3 files changed, 197 insertions, 0 deletions

diff --git a/crates/ra_ide_api/src/assists/fill_match_arm.rs b/crates/ra_ide_api/src/assists/fill_match_arm.rs
new file mode 100644
index 000000000..6ae829d85
--- /dev/null
+++ b/crates/ra_ide_api/src/assists/fill_match_arm.rs
@@ -0,0 +1,157 @@
+use std::fmt::Write;
+use hir::{
+    AdtDef,
+    source_binder,
+    Ty,
+    FieldSource,
+};
+use ra_ide_api_light::{
+    assists::{
+        Assist,
+        AssistBuilder
+    }
+};
+use ra_syntax::{
+    ast::{
+        self,
+        AstNode,
+    }
+};
+
+use crate::assists::AssistCtx;
+
+pub fn fill_match_arm(ctx: AssistCtx) -> Option<Assist> {
+    let match_expr = ctx.node_at_offset::<ast::MatchExpr>()?;
+
+    // We already have some match arms, so we don't provide any assists.
+    match match_expr.match_arm_list() {
+        Some(arm_list) if arm_list.arms().count() > 0 => {
+            return None;
+        }
+        _ => {}
+    }
+
+    let expr = match_expr.expr()?;
+    let function = source_binder::function_from_child_node(ctx.db, ctx.file_id, expr.syntax())?;
+    let infer_result = function.infer(ctx.db);
+    let syntax_mapping = function.body_syntax_mapping(ctx.db);
+    let node_expr = syntax_mapping.node_expr(expr)?;
+    let match_expr_ty = infer_result[node_expr].clone();
+    match match_expr_ty {
+        Ty::Adt { def_id, .. } => match def_id {
+            AdtDef::Enum(e) => {
+                let mut buf = format!("match {} {{\n", expr.syntax().text().to_string());
+                let variants = e.variants(ctx.db);
+                for variant in variants {
+                    let name = variant.name(ctx.db)?;
+                    write!(
+                        &mut buf,
+                        "    {}::{}",
+                        e.name(ctx.db)?.to_string(),
+                        name.to_string()
+                    )
+                    .expect("write fmt");
+
+                    let pat = variant
+                        .fields(ctx.db)
+                        .into_iter()
+                        .map(|field| {
+                            let name = field.name(ctx.db).to_string();
+                            let (_, source) = field.source(ctx.db);
+                            match source {
+                                FieldSource::Named(_) => name,
+                                FieldSource::Pos(_) => "_".to_string(),
+                            }
+                        })
+                        .collect::<Vec<_>>();
+
+                    match pat.first().map(|s| s.as_str()) {
+                        Some("_") => write!(&mut buf, "({})", pat.join(", ")).expect("write fmt"),
+                        Some(_) => write!(&mut buf, "{{{}}}", pat.join(", ")).expect("write fmt"),
+                        None => (),
+                    };
+
+                    buf.push_str(" => (),\n");
+                }
+                buf.push_str("}");
+                ctx.build("fill match arms", |edit: &mut AssistBuilder| {
+                    edit.replace_node_and_indent(match_expr.syntax(), buf);
+                })
+            }
+            _ => None,
+        },
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use insta::assert_debug_snapshot_matches;
+
+    use ra_syntax::{TextRange, TextUnit};
+
+    use crate::{
+        FileRange,
+        mock_analysis::{analysis_and_position, single_file_with_position}
+};
+    use ra_db::SourceDatabase;
+
+    fn test_assit(name: &str, code: &str) {
+        let (analysis, position) = if code.contains("//-") {
+            analysis_and_position(code)
+        } else {
+            single_file_with_position(code)
+        };
+        let frange = FileRange {
+            file_id: position.file_id,
+            range: TextRange::offset_len(position.offset, TextUnit::from(1)),
+        };
+        let source_file = analysis
+            .with_db(|db| db.parse(frange.file_id))
+            .expect("source file");
+        let ret = analysis
+            .with_db(|db| crate::assists::assists(db, frange.file_id, &source_file, frange.range))
+            .expect("assists");
+
+        assert_debug_snapshot_matches!(name, ret);
+    }
+
+    #[test]
+    fn test_fill_match_arm() {
+        test_assit(
+            "fill_match_arm1",
+            r#"
+        enum A {
+            As,
+            Bs,
+            Cs(String),
+            Ds(String, String),
+            Es{x: usize, y: usize}
+        }
+
+        fn main() {
+            let a = A::As;
+            match a<|>
+        }
+        "#,
+        );
+
+        test_assit(
+            "fill_match_arm2",
+            r#"
+        enum A {
+            As,
+            Bs,
+            Cs(String),
+            Ds(String, String),
+            Es{x: usize, y: usize}
+        }
+
+        fn main() {
+            let a = A::As;
+            match a<|> {}
+        }
+        "#,
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm1.snap b/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm1.snap
new file mode 100644
index 000000000..980726d92
--- /dev/null
+++ b/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm1.snap
@@ -0,0 +1,20 @@
+---
+created: "2019-02-03T15:38:46.094184+00:00"
+creator: [email protected]
+expression: ret
+source: crates/ra_ide_api/src/assits/fill_match_arm.rs
+---
+[
+    LocalEdit {
+        label: "fill match arms",
+        edit: TextEdit {
+            atoms: [
+                AtomTextEdit {
+                    delete: [211; 218),
+                    insert: "match a {\n                A::As => (),\n                A::Bs => (),\n                A::Cs(_) => (),\n                A::Ds(_, _) => (),\n                A::Es{x, y} => (),\n            }"
+                }
+            ]
+        },
+        cursor_position: None
+    }
+]
diff --git a/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm2.snap b/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm2.snap
new file mode 100644
index 000000000..cee0efe74
--- /dev/null
+++ b/crates/ra_ide_api/src/assists/snapshots/tests__fill_match_arm2.snap
@@ -0,0 +1,20 @@
+---
+created: "2019-02-03T15:41:34.640074+00:00"
+creator: [email protected]
+expression: ret
+source: crates/ra_ide_api/src/assits/fill_match_arm.rs
+---
+[
+    LocalEdit {
+        label: "fill match arms",
+        edit: TextEdit {
+            atoms: [
+                AtomTextEdit {
+                    delete: [211; 221),
+                    insert: "match a {\n                A::As => (),\n                A::Bs => (),\n                A::Cs(_) => (),\n                A::Ds(_, _) => (),\n                A::Es{x, y} => (),\n            }"
+                }
+            ]
+        },
+        cursor_position: None
+    }
+]