1 files changed, 424 insertions, 0 deletions

diff --git a/crates/ra_assists/src/handlers/generate_new.rs b/crates/ra_assists/src/handlers/generate_new.rs
new file mode 100644
index 000000000..e27def1d8
--- /dev/null
+++ b/crates/ra_assists/src/handlers/generate_new.rs
@@ -0,0 +1,424 @@
+use hir::Adt;
+use ra_syntax::{
+    ast::{
+        self, AstNode, NameOwner, StructKind, TypeAscriptionOwner, TypeParamsOwner, VisibilityOwner,
+    },
+    T,
+};
+use stdx::{format_to, SepBy};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_new
+//
+// Adds a new inherent impl for a type.
+//
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//     fn $0new(data: T) -> Self { Self { data } }
+// }
+//
+// ```
+pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let strukt = ctx.find_node_at_offset::<ast::StructDef>()?;
+
+    // We want to only apply this to non-union structs with named fields
+    let field_list = match strukt.kind() {
+        StructKind::Record(named) => named,
+        _ => return None,
+    };
+
+    // Return early if we've found an existing new fn
+    let impl_def = find_struct_impl(&ctx, &strukt)?;
+
+    let target = strukt.syntax().text_range();
+    acc.add(AssistId("generate_new", AssistKind::Generate), "Generate `new`", target, |builder| {
+        let mut buf = String::with_capacity(512);
+
+        if impl_def.is_some() {
+            buf.push('\n');
+        }
+
+        let vis = strukt.visibility().map_or(String::new(), |v| format!("{} ", v));
+
+        let params = field_list
+            .fields()
+            .filter_map(|f| {
+                Some(format!("{}: {}", f.name()?.syntax(), f.ascribed_type()?.syntax()))
+            })
+            .sep_by(", ");
+        let fields = field_list.fields().filter_map(|f| f.name()).sep_by(", ");
+
+        format_to!(buf, "    {}fn new({}) -> Self {{ Self {{ {} }} }}", vis, params, fields);
+
+        let start_offset = impl_def
+            .and_then(|impl_def| {
+                buf.push('\n');
+                let start = impl_def
+                    .syntax()
+                    .descendants_with_tokens()
+                    .find(|t| t.kind() == T!['{'])?
+                    .text_range()
+                    .end();
+
+                Some(start)
+            })
+            .unwrap_or_else(|| {
+                buf = generate_impl_text(&strukt, &buf);
+                strukt.syntax().text_range().end()
+            });
+
+        match ctx.config.snippet_cap {
+            None => builder.insert(start_offset, buf),
+            Some(cap) => {
+                buf = buf.replace("fn new", "fn $0new");
+                builder.insert_snippet(cap, start_offset, buf);
+            }
+        }
+    })
+}
+
+// Generates the surrounding `impl Type { <code> }` including type and lifetime
+// parameters
+fn generate_impl_text(strukt: &ast::StructDef, code: &str) -> String {
+    let type_params = strukt.type_param_list();
+    let mut buf = String::with_capacity(code.len());
+    buf.push_str("\n\nimpl");
+    if let Some(type_params) = &type_params {
+        format_to!(buf, "{}", type_params.syntax());
+    }
+    buf.push_str(" ");
+    buf.push_str(strukt.name().unwrap().text().as_str());
+    if let Some(type_params) = type_params {
+        let lifetime_params = type_params
+            .lifetime_params()
+            .filter_map(|it| it.lifetime_token())
+            .map(|it| it.text().clone());
+        let type_params =
+            type_params.type_params().filter_map(|it| it.name()).map(|it| it.text().clone());
+        format_to!(buf, "<{}>", lifetime_params.chain(type_params).sep_by(", "))
+    }
+
+    format_to!(buf, " {{\n{}\n}}\n", code);
+
+    buf
+}
+
+// Uses a syntax-driven approach to find any impl blocks for the struct that
+// exist within the module/file
+//
+// Returns `None` if we've found an existing `new` fn
+//
+// FIXME: change the new fn checking to a more semantic approach when that's more
+// viable (e.g. we process proc macros, etc)
+fn find_struct_impl(ctx: &AssistContext, strukt: &ast::StructDef) -> Option<Option<ast::ImplDef>> {
+    let db = ctx.db();
+    let module = strukt.syntax().ancestors().find(|node| {
+        ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
+    })?;
+
+    let struct_def = ctx.sema.to_def(strukt)?;
+
+    let block = module.descendants().filter_map(ast::ImplDef::cast).find_map(|impl_blk| {
+        let blk = ctx.sema.to_def(&impl_blk)?;
+
+        // FIXME: handle e.g. `struct S<T>; impl<U> S<U> {}`
+        // (we currently use the wrong type parameter)
+        // also we wouldn't want to use e.g. `impl S<u32>`
+        let same_ty = match blk.target_ty(db).as_adt() {
+            Some(def) => def == Adt::Struct(struct_def),
+            None => false,
+        };
+        let not_trait_impl = blk.target_trait(db).is_none();
+
+        if !(same_ty && not_trait_impl) {
+            None
+        } else {
+            Some(impl_blk)
+        }
+    });
+
+    if let Some(ref impl_blk) = block {
+        if has_new_fn(impl_blk) {
+            return None;
+        }
+    }
+
+    Some(block)
+}
+
+fn has_new_fn(imp: &ast::ImplDef) -> bool {
+    if let Some(il) = imp.item_list() {
+        for item in il.assoc_items() {
+            if let ast::AssocItem::FnDef(f) = item {
+                if let Some(name) = f.name() {
+                    if name.text().eq_ignore_ascii_case("new") {
+                        return true;
+                    }
+                }
+            }
+        }
+    }
+
+    false
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    #[rustfmt::skip]
+    fn test_generate_new() {
+        // Check output of generation
+        check_assist(
+            generate_new,
+"struct Foo {<|>}",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo<T: Clone> {<|>}",
+"struct Foo<T: Clone> {}
+
+impl<T: Clone> Foo<T> {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo<'a, T: Foo<'a>> {<|>}",
+"struct Foo<'a, T: Foo<'a>> {}
+
+impl<'a, T: Foo<'a>> Foo<'a, T> {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo { baz: String <|>}",
+"struct Foo { baz: String }
+
+impl Foo {
+    fn $0new(baz: String) -> Self { Self { baz } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo { baz: String, qux: Vec<i32> <|>}",
+"struct Foo { baz: String, qux: Vec<i32> }
+
+impl Foo {
+    fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
+}
+",
+        );
+
+        // Check that visibility modifiers don't get brought in for fields
+        check_assist(
+            generate_new,
+"struct Foo { pub baz: String, pub qux: Vec<i32> <|>}",
+"struct Foo { pub baz: String, pub qux: Vec<i32> }
+
+impl Foo {
+    fn $0new(baz: String, qux: Vec<i32>) -> Self { Self { baz, qux } }
+}
+",
+        );
+
+        // Check that it reuses existing impls
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {
+    fn qux(&self) {}
+}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+
+    fn qux(&self) {}
+}
+",
+        );
+
+        check_assist(
+            generate_new,
+"struct Foo {<|>}
+
+impl Foo {
+    fn qux(&self) {}
+    fn baz() -> i32 {
+        5
+    }
+}
+",
+"struct Foo {}
+
+impl Foo {
+    fn $0new() -> Self { Self {  } }
+
+    fn qux(&self) {}
+    fn baz() -> i32 {
+        5
+    }
+}
+",
+        );
+
+        // Check visibility of new fn based on struct
+        check_assist(
+            generate_new,
+"pub struct Foo {<|>}",
+"pub struct Foo {}
+
+impl Foo {
+    pub fn $0new() -> Self { Self {  } }
+}
+",
+        );
+        check_assist(
+            generate_new,
+"pub(crate) struct Foo {<|>}",
+"pub(crate) struct Foo {}
+
+impl Foo {
+    pub(crate) fn $0new() -> Self { Self {  } }
+}
+",
+        );
+    }
+
+    #[test]
+    fn generate_new_not_applicable_if_fn_exists() {
+        check_assist_not_applicable(
+            generate_new,
+            "
+struct Foo {<|>}
+
+impl Foo {
+    fn new() -> Self {
+        Self
+    }
+}",
+        );
+
+        check_assist_not_applicable(
+            generate_new,
+            "
+struct Foo {<|>}
+
+impl Foo {
+    fn New() -> Self {
+        Self
+    }
+}",
+        );
+    }
+
+    #[test]
+    fn generate_new_target() {
+        check_assist_target(
+            generate_new,
+            "
+struct SomeThingIrrelevant;
+/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {<|>}
+struct EvenMoreIrrelevant;
+",
+            "/// Has a lifetime parameter
+struct Foo<'a, T: Foo<'a>> {}",
+        );
+    }
+
+    #[test]
+    fn test_unrelated_new() {
+        check_assist(
+            generate_new,
+            r##"
+pub struct AstId<N: AstNode> {
+    file_id: HirFileId,
+    file_ast_id: FileAstId<N>,
+}
+
+impl<N: AstNode> AstId<N> {
+    pub fn new(file_id: HirFileId, file_ast_id: FileAstId<N>) -> AstId<N> {
+        AstId { file_id, file_ast_id }
+    }
+}
+
+pub struct Source<T> {
+    pub file_id: HirFileId,<|>
+    pub ast: T,
+}
+
+impl<T> Source<T> {
+    pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
+        Source { file_id: self.file_id, ast: f(self.ast) }
+    }
+}
+"##,
+            r##"
+pub struct AstId<N: AstNode> {
+    file_id: HirFileId,
+    file_ast_id: FileAstId<N>,
+}
+
+impl<N: AstNode> AstId<N> {
+    pub fn new(file_id: HirFileId, file_ast_id: FileAstId<N>) -> AstId<N> {
+        AstId { file_id, file_ast_id }
+    }
+}
+
+pub struct Source<T> {
+    pub file_id: HirFileId,
+    pub ast: T,
+}
+
+impl<T> Source<T> {
+    pub fn $0new(file_id: HirFileId, ast: T) -> Self { Self { file_id, ast } }
+
+    pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
+        Source { file_id: self.file_id, ast: f(self.ast) }
+    }
+}
+"##,
+        );
+    }
+}