4 files changed, 396 insertions, 56 deletions

diff --git a/crates/assists/src/handlers/qualify_path.rs b/crates/assists/src/handlers/qualify_path.rs
index f436bdbbf..d5bc4e574 100644
--- a/crates/assists/src/handlers/qualify_path.rs
+++ b/crates/assists/src/handlers/qualify_path.rs
@@ -56,12 +56,14 @@ pub(crate) fn qualify_path(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
         ImportCandidate::QualifierStart(_) => {
             mark::hit!(qualify_path_qualifier_start);
             let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
-            let segment = path.segment()?;
-            QualifyCandidate::QualifierStart(segment)
+            let (prev_segment, segment) = (path.qualifier()?.segment()?, path.segment()?);
+            QualifyCandidate::QualifierStart(segment, prev_segment.generic_arg_list())
         }
         ImportCandidate::UnqualifiedName(_) => {
             mark::hit!(qualify_path_unqualified_name);
-            QualifyCandidate::UnqualifiedName
+            let path = ast::Path::cast(import_assets.syntax_under_caret().clone())?;
+            let generics = path.segment()?.generic_arg_list();
+            QualifyCandidate::UnqualifiedName(generics)
         }
         ImportCandidate::TraitAssocItem(_) => {
             mark::hit!(qualify_path_trait_assoc_item);
@@ -96,22 +98,25 @@ pub(crate) fn qualify_path(acc: &mut Assists, ctx: &AssistContext) -> Option<()>
 }
 
 enum QualifyCandidate<'db> {
-    QualifierStart(ast::PathSegment),
-    UnqualifiedName,
+    QualifierStart(ast::PathSegment, Option<ast::GenericArgList>),
+    UnqualifiedName(Option<ast::GenericArgList>),
     TraitAssocItem(ast::Path, ast::PathSegment),
     TraitMethod(&'db RootDatabase, ast::MethodCallExpr),
 }
 
 impl QualifyCandidate<'_> {
     fn qualify(&self, mut replacer: impl FnMut(String), import: hir::ModPath, item: hir::ItemInNs) {
+        let import = mod_path_to_ast(&import);
         match self {
-            QualifyCandidate::QualifierStart(segment) => {
-                let import = mod_path_to_ast(&import);
-                replacer(format!("{}::{}", import, segment));
+            QualifyCandidate::QualifierStart(segment, generics) => {
+                let generics = generics.as_ref().map_or_else(String::new, ToString::to_string);
+                replacer(format!("{}{}::{}", import, generics, segment));
+            }
+            QualifyCandidate::UnqualifiedName(generics) => {
+                let generics = generics.as_ref().map_or_else(String::new, ToString::to_string);
+                replacer(format!("{}{}", import.to_string(), generics));
             }
-            QualifyCandidate::UnqualifiedName => replacer(mod_path_to_ast(&import).to_string()),
             QualifyCandidate::TraitAssocItem(qualifier, segment) => {
-                let import = mod_path_to_ast(&import);
                 replacer(format!("<{} as {}>::{}", qualifier, import, segment));
             }
             &QualifyCandidate::TraitMethod(db, ref mcall_expr) => {
@@ -124,25 +129,27 @@ impl QualifyCandidate<'_> {
         db: &RootDatabase,
         mcall_expr: &ast::MethodCallExpr,
         mut replacer: impl FnMut(String),
-        import: hir::ModPath,
+        import: ast::Path,
         item: hir::ItemInNs,
     ) -> Option<()> {
         let receiver = mcall_expr.receiver()?;
         let trait_method_name = mcall_expr.name_ref()?;
+        let generics =
+            mcall_expr.generic_arg_list().as_ref().map_or_else(String::new, ToString::to_string);
         let arg_list = mcall_expr.arg_list().map(|arg_list| arg_list.args());
         let trait_ = item_as_trait(item)?;
         let method = find_trait_method(db, trait_, &trait_method_name)?;
         if let Some(self_access) = method.self_param(db).map(|sp| sp.access(db)) {
-            let import = mod_path_to_ast(&import);
             let receiver = match self_access {
                 hir::Access::Shared => make::expr_ref(receiver, false),
                 hir::Access::Exclusive => make::expr_ref(receiver, true),
                 hir::Access::Owned => receiver,
             };
             replacer(format!(
-                "{}::{}{}",
+                "{}::{}{}{}",
                 import,
                 trait_method_name,
+                generics,
                 match arg_list.clone() {
                     Some(args) => make::arg_list(iter::once(receiver).chain(args)),
                     None => make::arg_list(iter::once(receiver)),
@@ -1045,4 +1052,153 @@ fn main() {
 ",
         );
     }
+
+    #[test]
+    fn keep_generic_annotations() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub mod generic { pub struct Thing<'a, T>(&'a T); }
+
+//- /main.rs crate:main deps:dep
+fn foo() -> Thin<|>g<'static, ()> {}
+
+fn main() {}
+",
+            r"
+fn foo() -> dep::generic::Thing<'static, ()> {}
+
+fn main() {}
+",
+        );
+    }
+
+    #[test]
+    fn keep_generic_annotations_leading_colon() {
+        check_assist(
+            qualify_path,
+            r"
+//- /lib.rs crate:dep
+pub mod generic { pub struct Thing<'a, T>(&'a T); }
+
+//- /main.rs crate:main deps:dep
+fn foo() -> Thin<|>g::<'static, ()> {}
+
+fn main() {}
+",
+            r"
+fn foo() -> dep::generic::Thing::<'static, ()> {}
+
+fn main() {}
+",
+        );
+    }
+
+    #[test]
+    fn associated_struct_const_generic() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub struct TestStruct<T> {}
+                impl<T> TestStruct<T> {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                TestStruct::<()>::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub struct TestStruct<T> {}
+                impl<T> TestStruct<T> {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::<()>::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn associated_trait_const_generic() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct<T> {}
+                impl<T> TestTrait for TestStruct<T> {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                test_mod::TestStruct::<()>::TEST_CONST<|>
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    const TEST_CONST: u8;
+                }
+                pub struct TestStruct<T> {}
+                impl<T> TestTrait for TestStruct<T> {
+                    const TEST_CONST: u8 = 42;
+                }
+            }
+
+            fn main() {
+                <test_mod::TestStruct::<()> as test_mod::TestTrait>::TEST_CONST
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn trait_method_generic() {
+        check_assist(
+            qualify_path,
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method<T>(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method<T>(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_struct.test_meth<|>od::<()>()
+            }
+            ",
+            r"
+            mod test_mod {
+                pub trait TestTrait {
+                    fn test_method<T>(&self);
+                }
+                pub struct TestStruct {}
+                impl TestTrait for TestStruct {
+                    fn test_method<T>(&self) {}
+                }
+            }
+
+            fn main() {
+                let test_struct = test_mod::TestStruct {};
+                test_mod::TestTrait::test_method::<()>(&test_struct)
+            }
+            ",
+        );
+    }
 }
diff --git a/crates/ide/src/diagnostics.rs b/crates/ide/src/diagnostics.rs
index d0ee58858..1c7f02763 100644
--- a/crates/ide/src/diagnostics.rs
+++ b/crates/ide/src/diagnostics.rs
@@ -613,7 +613,7 @@ fn main() {
 pub struct Foo { pub a: i32, pub b: i32 }
 "#,
             r#"
-fn some(, b: ()} {}
+fn some(, b: ()) {}
 fn items() {}
 fn here() {}
 
diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
index adb93efd7..ac704ae21 100644
--- a/crates/ide/src/inlay_hints.rs
+++ b/crates/ide/src/inlay_hints.rs
@@ -1,6 +1,6 @@
 use assists::utils::FamousDefs;
 use either::Either;
-use hir::{known, HirDisplay, Semantics};
+use hir::{known, Callable, HirDisplay, Semantics};
 use ide_db::RootDatabase;
 use stdx::to_lower_snake_case;
 use syntax::{
@@ -170,7 +170,7 @@ fn get_param_name_hints(
             };
             Some((param_name, arg))
         })
-        .filter(|(param_name, arg)| should_show_param_name_hint(sema, &callable, &param_name, &arg))
+        .filter(|(param_name, arg)| should_show_param_name_hint(sema, &callable, param_name, &arg))
         .map(|(param_name, arg)| InlayHint {
             range: arg.syntax().text_range(),
             kind: InlayKind::ParameterHint,
@@ -334,9 +334,11 @@ fn should_show_param_name_hint(
         | hir::CallableKind::TupleEnumVariant(_)
         | hir::CallableKind::Closure => None,
     };
+
     if param_name.is_empty()
         || Some(param_name) == fn_name.as_ref().map(|s| s.trim_start_matches('_'))
         || is_argument_similar_to_param_name(sema, argument, param_name)
+        || is_param_name_similar_to_fn_name(param_name, callable, fn_name.as_ref())
         || param_name.starts_with("ra_fixture")
     {
         return false;
@@ -364,6 +366,26 @@ fn is_argument_similar_to_param_name(
     }
 }
 
+fn is_param_name_similar_to_fn_name(
+    param_name: &str,
+    callable: &Callable,
+    fn_name: Option<&String>,
+) -> bool {
+    // if it's the only parameter, don't show it if:
+    // - is the same as the function name, or
+    // - the function ends with '_' + param_name
+
+    match (callable.n_params(), fn_name) {
+        (1, Some(function)) => {
+            function == param_name
+                || (function.len() > param_name.len()
+                    && function.ends_with(param_name)
+                    && function[..function.len() - param_name.len()].ends_with('_'))
+        }
+        _ => false,
+    }
+}
+
 fn is_enum_name_similar_to_param_name(
     sema: &Semantics<RootDatabase>,
     argument: &ast::Expr,
@@ -457,6 +479,88 @@ fn main() {
     }
 
     #[test]
+    fn param_name_similar_to_fn_name_still_hints() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: true,
+                type_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn max(x: i32, y: i32) -> i32 { x + y }
+fn main() {
+    let _x = max(
+        4,
+      //^ x
+        4,
+      //^ y
+    );
+}"#,
+        );
+    }
+
+    #[test]
+    fn param_name_similar_to_fn_name() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: true,
+                type_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn param_with_underscore(with_underscore: i32) -> i32 { with_underscore }
+fn main() {
+    let _x = param_with_underscore(
+        4,
+    );
+}"#,
+        );
+    }
+
+    #[test]
+    fn param_name_same_as_fn_name() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: true,
+                type_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn foo(foo: i32) -> i32 { foo }
+fn main() {
+    let _x = foo(
+        4,
+    );
+}"#,
+        );
+    }
+
+    #[test]
+    fn never_hide_param_when_multiple_params() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: true,
+                type_hints: false,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+fn foo(bar: i32, baz: i32) -> i32 { bar + baz }
+fn main() {
+    let _x = foo(
+        4,
+      //^ bar
+        8,
+      //^ baz
+    );
+}"#,
+        );
+    }
+
+    #[test]
     fn hints_disabled() {
         check_with_config(
             InlayHintsConfig {
diff --git a/crates/syntax/src/algo.rs b/crates/syntax/src/algo.rs
index 065035fe6..9dc7182bd 100644
--- a/crates/syntax/src/algo.rs
+++ b/crates/syntax/src/algo.rs
@@ -137,7 +137,7 @@ impl TreeDiff {
     }
 }
 
-/// Finds minimal the diff, which, applied to `from`, will result in `to`.
+/// Finds a (potentially minimal) diff, which, applied to `from`, will result in `to`.
 ///
 /// Specifically, returns a structure that consists of a replacements, insertions and deletions
 /// such that applying this map on `from` will result in `to`.
@@ -151,7 +151,6 @@ pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
     };
     let (from, to) = (from.clone().into(), to.clone().into());
 
-    // FIXME: this is horrible inefficient. I bet there's a cool algorithm to diff trees properly.
     if !syntax_element_eq(&from, &to) {
         go(&mut diff, from, to);
     }
@@ -169,6 +168,7 @@ pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
             }
     }
 
+    // FIXME: this is horrible inefficient. I bet there's a cool algorithm to diff trees properly.
     fn go(diff: &mut TreeDiff, lhs: SyntaxElement, rhs: SyntaxElement) {
         let (lhs, rhs) = match lhs.as_node().zip(rhs.as_node()) {
             Some((lhs, rhs)) => (lhs, rhs),
@@ -179,6 +179,8 @@ pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
             }
         };
 
+        let mut look_ahead_scratch = Vec::default();
+
         let mut rhs_children = rhs.children_with_tokens();
         let mut lhs_children = lhs.children_with_tokens();
         let mut last_lhs = None;
@@ -204,7 +206,31 @@ pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
                     diff.deletions.push(element);
                 }
                 (Some(ref lhs_ele), Some(ref rhs_ele)) if syntax_element_eq(lhs_ele, rhs_ele) => {}
-                (Some(lhs_ele), Some(rhs_ele)) => go(diff, lhs_ele, rhs_ele),
+                (Some(lhs_ele), Some(rhs_ele)) => {
+                    // nodes differ, look for lhs_ele in rhs, if its found we can mark everything up
+                    // until that element as insertions. This is important to keep the diff minimal
+                    // in regards to insertions that have been actually done, this is important for
+                    // use insertions as we do not want to replace the entire module node.
+                    look_ahead_scratch.push(rhs_ele.clone());
+                    let mut rhs_children_clone = rhs_children.clone();
+                    let mut insert = false;
+                    while let Some(rhs_child) = rhs_children_clone.next() {
+                        if syntax_element_eq(&lhs_ele, &rhs_child) {
+                            mark::hit!(diff_insertions);
+                            insert = true;
+                            break;
+                        } else {
+                            look_ahead_scratch.push(rhs_child);
+                        }
+                    }
+                    let drain = look_ahead_scratch.drain(..);
+                    if let Some(prev) = last_lhs.clone().filter(|_| insert) {
+                        diff.insertions.entry(prev).or_insert_with(Vec::new).extend(drain);
+                        rhs_children = rhs_children_clone;
+                    } else {
+                        go(diff, lhs_ele, rhs_ele)
+                    }
+                }
             }
             last_lhs = lhs_child.or(last_lhs);
         }
@@ -292,7 +318,6 @@ fn _replace_children(
 #[derive(Debug, PartialEq, Eq, Hash)]
 enum InsertPos {
     FirstChildOf(SyntaxNode),
-    // Before(SyntaxElement),
     After(SyntaxElement),
 }
 
@@ -603,18 +628,44 @@ mod tests {
     }
 
     #[test]
-    fn insert() {
+    fn replace_parent() {
+        mark::check!(diff_replace_parent);
+        check_diff(
+            r#""#,
+            r#"use foo::bar;"#,
+            expect![[r#"
+                insertions:
+
+
+
+                replacements:
+
+                Line 0: Node([email protected]) -> use foo::bar;
+
+                deletions:
+
+
+            "#]],
+        );
+    }
+
+    #[test]
+    fn insert_last() {
         mark::check!(diff_insert);
         check_diff(
-            r#"use foo;"#,
-            r#"use foo;
+            r#"
+use foo;
 use bar;"#,
+            r#"
+use foo;
+use bar;
+use baz;"#,
             expect![[r#"
                 insertions:
 
-                Line 0: Node([email protected])
+                Line 2: Node(USE@10..18)
                 -> "\n"
-                -> use bar;
+                -> use baz;
 
                 replacements:
 
@@ -628,29 +679,63 @@ use bar;"#,
     }
 
     #[test]
-    fn replace_parent() {
-        mark::check!(diff_replace_parent);
+    fn insert_middle() {
         check_diff(
-            r#""#,
-            r#"use foo::bar;"#,
+            r#"
+use foo;
+use baz;"#,
+            r#"
+use foo;
+use bar;
+use baz;"#,
             expect![[r#"
                 insertions:
 
+                Line 2: Token([email protected] "\n")
+                -> use bar;
+                -> "\n"
+
+                replacements:
+
+
+
+                deletions:
+
+
+            "#]],
+        )
+    }
+
+    #[test]
+    fn insert_first() {
+        check_diff(
+            r#"
+use bar;
+use baz;"#,
+            r#"
+use foo;
+use bar;
+use baz;"#,
+            expect![[r#"
+                insertions:
 
+                Line 0: Token([email protected] "\n")
+                -> use foo;
+                -> "\n"
 
                 replacements:
 
-                Line 0: Node([email protected]) -> use foo::bar;
+
 
                 deletions:
 
 
             "#]],
-        );
+        )
     }
 
     #[test]
-    fn delete() {
+    fn delete_last() {
         mark::check!(diff_delete);
         check_diff(
             r#"use foo;
@@ -674,52 +759,50 @@ use bar;"#,
     }
 
     #[test]
-    fn insert_use() {
+    fn delete_middle() {
+        mark::check!(diff_insertions);
         check_diff(
             r#"
 use expect_test::{expect, Expect};
+use text_edit::TextEdit;
 
 use crate::AstNode;
 "#,
             r#"
 use expect_test::{expect, Expect};
-use text_edit::TextEdit;
 
 use crate::AstNode;
 "#,
             expect![[r#"
                 insertions:
 
-                Line 4: Token([email protected] "\n")
+                Line 1: Node([email protected])
+                -> "\n\n"
                 -> use crate::AstNode;
-                -> "\n"
 
                 replacements:
 
-                Line 2: Token([email protected] "\n\n") -> "\n"
-                Line 4: Token([email protected] "crate") -> text_edit
-                Line 4: Token([email protected] "AstNode") -> TextEdit
-                Line 4: Token([email protected] "\n") -> "\n\n"
 
-                deletions:
 
+                deletions:
 
+                Line 2: use text_edit::TextEdit;
+                Line 3: "\n\n"
+                Line 4: use crate::AstNode;
+                Line 5: "\n"
             "#]],
         )
     }
 
     #[test]
-    fn remove_use() {
+    fn delete_first() {
         check_diff(
             r#"
-use expect_test::{expect, Expect};
 use text_edit::TextEdit;
 
 use crate::AstNode;
 "#,
             r#"
-use expect_test::{expect, Expect};
-
 use crate::AstNode;
 "#,
             expect![[r#"
@@ -729,15 +812,14 @@ use crate::AstNode;
 
                 replacements:
 
-                Line 2: Token([email protected] "\n") -> "\n\n"
-                Line 3: Node([email protected]) -> crate
-                Line 3: Token([email protected] "TextEdit") -> AstNode
-                Line 3: Token([email protected] "\n\n") -> "\n"
+                Line 2: Node([email protected]) -> crate
+                Line 2: Token([email protected] "TextEdit") -> AstNode
+                Line 2: Token([email protected] "\n\n") -> "\n"
 
                 deletions:
 
-                Line 4: use crate::AstNode;
-                Line 5: "\n"
+                Line 3: use crate::AstNode;
+                Line 4: "\n"
             "#]],
         )
     }
@@ -814,17 +896,15 @@ fn main() {
                         _ => return,
                     }
                 -> ;
-                Line 5: Token(R_CURLY@64..65 "}")
-                -> "\n"
-                -> }
+                Line 3: Node(IF_EXPR@17..63)
+                -> "\n    "
+                -> foo(x);
 
                 replacements:
 
                 Line 3: Token([email protected] "if") -> let
                 Line 3: Token([email protected] "let") -> x
                 Line 3: Node([email protected]) -> =
-                Line 5: Token([email protected] "\n") -> "\n    "
-                Line 5: Token([email protected] "}") -> foo(x);
 
                 deletions: