Merge #989

989: Implement naive version of fill_struct_fields assist r=matklad a=yanchith

Fixes #964

This implements the `fill_struct_fields` assist. Currently only works for named struct fields, but not for tuple structs, because we seem to be missing a `TupleStructLit` (akin to `StructLit`, but for tuple structs). I am happy to implement `TupleStructLit` parsing given some guidance (provided it's really missing) and make the assist work for tuple structs as well. Could do so either in this PR, or another one 🙂 

Sorry if I missed something important, this is my first PR for Rust Analyzer.

Btw is there any way to run the assists in emacs?

UPDATE: I just realized that parsing `TupleStructLit` would be quite difficult as it it really similar, if not identical to a function call...

Co-authored-by: yanchith <yanchi.toth@gmail.com>

crates/ra_assists/src/fill_struct_fields.rs

@@ -0,0 +1,151 @@
+use std::fmt::Write;
+
+use hir::{AdtDef, Ty, source_binder};
+use hir::db::HirDatabase;
+
+use ra_syntax::ast::{self, AstNode};
+
+use crate::{AssistCtx, Assist, AssistId};
+
+pub(crate) fn fill_struct_fields(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let struct_lit = ctx.node_at_offset::<ast::StructLit>()?;
+    let named_field_list = struct_lit.named_field_list()?;
+
+    // If we already have existing struct fields, don't provide the assist.
+    if named_field_list.fields().count() > 0 {
+        return None;
+    }
+
+    let function =
+        source_binder::function_from_child_node(ctx.db, ctx.frange.file_id, struct_lit.syntax())?;
+
+    let infer_result = function.infer(ctx.db);
+    let source_map = function.body_source_map(ctx.db);
+    let node_expr = source_map.node_expr(struct_lit.into())?;
+    let struct_lit_ty = infer_result[node_expr].clone();
+    let struct_def = match struct_lit_ty {
+        Ty::Adt { def_id: AdtDef::Struct(s), .. } => s,
+        _ => return None,
+    };
+
+    let db = ctx.db;
+    ctx.add_action(AssistId("fill_struct_fields"), "fill struct fields", |edit| {
+        let mut buf = String::from("{\n");
+        let struct_fields = struct_def.fields(db);
+        for field in struct_fields {
+            let field_name = field.name(db).to_string();
+            write!(&mut buf, "    {}: (),\n", field_name).unwrap();
+        }
+        buf.push_str("}");
+
+        edit.target(struct_lit.syntax().range());
+        edit.set_cursor(struct_lit.syntax().range().start());
+        edit.replace_node_and_indent(named_field_list.syntax(), buf);
+    });
+
+    ctx.build()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::helpers::{check_assist, check_assist_target};
+
+    use super::fill_struct_fields;
+
+    #[test]
+    fn fill_struct_fields_empty_body() {
+        check_assist(
+            fill_struct_fields,
+            r#"
+            struct S<'a, D> {
+                a: u32,
+                b: String,
+                c: (i32, i32),
+                d: D,
+                r: &'a str,
+            }
+
+            fn main() {
+                let s = S<|> {}
+            }
+            "#,
+            r#"
+            struct S<'a, D> {
+                a: u32,
+                b: String,
+                c: (i32, i32),
+                d: D,
+                r: &'a str,
+            }
+
+            fn main() {
+                let s = <|>S {
+                    a: (),
+                    b: (),
+                    c: (),
+                    d: (),
+                    r: (),
+                }
+            }
+            "#,
+        );
+    }
+
+    #[test]
+    fn fill_struct_fields_target() {
+        check_assist_target(
+            fill_struct_fields,
+            r#"
+            struct S<'a, D> {
+                a: u32,
+                b: String,
+                c: (i32, i32),
+                d: D,
+                r: &'a str,
+            }
+
+            fn main() {
+                let s = S<|> {}
+            }
+            "#,
+            "S {}",
+        );
+    }
+
+    #[test]
+    fn fill_struct_fields_preserve_self() {
+        check_assist(
+            fill_struct_fields,
+            r#"
+            struct Foo {
+                foo: u8,
+                bar: String,
+                baz: i128,
+            }
+
+            impl Foo {
+                pub fn new() -> Self {
+                    Self <|>{}
+                }
+            }
+            "#,
+            r#"
+            struct Foo {
+                foo: u8,
+                bar: String,
+                baz: i128,
+            }
+
+            impl Foo {
+                pub fn new() -> Self {
+                    <|>Self {
+                        foo: (),
+                        bar: (),
+                        baz: (),
+                    }
+                }
+            }
+            "#,
+        );
+    }
+}

crates/ra_assists/src/lib.rs

@@ -90,6 +90,7 @@ mod add_impl;
 mod flip_comma;
 mod change_visibility;
 mod fill_match_arms;
+mod fill_struct_fields;
 mod introduce_variable;
 mod replace_if_let_with_match;
 mod split_import;
@@ -103,6 +104,7 @@ fn all_assists<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assis
         add_impl::add_impl,
         change_visibility::change_visibility,
         fill_match_arms::fill_match_arms,
+        fill_struct_fields::fill_struct_fields,
         flip_comma::flip_comma,
         introduce_variable::introduce_variable,
         replace_if_let_with_match::replace_if_let_with_match,