1 files changed, 200 insertions, 0 deletions

diff --git a/crates/ra_assists/src/handlers/generate_from_impl_for_enum.rs b/crates/ra_assists/src/handlers/generate_from_impl_for_enum.rs
new file mode 100644
index 000000000..e781be61e
--- /dev/null
+++ b/crates/ra_assists/src/handlers/generate_from_impl_for_enum.rs
@@ -0,0 +1,200 @@
+use ra_ide_db::RootDatabase;
+use ra_syntax::ast::{self, AstNode, NameOwner};
+use test_utils::mark;
+
+use crate::{utils::FamousDefs, AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: generate_from_impl_for_enum
+//
+// Adds a From impl for an enum variant with one tuple field.
+//
+// ```
+// enum A { <|>One(u32) }
+// ```
+// ->
+// ```
+// enum A { One(u32) }
+//
+// impl From<u32> for A {
+//     fn from(v: u32) -> Self {
+//         A::One(v)
+//     }
+// }
+// ```
+pub(crate) fn generate_from_impl_for_enum(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let variant = ctx.find_node_at_offset::<ast::EnumVariant>()?;
+    let variant_name = variant.name()?;
+    let enum_name = variant.parent_enum().name()?;
+    let field_list = match variant.kind() {
+        ast::StructKind::Tuple(field_list) => field_list,
+        _ => return None,
+    };
+    if field_list.fields().count() != 1 {
+        return None;
+    }
+    let field_type = field_list.fields().next()?.type_ref()?;
+    let path = match field_type {
+        ast::TypeRef::PathType(it) => it,
+        _ => return None,
+    };
+
+    if existing_from_impl(&ctx.sema, &variant).is_some() {
+        mark::hit!(test_add_from_impl_already_exists);
+        return None;
+    }
+
+    let target = variant.syntax().text_range();
+    acc.add(
+        AssistId("generate_from_impl_for_enum", AssistKind::Refactor),
+        "Generate `From` impl for this enum variant",
+        target,
+        |edit| {
+            let start_offset = variant.parent_enum().syntax().text_range().end();
+            let buf = format!(
+                r#"
+
+impl From<{0}> for {1} {{
+    fn from(v: {0}) -> Self {{
+        {1}::{2}(v)
+    }}
+}}"#,
+                path.syntax(),
+                enum_name,
+                variant_name
+            );
+            edit.insert(start_offset, buf);
+        },
+    )
+}
+
+fn existing_from_impl(
+    sema: &'_ hir::Semantics<'_, RootDatabase>,
+    variant: &ast::EnumVariant,
+) -> Option<()> {
+    let variant = sema.to_def(variant)?;
+    let enum_ = variant.parent_enum(sema.db);
+    let krate = enum_.module(sema.db).krate();
+
+    let from_trait = FamousDefs(sema, krate).core_convert_From()?;
+
+    let enum_type = enum_.ty(sema.db);
+
+    let wrapped_type = variant.fields(sema.db).get(0)?.signature_ty(sema.db);
+
+    if enum_type.impls_trait(sema.db, from_trait, &[wrapped_type]) {
+        Some(())
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_generate_from_impl_for_enum() {
+        check_assist(
+            generate_from_impl_for_enum,
+            "enum A { <|>One(u32) }",
+            r#"enum A { One(u32) }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_from_impl_for_enum_complicated_path() {
+        check_assist(
+            generate_from_impl_for_enum,
+            r#"enum A { <|>One(foo::bar::baz::Boo) }"#,
+            r#"enum A { One(foo::bar::baz::Boo) }
+
+impl From<foo::bar::baz::Boo> for A {
+    fn from(v: foo::bar::baz::Boo) -> Self {
+        A::One(v)
+    }
+}"#,
+        );
+    }
+
+    fn check_not_applicable(ra_fixture: &str) {
+        let fixture =
+            format!("//- /main.rs crate:main deps:core\n{}\n{}", ra_fixture, FamousDefs::FIXTURE);
+        check_assist_not_applicable(generate_from_impl_for_enum, &fixture)
+    }
+
+    #[test]
+    fn test_add_from_impl_no_element() {
+        check_not_applicable("enum A { <|>One }");
+    }
+
+    #[test]
+    fn test_add_from_impl_more_than_one_element_in_tuple() {
+        check_not_applicable("enum A { <|>One(u32, String) }");
+    }
+
+    #[test]
+    fn test_add_from_impl_struct_variant() {
+        check_not_applicable("enum A { <|>One { x: u32 } }");
+    }
+
+    #[test]
+    fn test_add_from_impl_already_exists() {
+        mark::check!(test_add_from_impl_already_exists);
+        check_not_applicable(
+            r#"
+enum A { <|>One(u32), }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_add_from_impl_different_variant_impl_exists() {
+        check_assist(
+            generate_from_impl_for_enum,
+            r#"enum A { <|>One(u32), Two(String), }
+
+impl From<String> for A {
+    fn from(v: String) -> Self {
+        A::Two(v)
+    }
+}
+
+pub trait From<T> {
+    fn from(T) -> Self;
+}"#,
+            r#"enum A { One(u32), Two(String), }
+
+impl From<u32> for A {
+    fn from(v: u32) -> Self {
+        A::One(v)
+    }
+}
+
+impl From<String> for A {
+    fn from(v: String) -> Self {
+        A::Two(v)
+    }
+}
+
+pub trait From<T> {
+    fn from(T) -> Self;
+}"#,
+        );
+    }
+}