1 files changed, 162 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/generate_setter.rs b/crates/assists/src/handlers/generate_setter.rs
new file mode 100644
index 000000000..c9043a162
--- /dev/null
+++ b/crates/assists/src/handlers/generate_setter.rs
@@ -0,0 +1,162 @@
+use stdx::{format_to, to_lower_snake_case};
+use syntax::ast::VisibilityOwner;
+use syntax::ast::{self, AstNode, NameOwner};
+
+use crate::{
+    utils::{find_impl_block, find_struct_impl, generate_impl_text},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: generate_setter
+//
+// Generate a setter method.
+//
+// ```
+// struct Person {
+//     nam$0e: String,
+// }
+// ```
+// ->
+// ```
+// struct Person {
+//     name: String,
+// }
+//
+// impl Person {
+//     /// Set the person's name.
+//     fn set_name(&mut self, name: String) {
+//         self.name = name;
+//     }
+// }
+// ```
+pub(crate) fn generate_setter(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let strukt = ctx.find_node_at_offset::<ast::Struct>()?;
+    let field = ctx.find_node_at_offset::<ast::RecordField>()?;
+
+    let strukt_name = strukt.name()?;
+    let field_name = field.name()?;
+    let field_ty = field.ty()?;
+
+    // Return early if we've found an existing fn
+    let fn_name = to_lower_snake_case(&field_name.to_string());
+    let impl_def = find_struct_impl(
+        &ctx,
+        &ast::Adt::Struct(strukt.clone()),
+        format!("set_{}", fn_name).as_str(),
+    )?;
+
+    let target = field.syntax().text_range();
+    acc.add(
+        AssistId("generate_setter", AssistKind::Generate),
+        "Generate a setter method",
+        target,
+        |builder| {
+            let mut buf = String::with_capacity(512);
+
+            let fn_name_spaced = fn_name.replace('_', " ");
+            let strukt_name_spaced =
+                to_lower_snake_case(&strukt_name.to_string()).replace('_', " ");
+
+            if impl_def.is_some() {
+                buf.push('\n');
+            }
+
+            let vis = strukt.visibility().map_or(String::new(), |v| format!("{} ", v));
+            format_to!(
+                buf,
+                "    /// Set the {}'s {}.
+    {}fn set_{}(&mut self, {}: {}) {{
+        self.{} = {};
+    }}",
+                strukt_name_spaced,
+                fn_name_spaced,
+                vis,
+                fn_name,
+                fn_name,
+                field_ty,
+                fn_name,
+                fn_name,
+            );
+
+            let start_offset = impl_def
+                .and_then(|impl_def| find_impl_block(impl_def, &mut buf))
+                .unwrap_or_else(|| {
+                    buf = generate_impl_text(&ast::Adt::Struct(strukt.clone()), &buf);
+                    strukt.syntax().text_range().end()
+                });
+
+            builder.insert(start_offset, buf);
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    fn check_not_applicable(ra_fixture: &str) {
+        check_assist_not_applicable(generate_setter, ra_fixture)
+    }
+
+    #[test]
+    fn test_generate_setter_from_field() {
+        check_assist(
+            generate_setter,
+            r#"
+struct Person<T: Clone> {
+    dat$0a: T,
+}"#,
+            r#"
+struct Person<T: Clone> {
+    data: T,
+}
+
+impl<T: Clone> Person<T> {
+    /// Set the person's data.
+    fn set_data(&mut self, data: T) {
+        self.data = data;
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_setter_already_implemented() {
+        check_not_applicable(
+            r#"
+struct Person<T: Clone> {
+    dat$0a: T,
+}
+
+impl<T: Clone> Person<T> {
+    fn set_data(&mut self, data: T) {
+        self.data = data;
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_setter_from_field_with_visibility_marker() {
+        check_assist(
+            generate_setter,
+            r#"
+pub(crate) struct Person<T: Clone> {
+    dat$0a: T,
+}"#,
+            r#"
+pub(crate) struct Person<T: Clone> {
+    data: T,
+}
+
+impl<T: Clone> Person<T> {
+    /// Set the person's data.
+    pub(crate) fn set_data(&mut self, data: T) {
+        self.data = data;
+    }
+}"#,
+        );
+    }
+}