1 files changed, 398 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/replace_derive_with_manual_impl.rs b/crates/assists/src/handlers/replace_derive_with_manual_impl.rs
new file mode 100644
index 000000000..82625516c
--- /dev/null
+++ b/crates/assists/src/handlers/replace_derive_with_manual_impl.rs
@@ -0,0 +1,398 @@
+use ide_db::imports_locator;
+use itertools::Itertools;
+use syntax::{
+    ast::{self, make, AstNode},
+    Direction, SmolStr,
+    SyntaxKind::{IDENT, WHITESPACE},
+    TextSize,
+};
+
+use crate::{
+    assist_context::{AssistBuilder, AssistContext, Assists},
+    utils::{
+        add_trait_assoc_items_to_impl, filter_assoc_items, mod_path_to_ast, render_snippet, Cursor,
+        DefaultMethods,
+    },
+    AssistId, AssistKind,
+};
+
+// Assist: replace_derive_with_manual_impl
+//
+// Converts a `derive` impl into a manual one.
+//
+// ```
+// # trait Debug { fn fmt(&self, f: &mut Formatter) -> Result<()>; }
+// #[derive(Deb<|>ug, Display)]
+// struct S;
+// ```
+// ->
+// ```
+// # trait Debug { fn fmt(&self, f: &mut Formatter) -> Result<()>; }
+// #[derive(Display)]
+// struct S;
+//
+// impl Debug for S {
+//     fn fmt(&self, f: &mut Formatter) -> Result<()> {
+//         ${0:todo!()}
+//     }
+// }
+// ```
+pub(crate) fn replace_derive_with_manual_impl(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+) -> Option<()> {
+    let attr = ctx.find_node_at_offset::<ast::Attr>()?;
+
+    let attr_name = attr
+        .syntax()
+        .descendants_with_tokens()
+        .filter(|t| t.kind() == IDENT)
+        .find_map(syntax::NodeOrToken::into_token)
+        .filter(|t| t.text() == "derive")?
+        .text()
+        .clone();
+
+    let trait_token =
+        ctx.token_at_offset().find(|t| t.kind() == IDENT && *t.text() != attr_name)?;
+    let trait_path = make::path_unqualified(make::path_segment(make::name_ref(trait_token.text())));
+
+    let annotated_name = attr.syntax().siblings(Direction::Next).find_map(ast::Name::cast)?;
+    let insert_pos = annotated_name.syntax().parent()?.text_range().end();
+
+    let current_module = ctx.sema.scope(annotated_name.syntax()).module()?;
+    let current_crate = current_module.krate();
+
+    let found_traits = imports_locator::find_imports(&ctx.sema, current_crate, trait_token.text())
+        .into_iter()
+        .filter_map(|candidate: either::Either<hir::ModuleDef, hir::MacroDef>| match candidate {
+            either::Either::Left(hir::ModuleDef::Trait(trait_)) => Some(trait_),
+            _ => None,
+        })
+        .flat_map(|trait_| {
+            current_module
+                .find_use_path(ctx.sema.db, hir::ModuleDef::Trait(trait_))
+                .as_ref()
+                .map(mod_path_to_ast)
+                .zip(Some(trait_))
+        });
+
+    let mut no_traits_found = true;
+    for (trait_path, trait_) in found_traits.inspect(|_| no_traits_found = false) {
+        add_assist(acc, ctx, &attr, &trait_path, Some(trait_), &annotated_name, insert_pos)?;
+    }
+    if no_traits_found {
+        add_assist(acc, ctx, &attr, &trait_path, None, &annotated_name, insert_pos)?;
+    }
+    Some(())
+}
+
+fn add_assist(
+    acc: &mut Assists,
+    ctx: &AssistContext,
+    attr: &ast::Attr,
+    trait_path: &ast::Path,
+    trait_: Option<hir::Trait>,
+    annotated_name: &ast::Name,
+    insert_pos: TextSize,
+) -> Option<()> {
+    let target = attr.syntax().text_range();
+    let input = attr.token_tree()?;
+    let label = format!("Convert to manual  `impl {} for {}`", trait_path, annotated_name);
+    let trait_name = trait_path.segment().and_then(|seg| seg.name_ref())?;
+
+    acc.add(
+        AssistId("replace_derive_with_manual_impl", AssistKind::Refactor),
+        label,
+        target,
+        |builder| {
+            let impl_def_with_items =
+                impl_def_from_trait(&ctx.sema, annotated_name, trait_, trait_path);
+            update_attribute(builder, &input, &trait_name, &attr);
+            match (ctx.config.snippet_cap, impl_def_with_items) {
+                (None, _) => builder.insert(
+                    insert_pos,
+                    format!("\n\nimpl {} for {} {{\n\n}}", trait_path, annotated_name),
+                ),
+                (Some(cap), None) => builder.insert_snippet(
+                    cap,
+                    insert_pos,
+                    format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_path, annotated_name),
+                ),
+                (Some(cap), Some((impl_def, first_assoc_item))) => {
+                    let mut cursor = Cursor::Before(first_assoc_item.syntax());
+                    let placeholder;
+                    if let ast::AssocItem::Fn(ref func) = first_assoc_item {
+                        if let Some(m) = func.syntax().descendants().find_map(ast::MacroCall::cast)
+                        {
+                            if m.syntax().text() == "todo!()" {
+                                placeholder = m;
+                                cursor = Cursor::Replace(placeholder.syntax());
+                            }
+                        }
+                    }
+
+                    builder.insert_snippet(
+                        cap,
+                        insert_pos,
+                        format!("\n\n{}", render_snippet(cap, impl_def.syntax(), cursor)),
+                    )
+                }
+            };
+        },
+    )
+}
+
+fn impl_def_from_trait(
+    sema: &hir::Semantics<ide_db::RootDatabase>,
+    annotated_name: &ast::Name,
+    trait_: Option<hir::Trait>,
+    trait_path: &ast::Path,
+) -> Option<(ast::Impl, ast::AssocItem)> {
+    let trait_ = trait_?;
+    let target_scope = sema.scope(annotated_name.syntax());
+    let trait_items = filter_assoc_items(sema.db, &trait_.items(sema.db), DefaultMethods::No);
+    if trait_items.is_empty() {
+        return None;
+    }
+    let impl_def = make::impl_trait(
+        trait_path.clone(),
+        make::path_unqualified(make::path_segment(make::name_ref(annotated_name.text()))),
+    );
+    let (impl_def, first_assoc_item) =
+        add_trait_assoc_items_to_impl(sema, trait_items, trait_, impl_def, target_scope);
+    Some((impl_def, first_assoc_item))
+}
+
+fn update_attribute(
+    builder: &mut AssistBuilder,
+    input: &ast::TokenTree,
+    trait_name: &ast::NameRef,
+    attr: &ast::Attr,
+) {
+    let new_attr_input = input
+        .syntax()
+        .descendants_with_tokens()
+        .filter(|t| t.kind() == IDENT)
+        .filter_map(|t| t.into_token().map(|t| t.text().clone()))
+        .filter(|t| t != trait_name.text())
+        .collect::<Vec<SmolStr>>();
+    let has_more_derives = !new_attr_input.is_empty();
+
+    if has_more_derives {
+        let new_attr_input = format!("({})", new_attr_input.iter().format(", "));
+        builder.replace(input.syntax().text_range(), new_attr_input);
+    } else {
+        let attr_range = attr.syntax().text_range();
+        builder.delete(attr_range);
+
+        if let Some(line_break_range) = attr
+            .syntax()
+            .next_sibling_or_token()
+            .filter(|t| t.kind() == WHITESPACE)
+            .map(|t| t.text_range())
+        {
+            builder.delete(line_break_range);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn add_custom_impl_debug() {
+        check_assist(
+            replace_derive_with_manual_impl,
+            "
+mod fmt {
+    pub struct Error;
+    pub type Result = Result<(), Error>;
+    pub struct Formatter<'a>;
+    pub trait Debug {
+        fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+    }
+}
+
+#[derive(Debu<|>g)]
+struct Foo {
+    bar: String,
+}
+",
+            "
+mod fmt {
+    pub struct Error;
+    pub type Result = Result<(), Error>;
+    pub struct Formatter<'a>;
+    pub trait Debug {
+        fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+    }
+}
+
+struct Foo {
+    bar: String,
+}
+
+impl fmt::Debug for Foo {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        ${0:todo!()}
+    }
+}
+",
+        )
+    }
+    #[test]
+    fn add_custom_impl_all() {
+        check_assist(
+            replace_derive_with_manual_impl,
+            "
+mod foo {
+    pub trait Bar {
+        type Qux;
+        const Baz: usize = 42;
+        const Fez: usize;
+        fn foo();
+        fn bar() {}
+    }
+}
+
+#[derive(<|>Bar)]
+struct Foo {
+    bar: String,
+}
+",
+            "
+mod foo {
+    pub trait Bar {
+        type Qux;
+        const Baz: usize = 42;
+        const Fez: usize;
+        fn foo();
+        fn bar() {}
+    }
+}
+
+struct Foo {
+    bar: String,
+}
+
+impl foo::Bar for Foo {
+    $0type Qux;
+
+    const Baz: usize = 42;
+
+    const Fez: usize;
+
+    fn foo() {
+        todo!()
+    }
+}
+",
+        )
+    }
+    #[test]
+    fn add_custom_impl_for_unique_input() {
+        check_assist(
+            replace_derive_with_manual_impl,
+            "
+#[derive(Debu<|>g)]
+struct Foo {
+    bar: String,
+}
+            ",
+            "
+struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_for_with_visibility_modifier() {
+        check_assist(
+            replace_derive_with_manual_impl,
+            "
+#[derive(Debug<|>)]
+pub struct Foo {
+    bar: String,
+}
+            ",
+            "
+pub struct Foo {
+    bar: String,
+}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn add_custom_impl_when_multiple_inputs() {
+        check_assist(
+            replace_derive_with_manual_impl,
+            "
+#[derive(Display, Debug<|>, Serialize)]
+struct Foo {}
+            ",
+            "
+#[derive(Display, Serialize)]
+struct Foo {}
+
+impl Debug for Foo {
+    $0
+}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_derive_macro_without_input() {
+        check_assist_not_applicable(
+            replace_derive_with_manual_impl,
+            "
+#[derive(<|>)]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_cursor_on_param() {
+        check_assist_not_applicable(
+            replace_derive_with_manual_impl,
+            "
+#[derive<|>(Debug)]
+struct Foo {}
+            ",
+        );
+
+        check_assist_not_applicable(
+            replace_derive_with_manual_impl,
+            "
+#[derive(Debug)<|>]
+struct Foo {}
+            ",
+        )
+    }
+
+    #[test]
+    fn test_ignore_if_not_derive() {
+        check_assist_not_applicable(
+            replace_derive_with_manual_impl,
+            "
+#[allow(non_camel_<|>case_types)]
+struct Foo {}
+            ",
+        )
+    }
+}