first segment matches a known-failed import prefix.
+    fn should_report_errs_for_path(&self, path: &[Segment]) -> bool {
+        if !self.should_report_errs() {
+            return false;
+        }
+        if let Some(first) = path.first() {
+            if self.r.failed_import_prefixes.contains(&first.ident.name) {
+                return false;
+            }
+        }
+        true
+    }
+
     // Resolve in alternative namespaces if resolution in the primary namespace fails.
     fn resolve_qpath_anywhere(
         &mut self,

compiler/rustc_resolve/src/lib.rs

@@ -1242,6 +1242,10 @@ pub struct Resolver<'ra, 'tcx> {
     glob_error: Option<ErrorGuaranteed> = None,
     visibilities_for_hashing: Vec<(LocalDefId, Visibility)> = Vec::new(),
     used_imports: FxHashSet<NodeId> = default::fx_hash_set(),
+    /// First segments of import paths that failed to resolve.
+    /// Used to suppress redundant resolution errors in late resolver
+    /// for paths sharing the same unresolved prefix.
+    failed_import_prefixes: FxHashSet<Symbol>,
     maybe_unused_trait_imports: FxIndexSet<LocalDefId>,
 
     /// Privacy errors are delayed until the end in order to deduplicate them.
@@ -1681,6 +1685,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             extern_module_map: Default::default(),
 
             glob_map: Default::default(),
+            failed_import_prefixes: FxHashSet::default(),
             maybe_unused_trait_imports: Default::default(),
 
             arenas,

tests/ui/imports/absolute-paths-in-nested-use-groups.rs

@@ -1,14 +1,10 @@
 #![allow(unused_imports)]
 
-mod foo {}
-
 use foo::{
+    //~^ ERROR: unresolved import `foo`
     ::bar,
-    //~^ ERROR: crate root in paths can only be used in start position
     super::bar,
-    //~^ ERROR: `super` in paths can only be used in start position
     self::bar,
-    //~^ ERROR: `self` in paths can only be used in start position
 };
 
 fn main() {}

tests/ui/imports/absolute-paths-in-nested-use-groups.stderr

@@ -1,21 +1,14 @@
-error[E0433]: the crate root in paths can only be used in start position
-  --> $DIR/absolute-paths-in-nested-use-groups.rs:6:5
+error[E0432]: unresolved import `foo`
+  --> $DIR/absolute-paths-in-nested-use-groups.rs:3:5
    |
-LL |     ::bar,
-   |     ^ can only be used in path start position
-
-error[E0433]: `super` in paths can only be used in start position
-  --> $DIR/absolute-paths-in-nested-use-groups.rs:8:5
+LL | use foo::{
+   |     ^^^ use of unresolved module or unlinked crate `foo`
    |
-LL |     super::bar,
-   |     ^^^^^ can only be used in path start position
-
-error[E0433]: `self` in paths can only be used in start position
-  --> $DIR/absolute-paths-in-nested-use-groups.rs:10:5
+help: you might be missing a crate named `foo`, add it to your project and import it in your code
+   |
+LL + extern crate foo;
    |
-LL |     self::bar,
-   |     ^^^^ can only be used in path start position
 
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0433`.
+For more information about this error, try `rustc --explain E0432`.

tests/ui/imports/nested-import-root-symbol-150103.rs

@@ -3,11 +3,11 @@
 // caused by `{{root}}` appearing in diagnostic suggestions
 
 mod A {
-    use Iuse::{ ::Fish }; //~ ERROR cannot find module or crate `Iuse` in the crate root
+    use Iuse::{ ::Fish }; //~ ERROR unresolved import `Iuse`
 }
 
 mod B {
-    use A::{::Fish}; //~ ERROR the crate root in paths can only be used in start position
+    use A::{::Fish}; //~ ERROR unresolved import `A::Fish`
 }
 
 fn main() {}

tests/ui/imports/nested-import-root-symbol-150103.stderr

@@ -1,4 +1,4 @@
-error[E0433]: cannot find module or crate `Iuse` in the crate root
+error[E0432]: unresolved import `Iuse`
   --> $DIR/nested-import-root-symbol-150103.rs:6:9
    |
 LL |     use Iuse::{ ::Fish };
@@ -9,12 +9,12 @@ help: you might be missing a crate named `Iuse`, add it to your project and impo
 LL + extern crate Iuse;
    |
 
-error[E0433]: the crate root in paths can only be used in start position
+error[E0432]: unresolved import `A::Fish`
   --> $DIR/nested-import-root-symbol-150103.rs:10:13
    |
 LL |     use A::{::Fish};
    |             ^ can only be used in path start position
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0433`.
+For more information about this error, try `rustc --explain E0432`.

tests/ui/imports/redundant-import-errors-nested.rs

@@ -0,0 +1,8 @@
+// Issue #153156: Too many errors for missing crate for nested imports and later uses
+
+use foo::{bar, baz::bat};
+//~^ ERROR unresolved import `foo`
+
+pub fn main() {
+    foo::qux();
+}

tests/ui/imports/redundant-import-errors-nested.stderr

@@ -0,0 +1,14 @@
+error[E0432]: unresolved import `foo`
+  --> $DIR/redundant-import-errors-nested.rs:3:5
+   |
+LL | use foo::{bar, baz::bat};
+   |     ^^^ use of unresolved module or unlinked crate `foo`
+   |
+help: you might be missing a crate named `foo`, add it to your project and import it in your code
+   |
+LL + extern crate foo;
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0432`.

tests/ui/traits/const-traits/issue-102156.rs

@@ -4,7 +4,6 @@
 
 use core::convert::{From, TryFrom};
 //~^ ERROR
-//~| ERROR
 
 use std::pin::Pin;
 use std::alloc::Allocator;

tests/ui/traits/const-traits/issue-102156.stderr

@@ -1,4 +1,4 @@
-error[E0433]: cannot find `core` in the crate root
+error[E0432]: unresolved import `core`
   --> $DIR/issue-102156.rs:5:5
    |
 LL | use core::convert::{From, TryFrom};
@@ -10,19 +10,6 @@ LL - use core::convert::{From, TryFrom};
 LL + use std::convert::{From, TryFrom};
    |
 
-error[E0433]: cannot find `core` in the crate root
-  --> $DIR/issue-102156.rs:5:5
-   |
-LL | use core::convert::{From, TryFrom};
-   |     ^^^^ you might be missing crate `core`
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: try using `std` instead of `core`
-   |
-LL - use core::convert::{From, TryFrom};
-LL + use std::convert::{From, TryFrom};
-   |
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0433`.
+For more information about this error, try `rustc --explain E0432`.

tests/ui/use/use-path-segment-kw.e2015.stderr

@@ -1027,17 +1027,6 @@ LL |         macro_dollar_crate!();
    |
    = note: this error originates in the macro `macro_dollar_crate` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0433]: `$crate` in paths can only be used in start position
-  --> $DIR/use-path-segment-kw.rs:20:27
-   |
-LL |         type A3 = foobar::$crate;
-   |                           ^^^^^^ can only be used in path start position
-...
-LL |         macro_dollar_crate!();
-   |         --------------------- in this macro invocation
-   |
-   = note: this error originates in the macro `macro_dollar_crate` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0433]: `$crate` in paths can only be used in start position
   --> $DIR/use-path-segment-kw.rs:26:26
    |
@@ -1121,12 +1110,6 @@ error[E0433]: global paths cannot start with `crate`
 LL |         type B2 = ::crate;
    |                     ^^^^^ cannot start with this
 
-error[E0433]: `crate` in paths can only be used in start position
-  --> $DIR/use-path-segment-kw.rs:106:27
-   |
-LL |         type B3 = foobar::crate;
-   |                           ^^^^^ can only be used in path start position
-
 error[E0433]: `crate` in paths can only be used in start position
   --> $DIR/use-path-segment-kw.rs:112:26
    |
@@ -1151,12 +1134,6 @@ error[E0433]: global paths cannot start with `super`
 LL |         type C2 = ::super;
    |                     ^^^^^ cannot start with this
 
-error[E0433]: `super` in paths can only be used in start position
-  --> $DIR/use-path-segment-kw.rs:144:27
-   |
-LL |         type C3 = foobar::super;
-   |                           ^^^^^ can only be used in path start position
-
 error[E0433]: `super` in paths can only be used in start position
   --> $DIR/use-path-segment-kw.rs:150:26
    |
@@ -1169,12 +1146,6 @@ error[E0433]: global paths cannot start with `self`
 LL |         type D2 = ::self;
    |                     ^^^^ cannot start with this
 
-error[E0433]: `self` in paths can only be used in start position
-  --> $DIR/use-path-segment-kw.rs:186:27
-   |
-LL |         type D3 = foobar::self;
-   |                           ^^^^ can only be used in path start position
-
 error[E0433]: `self` in paths can only be used in start position
   --> $DIR/use-path-segment-kw.rs:194:26
    |
@@ -1193,7 +1164,7 @@ error[E0433]: `self` in paths can only be used in start position
 LL |         type D6 = self::self;
    |                         ^^^^ can only be used in path start position
 
-error: aborting due to 129 previous errors
+error: aborting due to 125 previous errors
 
 Some errors have detailed explanations: E0429, E0432, E0433, E0573.
 For more information about an error, try `rustc --explain E0429`.

tests/ui/use/use-path-segment-kw.rs

@@ -17,7 +17,7 @@ macro_rules! macro_dollar_crate {
         use ::{$crate}; //~ ERROR `$crate` in paths can only be used in start position
         use ::{$crate as _nested_dollar_crate2}; //~ ERROR `$crate` in paths can only be used in start position
 
-        type A3 = foobar::$crate; //~ ERROR `$crate` in paths can only be used in start position
+        type A3 = foobar::$crate; //[e2018]~ ERROR `$crate` in paths can only be used in start position
         use foobar::$crate; //~ ERROR `$crate` in paths can only be used in start position
         use foobar::$crate as _dollar_crate3; //~ ERROR `$crate` in paths can only be used in start position
         use foobar::{$crate}; //~ ERROR `$crate` in paths can only be used in start position
@@ -103,7 +103,7 @@ mod foo {
         use ::{crate}; //~ ERROR `crate` in paths can only be used in start position
         use ::{crate as _nested_crate2}; //~ ERROR `crate` in paths can only be used in start position
 
-        type B3 = foobar::crate; //~ ERROR `crate` in paths can only be used in start position
+        type B3 = foobar::crate; //[e2018]~ ERROR `crate` in paths can only be used in start position
         use foobar::crate; //~ ERROR `crate` in paths can only be used in start position
         use foobar::crate as _crate3; //~ ERROR `crate` in paths can only be used in start position
         use foobar::{crate}; //~ ERROR `crate` in paths can only be used in start position
@@ -141,7 +141,7 @@ mod foo {
         use ::{super}; //~ ERROR `super` in paths can only be used in start position, after `self`, or after another `super`
         use ::{super as _nested_super2}; //~ ERROR `super` in paths can only be used in start position, after `self`, or after another `super`
 
-        type C3 = foobar::super; //~ ERROR `super` in paths can only be used in start position
+        type C3 = foobar::super; //[e2018]~ ERROR `super` in paths can only be used in start position
         use foobar::super; //~ ERROR `super` in paths can only be used in start position, after `self`, or after another `super`
         use foobar::super as _super3; //~ ERROR `super` in paths can only be used in start position, after `self`, or after another `super`
         use foobar::{super}; //~ ERROR `super` in paths can only be used in start position, after `self`, or after another `super`
@@ -183,7 +183,7 @@ mod foo {
         //[e2015]~^ ERROR imports need to be explicitly named
         pub use ::{self as _nested_self2}; //[e2018]~ ERROR extern prelude cannot be imported
 
-        type D3 = foobar::self; //~ ERROR `self` in paths can only be used in start position
+        type D3 = foobar::self; //[e2018]~ ERROR `self` in paths can only be used in start position
         pub use foobar::qux::self; //~ ERROR `self` imports are only allowed within a { } list
         //[e2015]~^ ERROR unresolved import `foobar`
         pub use foobar::self as _self3; //~ ERROR `self` imports are only allowed within a { } list

tests/ui/use/use-super-global-path.rs

@@ -5,8 +5,7 @@ struct Z;
 
 mod foo {
     use ::super::{S, Z};
-    //~^ ERROR: global paths cannot start with `super`
-    //~| ERROR: global paths cannot start with `super`
+    //~^ ERROR: unresolved import `super`
 
     pub fn g() {
         use ::super::main; //~ ERROR: global paths cannot start with `super`