Split parts of `ide_db::call_info` off into `ide`

9 files changed, 765 insertions, 752 deletions

diff --git a/crates/ide/src/call_info.rs b/crates/ide/src/call_info.rs
new file mode 100644
index 00000000000..7568faa6bd5
--- /dev/null
+++ b/crates/ide/src/call_info.rs
@@ -0,0 +1,679 @@
+//! This module provides primitives for tracking the information about a call site.
+
+use either::Either;
+use hir::{HasAttrs, HirDisplay, Semantics};
+use ide_db::{active_parameter::callable_for_token, base_db::FilePosition};
+use stdx::format_to;
+use syntax::{algo, AstNode, Direction, TextRange, TextSize};
+
+use crate::RootDatabase;
+
+/// Contains information about a call site. Specifically the
+/// `FunctionSignature`and current parameter.
+#[derive(Debug)]
+pub struct CallInfo {
+    pub doc: Option<String>,
+    pub signature: String,
+    pub active_parameter: Option<usize>,
+    parameters: Vec<TextRange>,
+}
+
+impl CallInfo {
+    pub fn parameter_labels(&self) -> impl Iterator<Item = &str> + '_ {
+        self.parameters.iter().map(move |&it| &self.signature[it])
+    }
+
+    pub fn parameter_ranges(&self) -> &[TextRange] {
+        &self.parameters
+    }
+
+    fn push_param(&mut self, param: &str) {
+        if !self.signature.ends_with('(') {
+            self.signature.push_str(", ");
+        }
+        let start = TextSize::of(&self.signature);
+        self.signature.push_str(param);
+        let end = TextSize::of(&self.signature);
+        self.parameters.push(TextRange::new(start, end))
+    }
+}
+
+/// Computes parameter information for the given call expression.
+pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<CallInfo> {
+    let sema = Semantics::new(db);
+    let file = sema.parse(position.file_id);
+    let file = file.syntax();
+    let token = file
+        .token_at_offset(position.offset)
+        .left_biased()
+        // if the cursor is sandwiched between two space tokens and the call is unclosed
+        // this prevents us from leaving the CallExpression
+        .and_then(|tok| algo::skip_trivia_token(tok, Direction::Prev))?;
+    let token = sema.descend_into_macros_single(token);
+
+    let (callable, active_parameter) = callable_for_token(&sema, token)?;
+
+    let mut res =
+        CallInfo { doc: None, signature: String::new(), parameters: vec![], active_parameter };
+
+    match callable.kind() {
+        hir::CallableKind::Function(func) => {
+            res.doc = func.docs(db).map(|it| it.into());
+            format_to!(res.signature, "fn {}", func.name(db));
+        }
+        hir::CallableKind::TupleStruct(strukt) => {
+            res.doc = strukt.docs(db).map(|it| it.into());
+            format_to!(res.signature, "struct {}", strukt.name(db));
+        }
+        hir::CallableKind::TupleEnumVariant(variant) => {
+            res.doc = variant.docs(db).map(|it| it.into());
+            format_to!(
+                res.signature,
+                "enum {}::{}",
+                variant.parent_enum(db).name(db),
+                variant.name(db)
+            );
+        }
+        hir::CallableKind::Closure => (),
+    }
+
+    res.signature.push('(');
+    {
+        if let Some(self_param) = callable.receiver_param(db) {
+            format_to!(res.signature, "{}", self_param)
+        }
+        let mut buf = String::new();
+        for (pat, ty) in callable.params(db) {
+            buf.clear();
+            if let Some(pat) = pat {
+                match pat {
+                    Either::Left(_self) => format_to!(buf, "self: "),
+                    Either::Right(pat) => format_to!(buf, "{}: ", pat),
+                }
+            }
+            format_to!(buf, "{}", ty.display(db));
+            res.push_param(&buf);
+        }
+    }
+    res.signature.push(')');
+
+    match callable.kind() {
+        hir::CallableKind::Function(_) | hir::CallableKind::Closure => {
+            let ret_type = callable.return_type();
+            if !ret_type.is_unit() {
+                format_to!(res.signature, " -> {}", ret_type.display(db));
+            }
+        }
+        hir::CallableKind::TupleStruct(_) | hir::CallableKind::TupleEnumVariant(_) => {}
+    }
+    Some(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::{expect, Expect};
+    use ide_db::base_db::{fixture::ChangeFixture, FilePosition};
+
+    use crate::RootDatabase;
+
+    /// Creates analysis from a multi-file fixture, returns positions marked with $0.
+    pub(crate) fn position(ra_fixture: &str) -> (RootDatabase, FilePosition) {
+        let change_fixture = ChangeFixture::parse(ra_fixture);
+        let mut database = RootDatabase::default();
+        database.apply_change(change_fixture.change);
+        let (file_id, range_or_offset) =
+            change_fixture.file_position.expect("expected a marker ($0)");
+        let offset = range_or_offset.expect_offset();
+        (database, FilePosition { file_id, offset })
+    }
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let (db, position) = position(ra_fixture);
+        let call_info = crate::call_info::call_info(&db, position);
+        let actual = match call_info {
+            Some(call_info) => {
+                let docs = match &call_info.doc {
+                    None => "".to_string(),
+                    Some(docs) => format!("{}\n------\n", docs.as_str()),
+                };
+                let params = call_info
+                    .parameter_labels()
+                    .enumerate()
+                    .map(|(i, param)| {
+                        if Some(i) == call_info.active_parameter {
+                            format!("<{}>", param)
+                        } else {
+                            param.to_string()
+                        }
+                    })
+                    .collect::<Vec<_>>()
+                    .join(", ");
+                format!("{}{}\n({})\n", docs, call_info.signature, params)
+            }
+            None => String::new(),
+        };
+        expect.assert_eq(&actual);
+    }
+
+    #[test]
+    fn test_fn_signature_two_args() {
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo($03, ); }
+"#,
+            expect![[r#"
+                fn foo(x: u32, y: u32) -> u32
+                (<x: u32>, y: u32)
+            "#]],
+        );
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo(3$0, ); }
+"#,
+            expect![[r#"
+                fn foo(x: u32, y: u32) -> u32
+                (<x: u32>, y: u32)
+            "#]],
+        );
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo(3,$0 ); }
+"#,
+            expect![[r#"
+                fn foo(x: u32, y: u32) -> u32
+                (x: u32, <y: u32>)
+            "#]],
+        );
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo(3, $0); }
+"#,
+            expect![[r#"
+                fn foo(x: u32, y: u32) -> u32
+                (x: u32, <y: u32>)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_two_args_empty() {
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo($0); }
+"#,
+            expect![[r#"
+                fn foo(x: u32, y: u32) -> u32
+                (<x: u32>, y: u32)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_two_args_first_generics() {
+        check(
+            r#"
+fn foo<T, U: Copy + Display>(x: T, y: U) -> u32
+    where T: Copy + Display, U: Debug
+{ x + y }
+
+fn bar() { foo($03, ); }
+"#,
+            expect![[r#"
+                fn foo(x: i32, y: {unknown}) -> u32
+                (<x: i32>, y: {unknown})
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_no_params() {
+        check(
+            r#"
+fn foo<T>() -> T where T: Copy + Display {}
+fn bar() { foo($0); }
+"#,
+            expect![[r#"
+                fn foo() -> {unknown}
+                ()
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_for_impl() {
+        check(
+            r#"
+struct F;
+impl F { pub fn new() { } }
+fn bar() {
+    let _ : F = F::new($0);
+}
+"#,
+            expect![[r#"
+                fn new()
+                ()
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_for_method_self() {
+        check(
+            r#"
+struct S;
+impl S { pub fn do_it(&self) {} }
+
+fn bar() {
+    let s: S = S;
+    s.do_it($0);
+}
+"#,
+            expect![[r#"
+                fn do_it(&self)
+                ()
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_for_method_with_arg() {
+        check(
+            r#"
+struct S;
+impl S {
+    fn foo(&self, x: i32) {}
+}
+
+fn main() { S.foo($0); }
+"#,
+            expect![[r#"
+                fn foo(&self, x: i32)
+                (<x: i32>)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_for_generic_method() {
+        check(
+            r#"
+struct S<T>(T);
+impl<T> S<T> {
+    fn foo(&self, x: T) {}
+}
+
+fn main() { S(1u32).foo($0); }
+"#,
+            expect![[r#"
+                fn foo(&self, x: u32)
+                (<x: u32>)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_for_method_with_arg_as_assoc_fn() {
+        check(
+            r#"
+struct S;
+impl S {
+    fn foo(&self, x: i32) {}
+}
+
+fn main() { S::foo($0); }
+"#,
+            expect![[r#"
+                fn foo(self: &S, x: i32)
+                (<self: &S>, x: i32)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_with_docs_simple() {
+        check(
+            r#"
+/// test
+// non-doc-comment
+fn foo(j: u32) -> u32 {
+    j
+}
+
+fn bar() {
+    let _ = foo($0);
+}
+"#,
+            expect![[r#"
+            test
+            ------
+            fn foo(j: u32) -> u32
+            (<j: u32>)
+        "#]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_with_docs() {
+        check(
+            r#"
+/// Adds one to the number given.
+///
+/// # Examples
+///
+/// ```
+/// let five = 5;
+///
+/// assert_eq!(6, my_crate::add_one(5));
+/// ```
+pub fn add_one(x: i32) -> i32 {
+    x + 1
+}
+
+pub fn do() {
+    add_one($0
+}"#,
+            expect![[r##"
+            Adds one to the number given.
+
+            # Examples
+
+            ```
+            let five = 5;
+
+            assert_eq!(6, my_crate::add_one(5));
+            ```
+            ------
+            fn add_one(x: i32) -> i32
+            (<x: i32>)
+        "##]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_with_docs_impl() {
+        check(
+            r#"
+struct addr;
+impl addr {
+    /// Adds one to the number given.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let five = 5;
+    ///
+    /// assert_eq!(6, my_crate::add_one(5));
+    /// ```
+    pub fn add_one(x: i32) -> i32 {
+        x + 1
+    }
+}
+
+pub fn do_it() {
+    addr {};
+    addr::add_one($0);
+}
+"#,
+            expect![[r##"
+            Adds one to the number given.
+
+            # Examples
+
+            ```
+            let five = 5;
+
+            assert_eq!(6, my_crate::add_one(5));
+            ```
+            ------
+            fn add_one(x: i32) -> i32
+            (<x: i32>)
+        "##]],
+        );
+    }
+
+    #[test]
+    fn test_fn_signature_with_docs_from_actix() {
+        check(
+            r#"
+struct WriteHandler<E>;
+
+impl<E> WriteHandler<E> {
+    /// Method is called when writer emits error.
+    ///
+    /// If this method returns `ErrorAction::Continue` writer processing
+    /// continues otherwise stream processing stops.
+    fn error(&mut self, err: E, ctx: &mut Self::Context) -> Running {
+        Running::Stop
+    }
+
+    /// Method is called when writer finishes.
+    ///
+    /// By default this method stops actor's `Context`.
+    fn finished(&mut self, ctx: &mut Self::Context) {
+        ctx.stop()
+    }
+}
+
+pub fn foo(mut r: WriteHandler<()>) {
+    r.finished($0);
+}
+"#,
+            expect![[r#"
+            Method is called when writer finishes.
+
+            By default this method stops actor's `Context`.
+            ------
+            fn finished(&mut self, ctx: &mut {unknown})
+            (<ctx: &mut {unknown}>)
+        "#]],
+        );
+    }
+
+    #[test]
+    fn call_info_bad_offset() {
+        check(
+            r#"
+fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo $0 (3, ); }
+"#,
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn test_nested_method_in_lambda() {
+        check(
+            r#"
+struct Foo;
+impl Foo { fn bar(&self, _: u32) { } }
+
+fn bar(_: u32) { }
+
+fn main() {
+    let foo = Foo;
+    std::thread::spawn(move || foo.bar($0));
+}
+"#,
+            expect![[r#"
+                fn bar(&self, _: u32)
+                (<_: u32>)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn works_for_tuple_structs() {
+        check(
+            r#"
+/// A cool tuple struct
+struct S(u32, i32);
+fn main() {
+    let s = S(0, $0);
+}
+"#,
+            expect![[r#"
+            A cool tuple struct
+            ------
+            struct S(u32, i32)
+            (u32, <i32>)
+        "#]],
+        );
+    }
+
+    #[test]
+    fn generic_struct() {
+        check(
+            r#"
+struct S<T>(T);
+fn main() {
+    let s = S($0);
+}
+"#,
+            expect![[r#"
+                struct S({unknown})
+                (<{unknown}>)
+            "#]],
+        );
+    }
+
+    #[test]
+    fn works_for_enum_variants() {
+        check(
+            r#"
+enum E {
+    /// A Variant
+    A(i32),
+    /// Another
+    B,
+    /// And C
+    C { a: i32, b: i32 }
+}
+
+fn main() {
+    let a = E::A($0);
+}
+"#,
+            expect![[r#"
+            A Variant
+            ------
+            enum E::A(i32)
+            (<i32>)
+        "#]],
+        );
+    }
+
+    #[test]
+    fn cant_call_struct_record() {
+        check(
+            r#"
+struct S { x: u32, y: i32 }
+fn main() {
+    let s = S($0);
+}
+"#,
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn cant_call_enum_record() {
+        check(
+            r#"
+enum E {
+    /// A Variant
+    A(i32),
+    /// Another
+    B,
+    /// And C
+    C { a: i32, b: i32 }
+}
+
+fn main() {
+    let a = E::C($0);
+}
+"#,
+            expect![[""]],
+        );
+    }
+
+    #[test]
+    fn fn_signature_for_call_in_macro() {
+        check(
+            r#"
+macro_rules! id { ($($tt:tt)*) => { $($tt)* } }
+fn foo() { }
+id! {
+    fn bar() { foo($0); }
+}
+"#,
+            expect![[r#"
+                fn foo()
+                ()
+            "#]],
+        );
+    }
+
+    #[test]
+    fn call_info_for_lambdas() {
+        check(
+            r#"
+struct S;
+fn foo(s: S) -> i32 { 92 }
+fn main() {
+    (|s| foo(s))($0)
+}
+        "#,
+            expect![[r#"
+                (S) -> i32
+                (<S>)
+            "#]],
+        )
+    }
+
+    #[test]
+    fn call_info_for_fn_ptr() {
+        check(
+            r#"
+fn main(f: fn(i32, f64) -> char) {
+    f(0, $0)
+}
+        "#,
+            expect![[r#"
+                (i32, f64) -> char
+                (i32, <f64>)
+            "#]],
+        )
+    }
+
+    #[test]
+    fn call_info_for_unclosed_call() {
+        check(
+            r#"
+fn foo(foo: u32, bar: u32) {}
+fn main() {
+    foo($0
+}"#,
+            expect![[r#"
+            fn foo(foo: u32, bar: u32)
+            (<foo: u32>, bar: u32)
+        "#]],
+        );
+        // check with surrounding space
+        check(
+            r#"
+fn foo(foo: u32, bar: u32) {}
+fn main() {
+    foo( $0
+}"#,
+            expect![[r#"
+            fn foo(foo: u32, bar: u32)
+            (<foo: u32>, bar: u32)
+        "#]],
+        )
+    }
+}
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index df26869dba6..034a5117933 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -24,6 +24,7 @@ mod navigation_target;
 
 mod annotations;
 mod call_hierarchy;
+mod call_info;
 mod doc_links;
 mod highlight_related;
 mod expand_macro;
@@ -73,6 +74,7 @@ use crate::navigation_target::{ToNav, TryToNav};
 pub use crate::{
     annotations::{Annotation, AnnotationConfig, AnnotationKind},
     call_hierarchy::CallItem,
+    call_info::CallInfo,
     expand_macro::ExpandedMacro,
     file_structure::{StructureNode, StructureNodeKind},
     folding_ranges::{Fold, FoldKind},
@@ -106,7 +108,6 @@ pub use ide_db::{
         Cancelled, Change, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange,
         SourceRoot, SourceRootId,
     },
-    call_info::CallInfo,
     label::Label,
     line_index::{LineCol, LineColUtf16, LineIndex},
     search::{ReferenceCategory, SearchScope},
@@ -434,7 +435,7 @@ impl Analysis {
 
     /// Computes parameter information for the given call expression.
     pub fn call_info(&self, position: FilePosition) -> Cancellable<Option<CallInfo>> {
-        self.with_db(|db| ide_db::call_info::call_info(db, position))
+        self.with_db(|db| call_info::call_info(db, position))
     }
 
     /// Computes call hierarchy candidates for the given file position.
diff --git a/crates/ide/src/static_index.rs b/crates/ide/src/static_index.rs
index e09683f6890..29eef546cef 100644
--- a/crates/ide/src/static_index.rs
+++ b/crates/ide/src/static_index.rs
@@ -3,18 +3,18 @@
 
 use std::collections::HashMap;
 
-use hir::Semantics;
-use hir::{db::HirDatabase, Crate, Module};
-use ide_db::base_db::{FileId, FileRange, SourceDatabaseExt};
-use ide_db::defs::Definition;
-use ide_db::RootDatabase;
+use hir::{db::HirDatabase, Crate, Module, Semantics};
+use ide_db::{
+    base_db::{FileId, FileRange, SourceDatabaseExt},
+    defs::Definition,
+    RootDatabase,
+};
 use rustc_hash::FxHashSet;
-use syntax::{AstNode, SyntaxKind::*, T};
-use syntax::{SyntaxToken, TextRange};
+use syntax::{AstNode, SyntaxKind::*, SyntaxToken, TextRange, T};
 
-use crate::hover::hover_for_definition;
 use crate::{
-    Analysis, Fold, HoverConfig, HoverDocFormat, HoverResult, InlayHint, InlayHintsConfig, TryToNav,
+    hover::hover_for_definition, Analysis, Fold, HoverConfig, HoverDocFormat, HoverResult,
+    InlayHint, InlayHintsConfig, TryToNav,
 };
 
 /// A static representation of fully analyzed source code.
diff --git a/crates/ide/src/syntax_highlighting/inject.rs b/crates/ide/src/syntax_highlighting/inject.rs
index b7a3fb62cb4..543a7884825 100644
--- a/crates/ide/src/syntax_highlighting/inject.rs
+++ b/crates/ide/src/syntax_highlighting/inject.rs
@@ -5,7 +5,8 @@ use std::mem;
 use either::Either;
 use hir::{InFile, Semantics};
 use ide_db::{
-    call_info::ActiveParameter, defs::Definition, helpers::rust_doc::is_rust_fence, SymbolKind,
+    active_parameter::ActiveParameter, defs::Definition, helpers::rust_doc::is_rust_fence,
+    SymbolKind,
 };
 use syntax::{
     ast::{self, AstNode, IsString},
diff --git a/crates/ide_completion/src/context.rs b/crates/ide_completion/src/context.rs
index 8759e2d108c..d9ddd9f2aeb 100644
--- a/crates/ide_completion/src/context.rs
+++ b/crates/ide_completion/src/context.rs
@@ -3,8 +3,8 @@
 use base_db::SourceDatabaseExt;
 use hir::{Local, Name, ScopeDef, Semantics, SemanticsScope, Type, TypeInfo};
 use ide_db::{
+    active_parameter::ActiveParameter,
     base_db::{FilePosition, SourceDatabase},
-    call_info::ActiveParameter,
     RootDatabase,
 };
 use syntax::{
diff --git a/crates/ide_db/src/active_parameter.rs b/crates/ide_db/src/active_parameter.rs
new file mode 100644
index 00000000000..47bd7aa9798
--- /dev/null
+++ b/crates/ide_db/src/active_parameter.rs
@@ -0,0 +1,70 @@
+//! This module provides functionality for querying callable information about a token.
+
+use either::Either;
+use hir::{Semantics, Type};
+use syntax::{
+    ast::{self, HasArgList, HasName},
+    AstNode, SyntaxToken,
+};
+
+use crate::RootDatabase;
+
+#[derive(Debug)]
+pub struct ActiveParameter {
+    pub ty: Type,
+    pub pat: Either<ast::SelfParam, ast::Pat>,
+}
+
+impl ActiveParameter {
+    /// Returns information about the call argument this token is part of.
+    pub fn at_token(sema: &Semantics<RootDatabase>, token: SyntaxToken) -> Option<Self> {
+        let (signature, active_parameter) = callable_for_token(sema, token)?;
+
+        let idx = active_parameter?;
+        let mut params = signature.params(sema.db);
+        if !(idx < params.len()) {
+            cov_mark::hit!(too_many_arguments);
+            return None;
+        }
+        let (pat, ty) = params.swap_remove(idx);
+        pat.map(|pat| ActiveParameter { ty, pat })
+    }
+
+    pub fn ident(&self) -> Option<ast::Name> {
+        self.pat.as_ref().right().and_then(|param| match param {
+            ast::Pat::IdentPat(ident) => ident.name(),
+            _ => None,
+        })
+    }
+}
+
+/// Returns a [`hir::Callable`] this token is a part of and its argument index of said callable.
+pub fn callable_for_token(
+    sema: &Semantics<RootDatabase>,
+    token: SyntaxToken,
+) -> Option<(hir::Callable, Option<usize>)> {
+    // Find the calling expression and it's NameRef
+    let parent = token.parent()?;
+    let calling_node = parent.ancestors().filter_map(ast::CallableExpr::cast).find(|it| {
+        it.arg_list()
+            .map_or(false, |it| it.syntax().text_range().contains(token.text_range().start()))
+    })?;
+
+    let callable = match &calling_node {
+        ast::CallableExpr::Call(call) => {
+            let expr = call.expr()?;
+            sema.type_of_expr(&expr)?.adjusted().as_callable(sema.db)
+        }
+        ast::CallableExpr::MethodCall(call) => sema.resolve_method_call_as_callable(call),
+    }?;
+    let active_param = if let Some(arg_list) = calling_node.arg_list() {
+        let param = arg_list
+            .args()
+            .take_while(|arg| arg.syntax().text_range().end() <= token.text_range().start())
+            .count();
+        Some(param)
+    } else {
+        None
+    };
+    Some((callable, active_param))
+}
diff --git a/crates/ide_db/src/call_info.rs b/crates/ide_db/src/call_info.rs
deleted file mode 100644
index 9e15702c5fb..00000000000
--- a/crates/ide_db/src/call_info.rs
+++ /dev/null
@@ -1,174 +0,0 @@
-//! This crate provides primitives for tracking the information about a call site.
-use base_db::FilePosition;
-use either::Either;
-use hir::{HasAttrs, HirDisplay, Semantics, Type};
-use stdx::format_to;
-use syntax::{
-    algo,
-    ast::{self, HasArgList, HasName},
-    AstNode, Direction, SyntaxToken, TextRange, TextSize,
-};
-
-use crate::RootDatabase;
-
-/// Contains information about a call site. Specifically the
-/// `FunctionSignature`and current parameter.
-#[derive(Debug)]
-pub struct CallInfo {
-    pub doc: Option<String>,
-    pub signature: String,
-    pub active_parameter: Option<usize>,
-    parameters: Vec<TextRange>,
-}
-
-impl CallInfo {
-    pub fn parameter_labels(&self) -> impl Iterator<Item = &str> + '_ {
-        self.parameters.iter().map(move |&it| &self.signature[it])
-    }
-
-    pub fn parameter_ranges(&self) -> &[TextRange] {
-        &self.parameters
-    }
-
-    fn push_param(&mut self, param: &str) {
-        if !self.signature.ends_with('(') {
-            self.signature.push_str(", ");
-        }
-        let start = TextSize::of(&self.signature);
-        self.signature.push_str(param);
-        let end = TextSize::of(&self.signature);
-        self.parameters.push(TextRange::new(start, end))
-    }
-}
-
-/// Computes parameter information for the given call expression.
-pub fn call_info(db: &RootDatabase, position: FilePosition) -> Option<CallInfo> {
-    let sema = Semantics::new(db);
-    let file = sema.parse(position.file_id);
-    let file = file.syntax();
-    let token = file
-        .token_at_offset(position.offset)
-        .left_biased()
-        // if the cursor is sandwiched between two space tokens and the call is unclosed
-        // this prevents us from leaving the CallExpression
-        .and_then(|tok| algo::skip_trivia_token(tok, Direction::Prev))?;
-    let token = sema.descend_into_macros_single(token);
-
-    let (callable, active_parameter) = call_info_impl(&sema, token)?;
-
-    let mut res =
-        CallInfo { doc: None, signature: String::new(), parameters: vec![], active_parameter };
-
-    match callable.kind() {
-        hir::CallableKind::Function(func) => {
-            res.doc = func.docs(db).map(|it| it.into());
-            format_to!(res.signature, "fn {}", func.name(db));
-        }
-        hir::CallableKind::TupleStruct(strukt) => {
-            res.doc = strukt.docs(db).map(|it| it.into());
-            format_to!(res.signature, "struct {}", strukt.name(db));
-        }
-        hir::CallableKind::TupleEnumVariant(variant) => {
-            res.doc = variant.docs(db).map(|it| it.into());
-            format_to!(
-                res.signature,
-                "enum {}::{}",
-                variant.parent_enum(db).name(db),
-                variant.name(db)
-            );
-        }
-        hir::CallableKind::Closure => (),
-    }
-
-    res.signature.push('(');
-    {
-        if let Some(self_param) = callable.receiver_param(db) {
-            format_to!(res.signature, "{}", self_param)
-        }
-        let mut buf = String::new();
-        for (pat, ty) in callable.params(db) {
-            buf.clear();
-            if let Some(pat) = pat {
-                match pat {
-                    Either::Left(_self) => format_to!(buf, "self: "),
-                    Either::Right(pat) => format_to!(buf, "{}: ", pat),
-                }
-            }
-            format_to!(buf, "{}", ty.display(db));
-            res.push_param(&buf);
-        }
-    }
-    res.signature.push(')');
-
-    match callable.kind() {
-        hir::CallableKind::Function(_) | hir::CallableKind::Closure => {
-            let ret_type = callable.return_type();
-            if !ret_type.is_unit() {
-                format_to!(res.signature, " -> {}", ret_type.display(db));
-            }
-        }
-        hir::CallableKind::TupleStruct(_) | hir::CallableKind::TupleEnumVariant(_) => {}
-    }
-    Some(res)
-}
-
-fn call_info_impl(
-    sema: &Semantics<RootDatabase>,
-    token: SyntaxToken,
-) -> Option<(hir::Callable, Option<usize>)> {
-    // Find the calling expression and it's NameRef
-    let parent = token.parent()?;
-    let calling_node = parent.ancestors().filter_map(ast::CallableExpr::cast).find(|it| {
-        it.arg_list()
-            .map_or(false, |it| it.syntax().text_range().contains(token.text_range().start()))
-    })?;
-
-    let callable = match &calling_node {
-        ast::CallableExpr::Call(call) => {
-            let expr = call.expr()?;
-            sema.type_of_expr(&expr)?.adjusted().as_callable(sema.db)
-        }
-        ast::CallableExpr::MethodCall(call) => sema.resolve_method_call_as_callable(call),
-    }?;
-    let active_param = if let Some(arg_list) = calling_node.arg_list() {
-        let param = arg_list
-            .args()
-            .take_while(|arg| arg.syntax().text_range().end() <= token.text_range().start())
-            .count();
-        Some(param)
-    } else {
-        None
-    };
-    Some((callable, active_param))
-}
-
-#[derive(Debug)]
-pub struct ActiveParameter {
-    pub ty: Type,
-    pub pat: Either<ast::SelfParam, ast::Pat>,
-}
-
-impl ActiveParameter {
-    pub fn at_token(sema: &Semantics<RootDatabase>, token: SyntaxToken) -> Option<Self> {
-        let (signature, active_parameter) = call_info_impl(sema, token)?;
-
-        let idx = active_parameter?;
-        let mut params = signature.params(sema.db);
-        if !(idx < params.len()) {
-            cov_mark::hit!(too_many_arguments);
-            return None;
-        }
-        let (pat, ty) = params.swap_remove(idx);
-        pat.map(|pat| ActiveParameter { ty, pat })
-    }
-
-    pub fn ident(&self) -> Option<ast::Name> {
-        self.pat.as_ref().right().and_then(|param| match param {
-            ast::Pat::IdentPat(ident) => ident.name(),
-            _ => None,
-        })
-    }
-}
-
-#[cfg(test)]
-mod tests;
diff --git a/crates/ide_db/src/call_info/tests.rs b/crates/ide_db/src/call_info/tests.rs
deleted file mode 100644
index 8cdfcd027a3..00000000000
--- a/crates/ide_db/src/call_info/tests.rs
+++ /dev/null
@@ -1,564 +0,0 @@
-use base_db::{fixture::ChangeFixture, FilePosition};
-use expect_test::{expect, Expect};
-
-use crate::RootDatabase;
-
-/// Creates analysis from a multi-file fixture, returns positions marked with $0.
-pub(crate) fn position(ra_fixture: &str) -> (RootDatabase, FilePosition) {
-    let change_fixture = ChangeFixture::parse(ra_fixture);
-    let mut database = RootDatabase::default();
-    database.apply_change(change_fixture.change);
-    let (file_id, range_or_offset) = change_fixture.file_position.expect("expected a marker ($0)");
-    let offset = range_or_offset.expect_offset();
-    (database, FilePosition { file_id, offset })
-}
-
-fn check(ra_fixture: &str, expect: Expect) {
-    let (db, position) = position(ra_fixture);
-    let call_info = crate::call_info::call_info(&db, position);
-    let actual = match call_info {
-        Some(call_info) => {
-            let docs = match &call_info.doc {
-                None => "".to_string(),
-                Some(docs) => format!("{}\n------\n", docs.as_str()),
-            };
-            let params = call_info
-                .parameter_labels()
-                .enumerate()
-                .map(|(i, param)| {
-                    if Some(i) == call_info.active_parameter {
-                        format!("<{}>", param)
-                    } else {
-                        param.to_string()
-                    }
-                })
-                .collect::<Vec<_>>()
-                .join(", ");
-            format!("{}{}\n({})\n", docs, call_info.signature, params)
-        }
-        None => String::new(),
-    };
-    expect.assert_eq(&actual);
-}
-
-#[test]
-fn test_fn_signature_two_args() {
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo($03, ); }
-"#,
-        expect![[r#"
-                fn foo(x: u32, y: u32) -> u32
-                (<x: u32>, y: u32)
-            "#]],
-    );
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo(3$0, ); }
-"#,
-        expect![[r#"
-                fn foo(x: u32, y: u32) -> u32
-                (<x: u32>, y: u32)
-            "#]],
-    );
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo(3,$0 ); }
-"#,
-        expect![[r#"
-                fn foo(x: u32, y: u32) -> u32
-                (x: u32, <y: u32>)
-            "#]],
-    );
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo(3, $0); }
-"#,
-        expect![[r#"
-                fn foo(x: u32, y: u32) -> u32
-                (x: u32, <y: u32>)
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_two_args_empty() {
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo($0); }
-"#,
-        expect![[r#"
-                fn foo(x: u32, y: u32) -> u32
-                (<x: u32>, y: u32)
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_two_args_first_generics() {
-    check(
-        r#"
-fn foo<T, U: Copy + Display>(x: T, y: U) -> u32
-    where T: Copy + Display, U: Debug
-{ x + y }
-
-fn bar() { foo($03, ); }
-"#,
-        expect![[r#"
-                fn foo(x: i32, y: {unknown}) -> u32
-                (<x: i32>, y: {unknown})
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_no_params() {
-    check(
-        r#"
-fn foo<T>() -> T where T: Copy + Display {}
-fn bar() { foo($0); }
-"#,
-        expect![[r#"
-                fn foo() -> {unknown}
-                ()
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_for_impl() {
-    check(
-        r#"
-struct F;
-impl F { pub fn new() { } }
-fn bar() {
-    let _ : F = F::new($0);
-}
-"#,
-        expect![[r#"
-                fn new()
-                ()
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_for_method_self() {
-    check(
-        r#"
-struct S;
-impl S { pub fn do_it(&self) {} }
-
-fn bar() {
-    let s: S = S;
-    s.do_it($0);
-}
-"#,
-        expect![[r#"
-                fn do_it(&self)
-                ()
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_for_method_with_arg() {
-    check(
-        r#"
-struct S;
-impl S {
-    fn foo(&self, x: i32) {}
-}
-
-fn main() { S.foo($0); }
-"#,
-        expect![[r#"
-                fn foo(&self, x: i32)
-                (<x: i32>)
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_for_generic_method() {
-    check(
-        r#"
-struct S<T>(T);
-impl<T> S<T> {
-    fn foo(&self, x: T) {}
-}
-
-fn main() { S(1u32).foo($0); }
-"#,
-        expect![[r#"
-                fn foo(&self, x: u32)
-                (<x: u32>)
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_for_method_with_arg_as_assoc_fn() {
-    check(
-        r#"
-struct S;
-impl S {
-    fn foo(&self, x: i32) {}
-}
-
-fn main() { S::foo($0); }
-"#,
-        expect![[r#"
-                fn foo(self: &S, x: i32)
-                (<self: &S>, x: i32)
-            "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_with_docs_simple() {
-    check(
-        r#"
-/// test
-// non-doc-comment
-fn foo(j: u32) -> u32 {
-    j
-}
-
-fn bar() {
-    let _ = foo($0);
-}
-"#,
-        expect![[r#"
-            test
-            ------
-            fn foo(j: u32) -> u32
-            (<j: u32>)
-        "#]],
-    );
-}
-
-#[test]
-fn test_fn_signature_with_docs() {
-    check(
-        r#"
-/// Adds one to the number given.
-///
-/// # Examples
-///
-/// ```
-/// let five = 5;
-///
-/// assert_eq!(6, my_crate::add_one(5));
-/// ```
-pub fn add_one(x: i32) -> i32 {
-    x + 1
-}
-
-pub fn do() {
-    add_one($0
-}"#,
-        expect![[r##"
-            Adds one to the number given.
-
-            # Examples
-
-            ```
-            let five = 5;
-
-            assert_eq!(6, my_crate::add_one(5));
-            ```
-            ------
-            fn add_one(x: i32) -> i32
-            (<x: i32>)
-        "##]],
-    );
-}
-
-#[test]
-fn test_fn_signature_with_docs_impl() {
-    check(
-        r#"
-struct addr;
-impl addr {
-    /// Adds one to the number given.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let five = 5;
-    ///
-    /// assert_eq!(6, my_crate::add_one(5));
-    /// ```
-    pub fn add_one(x: i32) -> i32 {
-        x + 1
-    }
-}
-
-pub fn do_it() {
-    addr {};
-    addr::add_one($0);
-}
-"#,
-        expect![[r##"
-            Adds one to the number given.
-
-            # Examples
-
-            ```
-            let five = 5;
-
-            assert_eq!(6, my_crate::add_one(5));
-            ```
-            ------
-            fn add_one(x: i32) -> i32
-            (<x: i32>)
-        "##]],
-    );
-}
-
-#[test]
-fn test_fn_signature_with_docs_from_actix() {
-    check(
-        r#"
-struct WriteHandler<E>;
-
-impl<E> WriteHandler<E> {
-    /// Method is called when writer emits error.
-    ///
-    /// If this method returns `ErrorAction::Continue` writer processing
-    /// continues otherwise stream processing stops.
-    fn error(&mut self, err: E, ctx: &mut Self::Context) -> Running {
-        Running::Stop
-    }
-
-    /// Method is called when writer finishes.
-    ///
-    /// By default this method stops actor's `Context`.
-    fn finished(&mut self, ctx: &mut Self::Context) {
-        ctx.stop()
-    }
-}
-
-pub fn foo(mut r: WriteHandler<()>) {
-    r.finished($0);
-}
-"#,
-        expect![[r#"
-            Method is called when writer finishes.
-
-            By default this method stops actor's `Context`.
-            ------
-            fn finished(&mut self, ctx: &mut {unknown})
-            (<ctx: &mut {unknown}>)
-        "#]],
-    );
-}
-
-#[test]
-fn call_info_bad_offset() {
-    check(
-        r#"
-fn foo(x: u32, y: u32) -> u32 {x + y}
-fn bar() { foo $0 (3, ); }
-"#,
-        expect![[""]],
-    );
-}
-
-#[test]
-fn test_nested_method_in_lambda() {
-    check(
-        r#"
-struct Foo;
-impl Foo { fn bar(&self, _: u32) { } }
-
-fn bar(_: u32) { }
-
-fn main() {
-    let foo = Foo;
-    std::thread::spawn(move || foo.bar($0));
-}
-"#,
-        expect![[r#"
-                fn bar(&self, _: u32)
-                (<_: u32>)
-            "#]],
-    );
-}
-
-#[test]
-fn works_for_tuple_structs() {
-    check(
-        r#"
-/// A cool tuple struct
-struct S(u32, i32);
-fn main() {
-    let s = S(0, $0);
-}
-"#,
-        expect![[r#"
-            A cool tuple struct
-            ------
-            struct S(u32, i32)
-            (u32, <i32>)
-        "#]],
-    );
-}
-
-#[test]
-fn generic_struct() {
-    check(
-        r#"
-struct S<T>(T);
-fn main() {
-    let s = S($0);
-}
-"#,
-        expect![[r#"
-                struct S({unknown})
-                (<{unknown}>)
-            "#]],
-    );
-}
-
-#[test]
-fn works_for_enum_variants() {
-    check(
-        r#"
-enum E {
-    /// A Variant
-    A(i32),
-    /// Another
-    B,
-    /// And C
-    C { a: i32, b: i32 }
-}
-
-fn main() {
-    let a = E::A($0);
-}
-"#,
-        expect![[r#"
-            A Variant
-            ------
-            enum E::A(i32)
-            (<i32>)
-        "#]],
-    );
-}
-
-#[test]
-fn cant_call_struct_record() {
-    check(
-        r#"
-struct S { x: u32, y: i32 }
-fn main() {
-    let s = S($0);
-}
-"#,
-        expect![[""]],
-    );
-}
-
-#[test]
-fn cant_call_enum_record() {
-    check(
-        r#"
-enum E {
-    /// A Variant
-    A(i32),
-    /// Another
-    B,
-    /// And C
-    C { a: i32, b: i32 }
-}
-
-fn main() {
-    let a = E::C($0);
-}
-"#,
-        expect![[""]],
-    );
-}
-
-#[test]
-fn fn_signature_for_call_in_macro() {
-    check(
-        r#"
-macro_rules! id { ($($tt:tt)*) => { $($tt)* } }
-fn foo() { }
-id! {
-    fn bar() { foo($0); }
-}
-"#,
-        expect![[r#"
-                fn foo()
-                ()
-            "#]],
-    );
-}
-
-#[test]
-fn call_info_for_lambdas() {
-    check(
-        r#"
-struct S;
-fn foo(s: S) -> i32 { 92 }
-fn main() {
-    (|s| foo(s))($0)
-}
-        "#,
-        expect![[r#"
-                (S) -> i32
-                (<S>)
-            "#]],
-    )
-}
-
-#[test]
-fn call_info_for_fn_ptr() {
-    check(
-        r#"
-fn main(f: fn(i32, f64) -> char) {
-    f(0, $0)
-}
-        "#,
-        expect![[r#"
-                (i32, f64) -> char
-                (i32, <f64>)
-            "#]],
-    )
-}
-
-#[test]
-fn call_info_for_unclosed_call() {
-    check(
-        r#"
-fn foo(foo: u32, bar: u32) {}
-fn main() {
-    foo($0
-}"#,
-        expect![[r#"
-            fn foo(foo: u32, bar: u32)
-            (<foo: u32>, bar: u32)
-        "#]],
-    );
-    // check with surrounding space
-    check(
-        r#"
-fn foo(foo: u32, bar: u32) {}
-fn main() {
-    foo( $0
-}"#,
-        expect![[r#"
-            fn foo(foo: u32, bar: u32)
-            (<foo: u32>, bar: u32)
-        "#]],
-    )
-}
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 77db09315d9..1250008984e 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -13,12 +13,12 @@ pub mod items_locator;
 pub mod source_change;
 pub mod ty_filter;
 pub mod traits;
-pub mod call_info;
 pub mod helpers;
 pub mod path_transform;
 
 pub mod search;
 pub mod rename;
+pub mod active_parameter;
 
 use std::{fmt, mem::ManuallyDrop, sync::Arc};