1 files changed, 291 insertions, 0 deletions

diff --git a/crates/completion/src/completions/flyimport.rs b/crates/completion/src/completions/flyimport.rs
new file mode 100644
index 000000000..222809638
--- /dev/null
+++ b/crates/completion/src/completions/flyimport.rs
@@ -0,0 +1,291 @@
+//! Feature: completion with imports-on-the-fly
+//!
+//! When completing names in the current scope, proposes additional imports from other modules or crates,
+//! if they can be qualified in the scope and their name contains all symbols from the completion input
+//! (case-insensitive, in any order or places).
+//!
+//! ```
+//! fn main() {
+//!     pda$0
+//! }
+//! # pub mod std { pub mod marker { pub struct PhantomData { } } }
+//! ```
+//! ->
+//! ```
+//! use std::marker::PhantomData;
+//!
+//! fn main() {
+//!     PhantomData
+//! }
+//! # pub mod std { pub mod marker { pub struct PhantomData { } } }
+//! ```
+//!
+//! .Fuzzy search details
+//!
+//! To avoid an excessive amount of the results returned, completion input is checked for inclusion in the names only
+//! (i.e. in `HashMap` in the `std::collections::HashMap` path).
+//! For the same reasons, avoids searching for any imports for inputs with their length less that 2 symbols.
+//!
+//! .Import configuration
+//!
+//! It is possible to configure how use-trees are merged with the `importMergeBehavior` setting.
+//! Mimics the corresponding behavior of the `Auto Import` feature.
+//!
+//! .LSP and performance implications
+//!
+//! The feature is enabled only if the LSP client supports LSP protocol version 3.16+ and reports the `additionalTextEdits`
+//! (case sensitive) resolve client capability in its client capabilities.
+//! This way the server is able to defer the costly computations, doing them for a selected completion item only.
+//! For clients with no such support, all edits have to be calculated on the completion request, including the fuzzy search completion ones,
+//! which might be slow ergo the feature is automatically disabled.
+//!
+//! .Feature toggle
+//!
+//! The feature can be forcefully turned off in the settings with the `rust-analyzer.completion.enableAutoimportCompletions` flag.
+//! Note that having this flag set to `true` does not guarantee that the feature is enabled: your client needs to have the corredponding
+//! capability enabled.
+
+use either::Either;
+use hir::{ModPath, ScopeDef};
+use ide_db::{helpers::insert_use::ImportScope, imports_locator};
+use syntax::AstNode;
+use test_utils::mark;
+
+use crate::{
+    context::CompletionContext,
+    render::{render_resolution_with_import, RenderContext},
+    ImportEdit,
+};
+
+use super::Completions;
+
+pub(crate) fn import_on_the_fly(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> {
+    if !ctx.config.enable_autoimport_completions {
+        return None;
+    }
+    if ctx.attribute_under_caret.is_some() || ctx.mod_declaration_under_caret.is_some() {
+        return None;
+    }
+    let potential_import_name = ctx.token.to_string();
+    if potential_import_name.len() < 2 {
+        return None;
+    }
+    let _p = profile::span("import_on_the_fly").detail(|| potential_import_name.to_string());
+
+    let current_module = ctx.scope.module()?;
+    let anchor = ctx.name_ref_syntax.as_ref()?;
+    let import_scope = ImportScope::find_insert_use_container(anchor.syntax(), &ctx.sema)?;
+
+    let user_input_lowercased = potential_import_name.to_lowercase();
+    let mut all_mod_paths = imports_locator::find_similar_imports(
+        &ctx.sema,
+        ctx.krate?,
+        Some(40),
+        potential_import_name,
+        true,
+        true,
+    )
+    .filter_map(|import_candidate| {
+        Some(match import_candidate {
+            Either::Left(module_def) => {
+                (current_module.find_use_path(ctx.db, module_def)?, ScopeDef::ModuleDef(module_def))
+            }
+            Either::Right(macro_def) => {
+                (current_module.find_use_path(ctx.db, macro_def)?, ScopeDef::MacroDef(macro_def))
+            }
+        })
+    })
+    .filter(|(mod_path, _)| mod_path.len() > 1)
+    .collect::<Vec<_>>();
+
+    all_mod_paths.sort_by_cached_key(|(mod_path, _)| {
+        compute_fuzzy_completion_order_key(mod_path, &user_input_lowercased)
+    });
+
+    acc.add_all(all_mod_paths.into_iter().filter_map(|(import_path, definition)| {
+        render_resolution_with_import(
+            RenderContext::new(ctx),
+            ImportEdit { import_path, import_scope: import_scope.clone() },
+            &definition,
+        )
+    }));
+    Some(())
+}
+
+fn compute_fuzzy_completion_order_key(
+    proposed_mod_path: &ModPath,
+    user_input_lowercased: &str,
+) -> usize {
+    mark::hit!(certain_fuzzy_order_test);
+    let proposed_import_name = match proposed_mod_path.segments.last() {
+        Some(name) => name.to_string().to_lowercase(),
+        None => return usize::MAX,
+    };
+    match proposed_import_name.match_indices(user_input_lowercased).next() {
+        Some((first_matching_index, _)) => first_matching_index,
+        None => usize::MAX,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::{expect, Expect};
+    use test_utils::mark;
+
+    use crate::{
+        item::CompletionKind,
+        test_utils::{check_edit, completion_list},
+    };
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let actual = completion_list(ra_fixture, CompletionKind::Magic);
+        expect.assert_eq(&actual);
+    }
+
+    #[test]
+    fn function_fuzzy_completion() {
+        check_edit(
+            "stdin",
+            r#"
+//- /lib.rs crate:dep
+pub mod io {
+    pub fn stdin() {}
+};
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    stdi$0
+}
+"#,
+            r#"
+use dep::io::stdin;
+
+fn main() {
+    stdin()$0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn macro_fuzzy_completion() {
+        check_edit(
+            "macro_with_curlies!",
+            r#"
+//- /lib.rs crate:dep
+/// Please call me as macro_with_curlies! {}
+#[macro_export]
+macro_rules! macro_with_curlies {
+    () => {}
+}
+
+//- /main.rs crate:main deps:dep
+fn main() {
+    curli$0
+}
+"#,
+            r#"
+use dep::macro_with_curlies;
+
+fn main() {
+    macro_with_curlies! {$0}
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn struct_fuzzy_completion() {
+        check_edit(
+            "ThirdStruct",
+            r#"
+//- /lib.rs crate:dep
+pub struct FirstStruct;
+pub mod some_module {
+    pub struct SecondStruct;
+    pub struct ThirdStruct;
+}
+
+//- /main.rs crate:main deps:dep
+use dep::{FirstStruct, some_module::SecondStruct};
+
+fn main() {
+    this$0
+}
+"#,
+            r#"
+use dep::{FirstStruct, some_module::{SecondStruct, ThirdStruct}};
+
+fn main() {
+    ThirdStruct
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn fuzzy_completions_come_in_specific_order() {
+        mark::check!(certain_fuzzy_order_test);
+        check(
+            r#"
+//- /lib.rs crate:dep
+pub struct FirstStruct;
+pub mod some_module {
+    // already imported, omitted
+    pub struct SecondStruct;
+    // does not contain all letters from the query, omitted
+    pub struct UnrelatedOne;
+    // contains all letters from the query, but not in sequence, displayed last
+    pub struct ThiiiiiirdStruct;
+    // contains all letters from the query, but not in the beginning, displayed second
+    pub struct AfterThirdStruct;
+    // contains all letters from the query in the begginning, displayed first
+    pub struct ThirdStruct;
+}
+
+//- /main.rs crate:main deps:dep
+use dep::{FirstStruct, some_module::SecondStruct};
+
+fn main() {
+    hir$0
+}
+"#,
+            expect![[r#"
+                st dep::some_module::ThirdStruct
+                st dep::some_module::AfterThirdStruct
+                st dep::some_module::ThiiiiiirdStruct
+            "#]],
+        );
+    }
+
+    #[test]
+    fn does_not_propose_names_in_scope() {
+        check(
+            r#"
+//- /lib.rs crate:dep
+pub mod test_mod {
+    pub trait TestTrait {
+        const SPECIAL_CONST: u8;
+        type HumbleType;
+        fn weird_function();
+        fn random_method(&self);
+    }
+    pub struct TestStruct {}
+    impl TestTrait for TestStruct {
+        const SPECIAL_CONST: u8 = 42;
+        type HumbleType = ();
+        fn weird_function() {}
+        fn random_method(&self) {}
+    }
+}
+
+//- /main.rs crate:main deps:dep
+use dep::test_mod::TestStruct;
+fn main() {
+    TestSt$0
+}
+"#,
+            expect![[r#""#]],
+        );
+    }
+}