Auto merge of #17656 - Veykril:flyimport-builtin-mod, r=Veykril

fix: Allow flyimport to import primitive shadowing modules

Fixes rust-lang/rust-analyzer#16371

Author: bors

src/tools/rust-analyzer/crates/ide-completion/src/tests/flyimport.rs

@@ -1618,3 +1618,18 @@ pub struct FooStruct;
         "#]],
     );
 }
+
+#[test]
+fn primitive_mod() {
+    check(
+        r#"
+//- minicore: str
+fn main() {
+    str::from$0
+}
+"#,
+        expect![[r#"
+            fn from_utf8_unchecked(…) (use core::str) const unsafe fn(&[u8]) -> &str
+        "#]],
+    );
+}

src/tools/rust-analyzer/crates/ide-db/src/imports/import_assets.rs

@@ -703,7 +703,7 @@ fn path_import_candidate(
 ) -> Option<ImportCandidate> {
     Some(match qualifier {
         Some(qualifier) => match sema.resolve_path(&qualifier) {
-            None => {
+            Some(PathResolution::Def(ModuleDef::BuiltinType(_))) | None => {
                 if qualifier.first_qualifier().map_or(true, |it| sema.resolve_path(&it).is_none()) {
                     let qualifier = qualifier
                         .segments()

src/tools/rust-analyzer/crates/ide/src/file_structure.rs

@@ -197,7 +197,9 @@ fn structure_token(token: SyntaxToken) -> Option<StructureNode> {
     if let Some(comment) = ast::Comment::cast(token) {
         let text = comment.text().trim();
 
-        if let Some(region_name) = text.strip_prefix("// region:").map(str::trim) {
+        if let Some(region_name) =
+            text.strip_prefix("// region:").map(str::trim).filter(|it| !it.is_empty())
+        {
             return Some(StructureNode {
                 parent: None,
                 label: region_name.to_owned(),

src/tools/rust-analyzer/crates/test-utils/src/minicore.rs

@@ -55,6 +55,7 @@
 //!     size_of: sized
 //!     sized:
 //!     slice:
+//!     str:
 //!     sync: sized
 //!     transmute:
 //!     try: infallible
@@ -1368,6 +1369,14 @@ pub mod iter {
 }
 // endregion:iterator
 
+// region:str
+pub mod str {
+    pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
+        ""
+    }
+}
+// endregion:str
+
 // region:panic
 mod panic {
     pub macro panic_2021 {