8 files changed, 160 insertions, 84 deletions

diff --git a/crates/ra_assists/src/assist_config.rs b/crates/ra_assists/src/assist_config.rs
new file mode 100644
index 000000000..c0a0226fb
--- /dev/null
+++ b/crates/ra_assists/src/assist_config.rs
@@ -0,0 +1,27 @@
+//! Settings for tweaking assists.
+//!
+//! The fun thing here is `SnippetCap` -- this type can only be created in this
+//! module, and we use to statically check that we only produce snippet
+//! assists if we are allowed to.
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct AssistConfig {
+    pub snippet_cap: Option<SnippetCap>,
+}
+
+impl AssistConfig {
+    pub fn allow_snippets(&mut self, yes: bool) {
+        self.snippet_cap = if yes { Some(SnippetCap { _private: () }) } else { None }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct SnippetCap {
+    _private: (),
+}
+
+impl Default for AssistConfig {
+    fn default() -> Self {
+        AssistConfig { snippet_cap: Some(SnippetCap { _private: () }) }
+    }
+}
diff --git a/crates/ra_assists/src/assist_context.rs b/crates/ra_assists/src/assist_context.rs
index a680f752b..0dcd9df61 100644
--- a/crates/ra_assists/src/assist_context.rs
+++ b/crates/ra_assists/src/assist_context.rs
@@ -15,7 +15,10 @@ use ra_syntax::{
 };
 use ra_text_edit::TextEditBuilder;
 
-use crate::{Assist, AssistId, GroupLabel, ResolvedAssist};
+use crate::{
+    assist_config::{AssistConfig, SnippetCap},
+    Assist, AssistId, GroupLabel, ResolvedAssist,
+};
 
 /// `AssistContext` allows to apply an assist or check if it could be applied.
 ///
@@ -48,6 +51,7 @@ use crate::{Assist, AssistId, GroupLabel, ResolvedAssist};
 /// moment, because the LSP API is pretty awkward in this place, and it's much
 /// easier to just compute the edit eagerly :-)
 pub(crate) struct AssistContext<'a> {
+    pub(crate) config: &'a AssistConfig,
     pub(crate) sema: Semantics<'a, RootDatabase>,
     pub(crate) db: &'a RootDatabase,
     pub(crate) frange: FileRange,
@@ -55,10 +59,14 @@ pub(crate) struct AssistContext<'a> {
 }
 
 impl<'a> AssistContext<'a> {
-    pub fn new(sema: Semantics<'a, RootDatabase>, frange: FileRange) -> AssistContext<'a> {
+    pub(crate) fn new(
+        sema: Semantics<'a, RootDatabase>,
+        config: &'a AssistConfig,
+        frange: FileRange,
+    ) -> AssistContext<'a> {
         let source_file = sema.parse(frange.file_id);
         let db = sema.db;
-        AssistContext { sema, db, frange, source_file }
+        AssistContext { config, sema, db, frange, source_file }
     }
 
     // NB, this ignores active selection.
@@ -165,11 +173,17 @@ pub(crate) struct AssistBuilder {
     edit: TextEditBuilder,
     cursor_position: Option<TextSize>,
     file: FileId,
+    is_snippet: bool,
 }
 
 impl AssistBuilder {
     pub(crate) fn new(file: FileId) -> AssistBuilder {
-        AssistBuilder { edit: TextEditBuilder::default(), cursor_position: None, file }
+        AssistBuilder {
+            edit: TextEditBuilder::default(),
+            cursor_position: None,
+            file,
+            is_snippet: false,
+        }
     }
 
     /// Remove specified `range` of text.
@@ -180,6 +194,16 @@ impl AssistBuilder {
     pub(crate) fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
         self.edit.insert(offset, text.into())
     }
+    /// Append specified `text` at the given `offset`
+    pub(crate) fn insert_snippet(
+        &mut self,
+        _cap: SnippetCap,
+        offset: TextSize,
+        text: impl Into<String>,
+    ) {
+        self.is_snippet = true;
+        self.edit.insert(offset, text.into())
+    }
     /// Replaces specified `range` of text with a given string.
     pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
         self.edit.replace(range, replace_with.into())
@@ -227,7 +251,12 @@ impl AssistBuilder {
         if edit.is_empty() && self.cursor_position.is_none() {
             panic!("Only call `add_assist` if the assist can be applied")
         }
-        SingleFileChange { label: change_label, edit, cursor_position: self.cursor_position }
-            .into_source_change(self.file)
+        let mut res =
+            SingleFileChange { label: change_label, edit, cursor_position: self.cursor_position }
+                .into_source_change(self.file);
+        if self.is_snippet {
+            res.is_snippet = true;
+        }
+        res
     }
 }
diff --git a/crates/ra_assists/src/handlers/add_custom_impl.rs b/crates/ra_assists/src/handlers/add_custom_impl.rs
index 2baeb8607..fa70c8496 100644
--- a/crates/ra_assists/src/handlers/add_custom_impl.rs
+++ b/crates/ra_assists/src/handlers/add_custom_impl.rs
@@ -25,7 +25,7 @@ use crate::{
 // struct S;
 //
 // impl Debug for S {
-//
+//     $0
 // }
 // ```
 pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
@@ -52,7 +52,7 @@ pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<
         format!("Add custom impl `{}` for `{}`", trait_token.text().as_str(), annotated_name);
 
     let target = attr.syntax().text_range();
-    acc.add(AssistId("add_custom_impl"), label, target, |edit| {
+    acc.add(AssistId("add_custom_impl"), label, target, |builder| {
         let new_attr_input = input
             .syntax()
             .descendants_with_tokens()
@@ -63,20 +63,11 @@ pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<
         let has_more_derives = !new_attr_input.is_empty();
         let new_attr_input = new_attr_input.iter().sep_by(", ").surround_with("(", ")").to_string();
 
-        let mut buf = String::new();
-        buf.push_str("\n\nimpl ");
-        buf.push_str(trait_token.text().as_str());
-        buf.push_str(" for ");
-        buf.push_str(annotated_name.as_str());
-        buf.push_str(" {\n");
-
-        let cursor_delta = if has_more_derives {
-            let delta = input.syntax().text_range().len() - TextSize::of(&new_attr_input);
-            edit.replace(input.syntax().text_range(), new_attr_input);
-            delta
+        if has_more_derives {
+            builder.replace(input.syntax().text_range(), new_attr_input);
         } else {
             let attr_range = attr.syntax().text_range();
-            edit.delete(attr_range);
+            builder.delete(attr_range);
 
             let line_break_range = attr
                 .syntax()
@@ -84,14 +75,24 @@ pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<
                 .filter(|t| t.kind() == WHITESPACE)
                 .map(|t| t.text_range())
                 .unwrap_or_else(|| TextRange::new(TextSize::from(0), TextSize::from(0)));
-            edit.delete(line_break_range);
-
-            attr_range.len() + line_break_range.len()
-        };
-
-        edit.set_cursor(start_offset + TextSize::of(&buf) - cursor_delta);
-        buf.push_str("\n}");
-        edit.insert(start_offset, buf);
+            builder.delete(line_break_range);
+        }
+
+        match ctx.config.snippet_cap {
+            Some(cap) => {
+                builder.insert_snippet(
+                    cap,
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n    $0\n}}", trait_token, annotated_name),
+                );
+            }
+            None => {
+                builder.insert(
+                    start_offset,
+                    format!("\n\nimpl {} for {} {{\n\n}}", trait_token, annotated_name),
+                );
+            }
+        }
     })
 }
 
@@ -117,7 +118,7 @@ struct Foo {
 }
 
 impl Debug for Foo {
-<|>
+    $0
 }
             ",
         )
@@ -139,7 +140,7 @@ pub struct Foo {
 }
 
 impl Debug for Foo {
-<|>
+    $0
 }
             ",
         )
@@ -158,7 +159,7 @@ struct Foo {}
 struct Foo {}
 
 impl Debug for Foo {
-<|>
+    $0
 }
             ",
         )
diff --git a/crates/ra_assists/src/handlers/add_derive.rs b/crates/ra_assists/src/handlers/add_derive.rs
index fb08c19e9..b123b8498 100644
--- a/crates/ra_assists/src/handlers/add_derive.rs
+++ b/crates/ra_assists/src/handlers/add_derive.rs
@@ -18,31 +18,37 @@ use crate::{AssistContext, AssistId, Assists};
 // ```
 // ->
 // ```
-// #[derive()]
+// #[derive($0)]
 // struct Point {
 //     x: u32,
 //     y: u32,
 // }
 // ```
 pub(crate) fn add_derive(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let cap = ctx.config.snippet_cap?;
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let node_start = derive_insertion_offset(&nominal)?;
     let target = nominal.syntax().text_range();
-    acc.add(AssistId("add_derive"), "Add `#[derive]`", target, |edit| {
+    acc.add(AssistId("add_derive"), "Add `#[derive]`", target, |builder| {
         let derive_attr = nominal
             .attrs()
             .filter_map(|x| x.as_simple_call())
             .filter(|(name, _arg)| name == "derive")
             .map(|(_name, arg)| arg)
             .next();
-        let offset = match derive_attr {
+        match derive_attr {
             None => {
-                edit.insert(node_start, "#[derive()]\n");
-                node_start + TextSize::of("#[derive(")
+                builder.insert_snippet(cap, node_start, "#[derive($0)]\n");
+            }
+            Some(tt) => {
+                // Just move the cursor.
+                builder.insert_snippet(
+                    cap,
+                    tt.syntax().text_range().end() - TextSize::of(')'),
+                    "$0",
+                )
             }
-            Some(tt) => tt.syntax().text_range().end() - TextSize::of(')'),
         };
-        edit.set_cursor(offset)
     })
 }
 
@@ -66,12 +72,12 @@ mod tests {
         check_assist(
             add_derive,
             "struct Foo { a: i32, <|>}",
-            "#[derive(<|>)]\nstruct Foo { a: i32, }",
+            "#[derive($0)]\nstruct Foo { a: i32, }",
         );
         check_assist(
             add_derive,
             "struct Foo { <|> a: i32, }",
-            "#[derive(<|>)]\nstruct Foo {  a: i32, }",
+            "#[derive($0)]\nstruct Foo {  a: i32, }",
         );
     }
 
@@ -80,7 +86,7 @@ mod tests {
         check_assist(
             add_derive,
             "#[derive(Clone)]\nstruct Foo { a: i32<|>, }",
-            "#[derive(Clone<|>)]\nstruct Foo { a: i32, }",
+            "#[derive(Clone$0)]\nstruct Foo { a: i32, }",
         );
     }
 
@@ -96,7 +102,7 @@ struct Foo { a: i32<|>, }
             "
 /// `Foo` is a pretty important struct.
 /// It does stuff.
-#[derive(<|>)]
+#[derive($0)]
 struct Foo { a: i32, }
             ",
         );
diff --git a/crates/ra_assists/src/handlers/add_impl.rs b/crates/ra_assists/src/handlers/add_impl.rs
index df114a0d8..eceba7d0a 100644
--- a/crates/ra_assists/src/handlers/add_impl.rs
+++ b/crates/ra_assists/src/handlers/add_impl.rs
@@ -1,7 +1,4 @@
-use ra_syntax::{
-    ast::{self, AstNode, NameOwner, TypeParamsOwner},
-    TextSize,
-};
+use ra_syntax::ast::{self, AstNode, NameOwner, TypeParamsOwner};
 use stdx::{format_to, SepBy};
 
 use crate::{AssistContext, AssistId, Assists};
@@ -12,17 +9,17 @@ use crate::{AssistContext, AssistId, Assists};
 //
 // ```
 // struct Ctx<T: Clone> {
-//      data: T,<|>
+//     data: T,<|>
 // }
 // ```
 // ->
 // ```
 // struct Ctx<T: Clone> {
-//      data: T,
+//     data: T,
 // }
 //
 // impl<T: Clone> Ctx<T> {
-//
+//     $0
 // }
 // ```
 pub(crate) fn add_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
@@ -50,30 +47,37 @@ pub(crate) fn add_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
             let generic_params = lifetime_params.chain(type_params).sep_by(", ");
             format_to!(buf, "<{}>", generic_params)
         }
-        buf.push_str(" {\n");
-        edit.set_cursor(start_offset + TextSize::of(&buf));
-        buf.push_str("\n}");
-        edit.insert(start_offset, buf);
+        match ctx.config.snippet_cap {
+            Some(cap) => {
+                buf.push_str(" {\n    $0\n}");
+                edit.insert_snippet(cap, start_offset, buf);
+            }
+            None => {
+                buf.push_str(" {\n}");
+                edit.insert(start_offset, buf);
+            }
+        }
     })
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use crate::tests::{check_assist, check_assist_target};
 
+    use super::*;
+
     #[test]
     fn test_add_impl() {
-        check_assist(add_impl, "struct Foo {<|>}\n", "struct Foo {}\n\nimpl Foo {\n<|>\n}\n");
+        check_assist(add_impl, "struct Foo {<|>}\n", "struct Foo {}\n\nimpl Foo {\n    $0\n}\n");
         check_assist(
             add_impl,
             "struct Foo<T: Clone> {<|>}",
-            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n<|>\n}",
+            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n    $0\n}",
         );
         check_assist(
             add_impl,
             "struct Foo<'a, T: Foo<'a>> {<|>}",
-            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n<|>\n}",
+            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n    $0\n}",
         );
     }
 
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index b6dc7cb1b..7f0a723c9 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -10,6 +10,7 @@ macro_rules! eprintln {
     ($($tt:tt)*) => { stdx::eprintln!($($tt)*) };
 }
 
+mod assist_config;
 mod assist_context;
 mod marks;
 #[cfg(test)]
@@ -24,6 +25,8 @@ use ra_syntax::TextRange;
 
 pub(crate) use crate::assist_context::{AssistContext, Assists};
 
+pub use assist_config::AssistConfig;
+
 /// Unique identifier of the assist, should not be shown to the user
 /// directly.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -54,9 +57,9 @@ impl Assist {
     ///
     /// Assists are returned in the "unresolved" state, that is only labels are
     /// returned, without actual edits.
-    pub fn unresolved(db: &RootDatabase, range: FileRange) -> Vec<Assist> {
+    pub fn unresolved(db: &RootDatabase, config: &AssistConfig, range: FileRange) -> Vec<Assist> {
         let sema = Semantics::new(db);
-        let ctx = AssistContext::new(sema, range);
+        let ctx = AssistContext::new(sema, config, range);
         let mut acc = Assists::new_unresolved(&ctx);
         handlers::all().iter().for_each(|handler| {
             handler(&mut acc, &ctx);
@@ -68,9 +71,13 @@ impl Assist {
     ///
     /// Assists are returned in the "resolved" state, that is with edit fully
     /// computed.
-    pub fn resolved(db: &RootDatabase, range: FileRange) -> Vec<ResolvedAssist> {
+    pub fn resolved(
+        db: &RootDatabase,
+        config: &AssistConfig,
+        range: FileRange,
+    ) -> Vec<ResolvedAssist> {
         let sema = Semantics::new(db);
-        let ctx = AssistContext::new(sema, range);
+        let ctx = AssistContext::new(sema, config, range);
         let mut acc = Assists::new_resolved(&ctx);
         handlers::all().iter().for_each(|handler| {
             handler(&mut acc, &ctx);
diff --git a/crates/ra_assists/src/tests.rs b/crates/ra_assists/src/tests.rs
index a3eacb8f1..9ba3da786 100644
--- a/crates/ra_assists/src/tests.rs
+++ b/crates/ra_assists/src/tests.rs
@@ -11,7 +11,7 @@ use test_utils::{
     RangeOrOffset,
 };
 
-use crate::{handlers::Handler, Assist, AssistContext, Assists};
+use crate::{handlers::Handler, Assist, AssistConfig, AssistContext, Assists};
 
 pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
     let (mut db, file_id) = RootDatabase::with_single_file(text);
@@ -41,14 +41,14 @@ fn check_doc_test(assist_id: &str, before: &str, after: &str) {
     let (db, file_id) = crate::tests::with_single_file(&before);
     let frange = FileRange { file_id, range: selection.into() };
 
-    let mut assist = Assist::resolved(&db, frange)
+    let mut assist = Assist::resolved(&db, &AssistConfig::default(), frange)
         .into_iter()
         .find(|assist| assist.assist.id.0 == assist_id)
         .unwrap_or_else(|| {
             panic!(
                 "\n\nAssist is not applicable: {}\nAvailable assists: {}",
                 assist_id,
-                Assist::resolved(&db, frange)
+                Assist::resolved(&db, &AssistConfig::default(), frange)
                     .into_iter()
                     .map(|assist| assist.assist.id.0)
                     .collect::<Vec<_>>()
@@ -90,7 +90,8 @@ fn check(handler: Handler, before: &str, expected: ExpectedResult) {
     let frange = FileRange { file_id: file_with_caret_id, range: range_or_offset.into() };
 
     let sema = Semantics::new(&db);
-    let ctx = AssistContext::new(sema, frange);
+    let config = AssistConfig::default();
+    let ctx = AssistContext::new(sema, &config, frange);
     let mut acc = Assists::new_resolved(&ctx);
     handler(&mut acc, &ctx);
     let mut res = acc.finish_resolved();
@@ -103,19 +104,20 @@ fn check(handler: Handler, before: &str, expected: ExpectedResult) {
             let mut actual = db.file_text(change.file_id).as_ref().to_owned();
             change.edit.apply(&mut actual);
 
-            match source_change.cursor_position {
-                None => {
-                    if let RangeOrOffset::Offset(before_cursor_pos) = range_or_offset {
-                        let off = change
-                            .edit
-                            .apply_to_offset(before_cursor_pos)
-                            .expect("cursor position is affected by the edit");
-                        actual = add_cursor(&actual, off)
+            if !source_change.is_snippet {
+                match source_change.cursor_position {
+                    None => {
+                        if let RangeOrOffset::Offset(before_cursor_pos) = range_or_offset {
+                            let off = change
+                                .edit
+                                .apply_to_offset(before_cursor_pos)
+                                .expect("cursor position is affected by the edit");
+                            actual = add_cursor(&actual, off)
+                        }
                     }
-                }
-                Some(off) => actual = add_cursor(&actual, off.offset),
-            };
-
+                    Some(off) => actual = add_cursor(&actual, off.offset),
+                };
+            }
             assert_eq_text!(after, &actual);
         }
         (Some(assist), ExpectedResult::Target(target)) => {
@@ -136,7 +138,7 @@ fn assist_order_field_struct() {
     let (before_cursor_pos, before) = extract_offset(before);
     let (db, file_id) = with_single_file(&before);
     let frange = FileRange { file_id, range: TextRange::empty(before_cursor_pos) };
-    let assists = Assist::resolved(&db, frange);
+    let assists = Assist::resolved(&db, &AssistConfig::default(), frange);
     let mut assists = assists.iter();
 
     assert_eq!(
@@ -159,7 +161,7 @@ fn assist_order_if_expr() {
     let (range, before) = extract_range(before);
     let (db, file_id) = with_single_file(&before);
     let frange = FileRange { file_id, range };
-    let assists = Assist::resolved(&db, frange);
+    let assists = Assist::resolved(&db, &AssistConfig::default(), frange);
     let mut assists = assists.iter();
 
     assert_eq!(assists.next().expect("expected assist").assist.label, "Extract into variable");
diff --git a/crates/ra_assists/src/tests/generated.rs b/crates/ra_assists/src/tests/generated.rs
index 972dbd251..9487c9239 100644
--- a/crates/ra_assists/src/tests/generated.rs
+++ b/crates/ra_assists/src/tests/generated.rs
@@ -15,7 +15,7 @@ struct S;
 struct S;
 
 impl Debug for S {
-
+    $0
 }
 "#####,
     )
@@ -32,7 +32,7 @@ struct Point {
 }
 "#####,
         r#####"
-#[derive()]
+#[derive($0)]
 struct Point {
     x: u32,
     y: u32,
@@ -108,16 +108,16 @@ fn doctest_add_impl() {
         "add_impl",
         r#####"
 struct Ctx<T: Clone> {
-     data: T,<|>
+    data: T,<|>
 }
 "#####,
         r#####"
 struct Ctx<T: Clone> {
-     data: T,
+    data: T,
 }
 
 impl<T: Clone> Ctx<T> {
-
+    $0
 }
 "#####,
     )