diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index c527366791..c5e9056afb 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -82,12 +82,12 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
         f(ctx)
     }
 
-    pub(crate) fn add_action(
-        &mut self,
+    pub(crate) fn add_assist(
+        mut self,
         id: AssistId,
         label: impl Into<String>,
         f: impl FnOnce(&mut AssistBuilder),
-    ) -> &mut Self {
+    ) -> Option<Assist> {
         let label = AssistLabel { label: label.into(), id };
         match &mut self.assist {
             Assist::Unresolved(labels) => labels.push(label),
@@ -100,10 +100,6 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
                 labels_actions.push((label, action));
             }
         }
-        self
-    }
-
-    pub(crate) fn build(self) -> Option<Assist> {
         Some(self.assist)
     }
 
diff --git a/crates/ra_assists/src/assists/add_derive.rs b/crates/ra_assists/src/assists/add_derive.rs
index d1e925b71f..764b17bd8d 100644
--- a/crates/ra_assists/src/assists/add_derive.rs
+++ b/crates/ra_assists/src/assists/add_derive.rs
@@ -25,10 +25,10 @@ use crate::{Assist, AssistCtx, AssistId};
 //     y: u32,
 // }
 // ```
-pub(crate) fn add_derive(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_derive(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let node_start = derive_insertion_offset(&nominal)?;
-    ctx.add_action(AssistId("add_derive"), "add `#[derive]`", |edit| {
+    ctx.add_assist(AssistId("add_derive"), "add `#[derive]`", |edit| {
         let derive_attr = nominal
             .attrs()
             .filter_map(|x| x.as_simple_call())
@@ -44,9 +44,7 @@ pub(crate) fn add_derive(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
         };
         edit.target(nominal.syntax().text_range());
         edit.set_cursor(offset)
-    });
-
-    ctx.build()
+    })
 }
 
 // Insert `derive` after doc comments.
diff --git a/crates/ra_assists/src/assists/add_explicit_type.rs b/crates/ra_assists/src/assists/add_explicit_type.rs
index ffbdc0b629..ddda1a0f2c 100644
--- a/crates/ra_assists/src/assists/add_explicit_type.rs
+++ b/crates/ra_assists/src/assists/add_explicit_type.rs
@@ -21,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let x: i32 = 92;
 // }
 // ```
-pub(crate) fn add_explicit_type(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_explicit_type(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let stmt = ctx.find_node_at_offset::<LetStmt>()?;
     let expr = stmt.initializer()?;
     let pat = stmt.pat()?;
@@ -47,11 +47,10 @@ pub(crate) fn add_explicit_type(mut ctx: AssistCtx<impl HirDatabase>) -> Option<
         return None;
     }
 
-    ctx.add_action(AssistId("add_explicit_type"), "add explicit type", |edit| {
+    ctx.add_assist(AssistId("add_explicit_type"), "add explicit type", |edit| {
         edit.target(pat_range);
         edit.insert(name_range.end(), format!(": {}", ty.display(db)));
-    });
-    ctx.build()
+    })
 }
 
 /// Returns true if any type parameter is unknown
diff --git a/crates/ra_assists/src/assists/add_impl.rs b/crates/ra_assists/src/assists/add_impl.rs
index fd3588d249..7da0cfd0d3 100644
--- a/crates/ra_assists/src/assists/add_impl.rs
+++ b/crates/ra_assists/src/assists/add_impl.rs
@@ -27,10 +27,10 @@ use crate::{Assist, AssistCtx, AssistId};
 //
 // }
 // ```
-pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_impl(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let name = nominal.name()?;
-    ctx.add_action(AssistId("add_impl"), "add impl", |edit| {
+    ctx.add_assist(AssistId("add_impl"), "add impl", |edit| {
         edit.target(nominal.syntax().text_range());
         let type_params = nominal.type_param_list();
         let start_offset = nominal.syntax().text_range().end();
@@ -54,9 +54,7 @@ pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
         edit.set_cursor(start_offset + TextUnit::of_str(&buf));
         buf.push_str("\n}");
         edit.insert(start_offset, buf);
-    });
-
-    ctx.build()
+    })
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/add_import.rs b/crates/ra_assists/src/assists/add_import.rs
index 7aa66b1fec..c522d6a5a7 100644
--- a/crates/ra_assists/src/assists/add_import.rs
+++ b/crates/ra_assists/src/assists/add_import.rs
@@ -39,7 +39,7 @@ pub fn auto_import_text_edit(
     }
 }
 
-pub(crate) fn add_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let path: ast::Path = ctx.find_node_at_offset()?;
     // We don't want to mess with use statements
     if path.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
@@ -53,7 +53,7 @@ pub(crate) fn add_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
     }
 
     let module = path.syntax().ancestors().find_map(ast::Module::cast);
-    let anchor = match module.and_then(|it| it.item_list()) {
+    let position = match module.and_then(|it| it.item_list()) {
         Some(item_list) => item_list.syntax().clone(),
         None => {
             let current_file = path.syntax().ancestors().find_map(ast::SourceFile::cast)?;
@@ -61,11 +61,9 @@ pub(crate) fn add_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
         }
     };
 
-    ctx.add_action(AssistId("add_import"), format!("import {}", fmt_segments(&segments)), |edit| {
-        apply_auto_import(&anchor, &path, &segments, edit.text_edit_builder());
-    });
-
-    ctx.build()
+    ctx.add_assist(AssistId("add_import"), format!("import {}", fmt_segments(&segments)), |edit| {
+        apply_auto_import(&position, &path, &segments, edit.text_edit_builder());
+    })
 }
 
 fn collect_path_segments_raw(
diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index 2585f30454..41de239219 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -91,7 +91,7 @@ pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> O
 }
 
 fn add_missing_impl_members_inner(
-    mut ctx: AssistCtx<impl HirDatabase>,
+    ctx: AssistCtx<impl HirDatabase>,
     mode: AddMissingImplMembersMode,
     assist_id: &'static str,
     label: &'static str,
@@ -133,7 +133,7 @@ fn add_missing_impl_members_inner(
         return None;
     }
 
-    ctx.add_action(AssistId(assist_id), label, |edit| {
+    ctx.add_assist(AssistId(assist_id), label, |edit| {
         let n_existing_items = impl_item_list.impl_items().count();
         let items = missing_items
             .into_iter()
@@ -150,9 +150,7 @@ fn add_missing_impl_members_inner(
 
         edit.replace_ast(impl_item_list, new_impl_item_list);
         edit.set_cursor(cursor_position);
-    });
-
-    ctx.build()
+    })
 }
 
 fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
diff --git a/crates/ra_assists/src/assists/apply_demorgan.rs b/crates/ra_assists/src/assists/apply_demorgan.rs
index 8d5984a583..068da1774d 100644
--- a/crates/ra_assists/src/assists/apply_demorgan.rs
+++ b/crates/ra_assists/src/assists/apply_demorgan.rs
@@ -23,7 +23,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     if !(x == 4 && y) {}
 // }
 // ```
-pub(crate) fn apply_demorgan(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn apply_demorgan(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let expr = ctx.find_node_at_offset::<ast::BinExpr>()?;
     let op = expr.op_kind()?;
     let op_range = expr.op_token()?.text_range();
@@ -39,13 +39,12 @@ pub(crate) fn apply_demorgan(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Ass
     let not_lhs = undo_negation(lhs)?;
     let not_rhs = undo_negation(rhs)?;
 
-    ctx.add_action(AssistId("apply_demorgan"), "apply demorgan's law", |edit| {
+    ctx.add_assist(AssistId("apply_demorgan"), "apply demorgan's law", |edit| {
         edit.target(op_range);
         edit.replace(op_range, opposite_op);
         edit.replace(lhs_range, format!("!({}", not_lhs));
         edit.replace(rhs_range, format!("{})", not_rhs));
-    });
-    ctx.build()
+    })
 }
 
 // Return the opposite text for a given logical operator, if it makes sense
diff --git a/crates/ra_assists/src/assists/change_visibility.rs b/crates/ra_assists/src/assists/change_visibility.rs
index 770ea04fa3..132c9dc1d7 100644
--- a/crates/ra_assists/src/assists/change_visibility.rs
+++ b/crates/ra_assists/src/assists/change_visibility.rs
@@ -29,7 +29,7 @@ pub(crate) fn change_visibility(ctx: AssistCtx<impl HirDatabase>) -> Option<Assi
     add_vis(ctx)
 }
 
-fn add_vis(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+fn add_vis(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let item_keyword = ctx.token_at_offset().find(|leaf| match leaf.kind() {
         T![fn] | T![mod] | T![struct] | T![enum] | T![trait] => true,
         _ => false,
@@ -57,13 +57,11 @@ fn add_vis(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
         (vis_offset(field.syntax()), ident.text_range())
     };
 
-    ctx.add_action(AssistId("change_visibility"), "make pub(crate)", |edit| {
+    ctx.add_assist(AssistId("change_visibility"), "make pub(crate)", |edit| {
         edit.target(target);
         edit.insert(offset, "pub(crate) ");
         edit.set_cursor(offset);
-    });
-
-    ctx.build()
+    })
 }
 
 fn vis_offset(node: &SyntaxNode) -> TextUnit {
@@ -77,24 +75,20 @@ fn vis_offset(node: &SyntaxNode) -> TextUnit {
         .unwrap_or_else(|| node.text_range().start())
 }
 
-fn change_vis(mut ctx: AssistCtx<impl HirDatabase>, vis: ast::Visibility) -> Option<Assist> {
+fn change_vis(ctx: AssistCtx<impl HirDatabase>, vis: ast::Visibility) -> Option<Assist> {
     if vis.syntax().text() == "pub" {
-        ctx.add_action(AssistId("change_visibility"), "change to pub(crate)", |edit| {
+        return ctx.add_assist(AssistId("change_visibility"), "change to pub(crate)", |edit| {
             edit.target(vis.syntax().text_range());
             edit.replace(vis.syntax().text_range(), "pub(crate)");
             edit.set_cursor(vis.syntax().text_range().start())
         });
-
-        return ctx.build();
     }
     if vis.syntax().text() == "pub(crate)" {
-        ctx.add_action(AssistId("change_visibility"), "change to pub", |edit| {
+        return ctx.add_assist(AssistId("change_visibility"), "change to pub", |edit| {
             edit.target(vis.syntax().text_range());
             edit.replace(vis.syntax().text_range(), "pub");
             edit.set_cursor(vis.syntax().text_range().start());
         });
-
-        return ctx.build();
     }
     None
 }
diff --git a/crates/ra_assists/src/assists/early_return.rs b/crates/ra_assists/src/assists/early_return.rs
index 75822dc65a..e839d831e0 100644
--- a/crates/ra_assists/src/assists/early_return.rs
+++ b/crates/ra_assists/src/assists/early_return.rs
@@ -35,7 +35,7 @@ use crate::{
 //     bar();
 // }
 // ```
-pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn convert_to_guarded_return(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
     let expr = if_expr.condition()?.expr()?;
     let then_block = if_expr.then_branch()?.block()?;
@@ -75,7 +75,7 @@ pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) ->
     then_block.syntax().last_child_or_token().filter(|t| t.kind() == R_CURLY)?;
     let cursor_position = ctx.frange.range.start();
 
-    ctx.add_action(AssistId("convert_to_guarded_return"), "convert to guarded return", |edit| {
+    ctx.add_assist(AssistId("convert_to_guarded_return"), "convert to guarded return", |edit| {
         let if_indent_level = IndentLevel::from_node(&if_expr.syntax());
         let new_if_expr =
             if_indent_level.increase_indent(make::if_expression(&expr, early_expression));
@@ -105,8 +105,7 @@ pub(crate) fn convert_to_guarded_return(mut ctx: AssistCtx<impl HirDatabase>) ->
         edit.target(if_expr.syntax().text_range());
         edit.replace_ast(parent_block, ast::Block::cast(new_block).unwrap());
         edit.set_cursor(cursor_position);
-    });
-    ctx.build()
+    })
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/fill_match_arms.rs b/crates/ra_assists/src/assists/fill_match_arms.rs
index c62c0efbef..2b74f355c6 100644
--- a/crates/ra_assists/src/assists/fill_match_arms.rs
+++ b/crates/ra_assists/src/assists/fill_match_arms.rs
@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn fill_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let match_expr = ctx.find_node_at_offset::<ast::MatchExpr>()?;
     let match_arm_list = match_expr.match_arm_list()?;
 
@@ -53,7 +53,7 @@ pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
     };
     let variant_list = enum_def.variant_list()?;
 
-    ctx.add_action(AssistId("fill_match_arms"), "fill match arms", |edit| {
+    ctx.add_assist(AssistId("fill_match_arms"), "fill match arms", |edit| {
         let indent_level = IndentLevel::from_node(match_arm_list.syntax());
 
         let new_arm_list = {
@@ -67,9 +67,7 @@ pub(crate) fn fill_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
         edit.target(match_expr.syntax().text_range());
         edit.set_cursor(expr.syntax().text_range().start());
         edit.replace_ast(match_arm_list, new_arm_list);
-    });
-
-    ctx.build()
+    })
 }
 
 fn is_trivial(arm: &ast::MatchArm) -> bool {
diff --git a/crates/ra_assists/src/assists/flip_binexpr.rs b/crates/ra_assists/src/assists/flip_binexpr.rs
index 9765d5dddc..386045eb0a 100644
--- a/crates/ra_assists/src/assists/flip_binexpr.rs
+++ b/crates/ra_assists/src/assists/flip_binexpr.rs
@@ -18,7 +18,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let _ = 2 + 90;
 // }
 // ```
-pub(crate) fn flip_binexpr(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_binexpr(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let expr = ctx.find_node_at_offset::<BinExpr>()?;
     let lhs = expr.lhs()?.syntax().clone();
     let rhs = expr.rhs()?.syntax().clone();
@@ -34,16 +34,14 @@ pub(crate) fn flip_binexpr(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assis
         return None;
     }
 
-    ctx.add_action(AssistId("flip_binexpr"), "flip binary expression", |edit| {
+    ctx.add_assist(AssistId("flip_binexpr"), "flip binary expression", |edit| {
         edit.target(op_range);
         if let FlipAction::FlipAndReplaceOp(new_op) = action {
             edit.replace(op_range, new_op);
         }
         edit.replace(lhs.text_range(), rhs.text());
         edit.replace(rhs.text_range(), lhs.text());
-    });
-
-    ctx.build()
+    })
 }
 
 enum FlipAction {
diff --git a/crates/ra_assists/src/assists/flip_comma.rs b/crates/ra_assists/src/assists/flip_comma.rs
index 53ba8011d7..9be1c1dc69 100644
--- a/crates/ra_assists/src/assists/flip_comma.rs
+++ b/crates/ra_assists/src/assists/flip_comma.rs
@@ -18,7 +18,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     ((3, 4), (1, 2));
 // }
 // ```
-pub(crate) fn flip_comma(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_comma(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let comma = ctx.find_token_at_offset(T![,])?;
     let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
     let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
@@ -29,13 +29,11 @@ pub(crate) fn flip_comma(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
         return None;
     }
 
-    ctx.add_action(AssistId("flip_comma"), "flip comma", |edit| {
+    ctx.add_assist(AssistId("flip_comma"), "flip comma", |edit| {
         edit.target(comma.text_range());
         edit.replace(prev.text_range(), next.to_string());
         edit.replace(next.text_range(), prev.to_string());
-    });
-
-    ctx.build()
+    })
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/flip_trait_bound.rs b/crates/ra_assists/src/assists/flip_trait_bound.rs
index 1625b241f1..6017b39dd8 100644
--- a/crates/ra_assists/src/assists/flip_trait_bound.rs
+++ b/crates/ra_assists/src/assists/flip_trait_bound.rs
@@ -18,7 +18,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // fn foo<T: Copy + Clone>() { }
 // ```
-pub(crate) fn flip_trait_bound(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_trait_bound(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     // We want to replicate the behavior of `flip_binexpr` by only suggesting
     // the assist when the cursor is on a `+`
     let plus = ctx.find_token_at_offset(T![+])?;
@@ -33,13 +33,11 @@ pub(crate) fn flip_trait_bound(mut ctx: AssistCtx<impl HirDatabase>) -> Option<A
         non_trivia_sibling(plus.clone().into(), Direction::Next)?,
     );
 
-    ctx.add_action(AssistId("flip_trait_bound"), "flip trait bound", |edit| {
+    ctx.add_assist(AssistId("flip_trait_bound"), "flip trait bound", |edit| {
         edit.target(plus.text_range());
         edit.replace(before.text_range(), after.to_string());
         edit.replace(after.text_range(), before.to_string());
-    });
-
-    ctx.build()
+    })
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/inline_local_variable.rs b/crates/ra_assists/src/assists/inline_local_variable.rs
index fe8fa2a868..f439105748 100644
--- a/crates/ra_assists/src/assists/inline_local_variable.rs
+++ b/crates/ra_assists/src/assists/inline_local_variable.rs
@@ -23,7 +23,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     (1 + 2) * 4;
 // }
 // ```
-pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn inline_local_varialbe(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let let_stmt = ctx.find_node_at_offset::<ast::LetStmt>()?;
     let bind_pat = match let_stmt.pat()? {
         ast::Pat::BindPat(pat) => pat,
@@ -93,7 +93,7 @@ pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Opt
     let init_str = initializer_expr.syntax().text().to_string();
     let init_in_paren = format!("({})", &init_str);
 
-    ctx.add_action(
+    ctx.add_assist(
         AssistId("inline_local_variable"),
         "inline local variable",
         move |edit: &mut AssistBuilder| {
@@ -107,9 +107,7 @@ pub(crate) fn inline_local_varialbe(mut ctx: AssistCtx<impl HirDatabase>) -> Opt
             }
             edit.set_cursor(delete_range.start())
         },
-    );
-
-    ctx.build()
+    )
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/introduce_variable.rs b/crates/ra_assists/src/assists/introduce_variable.rs
index 8245dc99f5..0623d44759 100644
--- a/crates/ra_assists/src/assists/introduce_variable.rs
+++ b/crates/ra_assists/src/assists/introduce_variable.rs
@@ -28,7 +28,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     var_name * 4;
 // }
 // ```
-pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn introduce_variable(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     if ctx.frange.range.is_empty() {
         return None;
     }
@@ -43,7 +43,7 @@ pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option
     if indent.kind() != WHITESPACE {
         return None;
     }
-    ctx.add_action(AssistId("introduce_variable"), "introduce variable", move |edit| {
+    ctx.add_assist(AssistId("introduce_variable"), "introduce variable", move |edit| {
         let mut buf = String::new();
 
         let cursor_offset = if wrap_in_block {
@@ -88,9 +88,7 @@ pub(crate) fn introduce_variable(mut ctx: AssistCtx<impl HirDatabase>) -> Option
             }
         }
         edit.set_cursor(anchor_stmt.text_range().start() + cursor_offset);
-    });
-
-    ctx.build()
+    })
 }
 
 /// Check whether the node is a valid expression which can be extracted to a variable.
diff --git a/crates/ra_assists/src/assists/merge_match_arms.rs b/crates/ra_assists/src/assists/merge_match_arms.rs
index b0c4ee78b5..e9f2cae91d 100644
--- a/crates/ra_assists/src/assists/merge_match_arms.rs
+++ b/crates/ra_assists/src/assists/merge_match_arms.rs
@@ -26,7 +26,7 @@ use ra_syntax::ast::{AstNode, MatchArm};
 //     }
 // }
 // ```
-pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn merge_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let current_arm = ctx.find_node_at_offset::<MatchArm>()?;
 
     // We check if the following match arm matches this one. We could, but don't,
@@ -52,7 +52,7 @@ pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<A
 
     let cursor_to_end = current_arm.syntax().text_range().end() - ctx.frange.range.start();
 
-    ctx.add_action(AssistId("merge_match_arms"), "merge match arms", |edit| {
+    ctx.add_assist(AssistId("merge_match_arms"), "merge match arms", |edit| {
         fn contains_placeholder(a: &MatchArm) -> bool {
             a.pats().any(|x| match x {
                 ra_syntax::ast::Pat::PlaceholderPat(..) => true,
@@ -80,9 +80,7 @@ pub(crate) fn merge_match_arms(mut ctx: AssistCtx<impl HirDatabase>) -> Option<A
         edit.target(current_arm.syntax().text_range());
         edit.replace(TextRange::from_to(start, end), arm);
         edit.set_cursor(start + offset);
-    });
-
-    ctx.build()
+    })
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/move_bounds.rs b/crates/ra_assists/src/assists/move_bounds.rs
index edf2897c6c..3145d7625d 100644
--- a/crates/ra_assists/src/assists/move_bounds.rs
+++ b/crates/ra_assists/src/assists/move_bounds.rs
@@ -22,7 +22,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     f(x)
 // }
 // ```
-pub(crate) fn move_bounds_to_where_clause(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let type_param_list = ctx.find_node_at_offset::<ast::TypeParamList>()?;
 
     let mut type_params = type_param_list.type_params();
@@ -46,38 +46,30 @@ pub(crate) fn move_bounds_to_where_clause(mut ctx: AssistCtx<impl HirDatabase>)
         _ => return None,
     };
 
-    ctx.add_action(
-        AssistId("move_bounds_to_where_clause"),
-        "move_bounds_to_where_clause",
-        |edit| {
-            let new_params = type_param_list
-                .type_params()
-                .filter(|it| it.type_bound_list().is_some())
-                .map(|type_param| {
-                    let without_bounds = type_param.remove_bounds();
-                    (type_param, without_bounds)
-                });
+    ctx.add_assist(AssistId("move_bounds_to_where_clause"), "move_bounds_to_where_clause", |edit| {
+        let new_params = type_param_list
+            .type_params()
+            .filter(|it| it.type_bound_list().is_some())
+            .map(|type_param| {
+                let without_bounds = type_param.remove_bounds();
+                (type_param, without_bounds)
+            });
 
-            let new_type_param_list = edit::replace_descendants(&type_param_list, new_params);
-            edit.replace_ast(type_param_list.clone(), new_type_param_list);
+        let new_type_param_list = edit::replace_descendants(&type_param_list, new_params);
+        edit.replace_ast(type_param_list.clone(), new_type_param_list);
 
-            let where_clause = {
-                let predicates = type_param_list.type_params().filter_map(build_predicate);
-                make::where_clause(predicates)
-            };
+        let where_clause = {
+            let predicates = type_param_list.type_params().filter_map(build_predicate);
+            make::where_clause(predicates)
+        };
 
-            let to_insert = match anchor.prev_sibling_or_token() {
-                Some(ref elem) if elem.kind() == WHITESPACE => {
-                    format!("{} ", where_clause.syntax())
-                }
-                _ => format!(" {}", where_clause.syntax()),
-            };
-            edit.insert(anchor.text_range().start(), to_insert);
-            edit.target(type_param_list.syntax().text_range());
-        },
-    );
-
-    ctx.build()
+        let to_insert = match anchor.prev_sibling_or_token() {
+            Some(ref elem) if elem.kind() == WHITESPACE => format!("{} ", where_clause.syntax()),
+            _ => format!(" {}", where_clause.syntax()),
+        };
+        edit.insert(anchor.text_range().start(), to_insert);
+        edit.target(type_param_list.syntax().text_range());
+    })
 }
 
 fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
diff --git a/crates/ra_assists/src/assists/move_guard.rs b/crates/ra_assists/src/assists/move_guard.rs
index e820a73c8d..b49ec6172a 100644
--- a/crates/ra_assists/src/assists/move_guard.rs
+++ b/crates/ra_assists/src/assists/move_guard.rs
@@ -32,7 +32,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let match_arm = ctx.find_node_at_offset::<MatchArm>()?;
     let guard = match_arm.guard()?;
     let space_before_guard = guard.syntax().prev_sibling_or_token();
@@ -41,7 +41,7 @@ pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Op
     let arm_expr = match_arm.expr()?;
     let buf = format!("if {} {{ {} }}", guard_conditions.syntax().text(), arm_expr.syntax().text());
 
-    ctx.add_action(AssistId("move_guard_to_arm_body"), "move guard to arm body", |edit| {
+    ctx.add_assist(AssistId("move_guard_to_arm_body"), "move guard to arm body", |edit| {
         edit.target(guard.syntax().text_range());
         let offseting_amount = match space_before_guard.and_then(|it| it.into_token()) {
             Some(tok) => {
@@ -61,8 +61,7 @@ pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Op
         edit.set_cursor(
             arm_expr.syntax().text_range().start() + TextUnit::from(3) - offseting_amount,
         );
-    });
-    ctx.build()
+    })
 }
 
 // Assist: move_arm_cond_to_match_guard
@@ -90,7 +89,7 @@ pub(crate) fn move_guard_to_arm_body(mut ctx: AssistCtx<impl HirDatabase>) -> Op
 //     }
 // }
 // ```
-pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
     let last_match_pat = match_arm.pats().last()?;
 
@@ -110,7 +109,7 @@ pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>)
 
     let buf = format!(" if {}", cond.syntax().text());
 
-    ctx.add_action(
+    ctx.add_assist(
         AssistId("move_arm_cond_to_match_guard"),
         "move condition to match guard",
         |edit| {
@@ -127,8 +126,7 @@ pub(crate) fn move_arm_cond_to_match_guard(mut ctx: AssistCtx<impl HirDatabase>)
             edit.insert(last_match_pat.syntax().text_range().end(), buf);
             edit.set_cursor(last_match_pat.syntax().text_range().end() + TextUnit::from(1));
         },
-    );
-    ctx.build()
+    )
 }
 
 #[cfg(test)]
diff --git a/crates/ra_assists/src/assists/raw_string.rs b/crates/ra_assists/src/assists/raw_string.rs
index 2df48a8380..86bbaeeeff 100644
--- a/crates/ra_assists/src/assists/raw_string.rs
+++ b/crates/ra_assists/src/assists/raw_string.rs
@@ -22,7 +22,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     r#"Hello, World!"#;
 // }
 // ```
-pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn make_raw_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let token = ctx.find_token_at_offset(STRING)?;
     let text = token.text().as_str();
     let usual_string_range = find_usual_string_range(text)?;
@@ -41,7 +41,7 @@ pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
     if error.is_err() {
         return None;
     }
-    ctx.add_action(AssistId("make_raw_string"), "make raw string", |edit| {
+    ctx.add_assist(AssistId("make_raw_string"), "make raw string", |edit| {
         edit.target(token.text_range());
         let max_hash_streak = count_hashes(&unescaped);
         let mut hashes = String::with_capacity(max_hash_streak + 1);
@@ -49,8 +49,7 @@ pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
             hashes.push('#');
         }
         edit.replace(token.text_range(), format!("r{}\"{}\"{}", hashes, unescaped, hashes));
-    });
-    ctx.build()
+    })
 }
 
 // Assist: make_usual_string
@@ -68,11 +67,11 @@ pub(crate) fn make_raw_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<As
 //     "Hello, \"World!\"";
 // }
 // ```
-pub(crate) fn make_usual_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn make_usual_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
     let text = token.text().as_str();
     let usual_string_range = find_usual_string_range(text)?;
-    ctx.add_action(AssistId("make_usual_string"), "make usual string", |edit| {
+    ctx.add_assist(AssistId("make_usual_string"), "make usual string", |edit| {
         edit.target(token.text_range());
         // parse inside string to escape `"`
         let start_of_inside = usual_string_range.start().to_usize() + 1;
@@ -80,8 +79,7 @@ pub(crate) fn make_usual_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<
         let inside_str = &text[start_of_inside..end_of_inside];
         let escaped = inside_str.escape_default().to_string();
         edit.replace(token.text_range(), format!("\"{}\"", escaped));
-    });
-    ctx.build()
+    })
 }
 
 // Assist: add_hash
@@ -99,14 +97,13 @@ pub(crate) fn make_usual_string(mut ctx: AssistCtx<impl HirDatabase>) -> Option<
 //     r##"Hello, World!"##;
 // }
 // ```
-pub(crate) fn add_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
-    ctx.add_action(AssistId("add_hash"), "add hash to raw string", |edit| {
+    ctx.add_assist(AssistId("add_hash"), "add hash to raw string", |edit| {
         edit.target(token.text_range());
         edit.insert(token.text_range().start() + TextUnit::of_char('r'), "#");
         edit.insert(token.text_range().end(), "#");
-    });
-    ctx.build()
+    })
 }
 
 // Assist: remove_hash
@@ -124,14 +121,14 @@ pub(crate) fn add_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
 //     r"Hello, World!";
 // }
 // ```
-pub(crate) fn remove_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn remove_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
     let text = token.text().as_str();
     if text.starts_with("r\"") {
         // no hash to remove
         return None;
     }
-    ctx.add_action(AssistId("remove_hash"), "remove hash from raw string", |edit| {
+    ctx.add_assist(AssistId("remove_hash"), "remove hash from raw string", |edit| {
         edit.target(token.text_range());
         let result = &text[2..text.len() - 1];
         let result = if result.starts_with("\"") {
@@ -142,8 +139,7 @@ pub(crate) fn remove_hash(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist
             result.to_owned()
         };
         edit.replace(token.text_range(), format!("r{}", result));
-    });
-    ctx.build()
+    })
 }
 
 fn count_hashes(s: &str) -> usize {
diff --git a/crates/ra_assists/src/assists/remove_dbg.rs b/crates/ra_assists/src/assists/remove_dbg.rs
index 44b8de8145..aedf8747f2 100644
--- a/crates/ra_assists/src/assists/remove_dbg.rs
+++ b/crates/ra_assists/src/assists/remove_dbg.rs
@@ -21,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     92;
 // }
 // ```
-pub(crate) fn remove_dbg(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn remove_dbg(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let macro_call = ctx.find_node_at_offset::<ast::MacroCall>()?;
 
     if !is_valid_macrocall(&macro_call, "dbg")? {
@@ -58,13 +58,11 @@ pub(crate) fn remove_dbg(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
         text.slice(without_parens).to_string()
     };
 
-    ctx.add_action(AssistId("remove_dbg"), "remove dbg!()", |edit| {
+    ctx.add_assist(AssistId("remove_dbg"), "remove dbg!()", |edit| {
         edit.target(macro_call.syntax().text_range());
         edit.replace(macro_range, macro_content);
         edit.set_cursor(cursor_pos);
-    });
-
-    ctx.build()
+    })
 }
 
 /// Verifies that the given macro_call actually matches the given name
diff --git a/crates/ra_assists/src/assists/replace_if_let_with_match.rs b/crates/ra_assists/src/assists/replace_if_let_with_match.rs
index 58ef2ff206..dff84d8651 100644
--- a/crates/ra_assists/src/assists/replace_if_let_with_match.rs
+++ b/crates/ra_assists/src/assists/replace_if_let_with_match.rs
@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn replace_if_let_with_match(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn replace_if_let_with_match(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
     let cond = if_expr.condition()?;
     let pat = cond.pat()?;
@@ -42,14 +42,12 @@ pub(crate) fn replace_if_let_with_match(mut ctx: AssistCtx<impl HirDatabase>) ->
         ast::ElseBranch::IfExpr(_) => return None,
     };
 
-    ctx.add_action(AssistId("replace_if_let_with_match"), "replace with match", |edit| {
+    ctx.add_assist(AssistId("replace_if_let_with_match"), "replace with match", |edit| {
         let match_expr = build_match_expr(expr, pat, then_block, else_block);
         edit.target(if_expr.syntax().text_range());
         edit.replace_node_and_indent(if_expr.syntax(), match_expr);
         edit.set_cursor(if_expr.syntax().text_range().start())
-    });
-
-    ctx.build()
+    })
 }
 
 fn build_match_expr(
diff --git a/crates/ra_assists/src/assists/split_import.rs b/crates/ra_assists/src/assists/split_import.rs
index 8d8a289878..5f8d6b0be1 100644
--- a/crates/ra_assists/src/assists/split_import.rs
+++ b/crates/ra_assists/src/assists/split_import.rs
@@ -16,7 +16,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // use std::{collections::HashMap};
 // ```
-pub(crate) fn split_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn split_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let colon_colon = ctx.find_token_at_offset(T![::])?;
     let path = ast::Path::cast(colon_colon.parent())?;
     let top_path = successors(Some(path), |it| it.parent_path()).last()?;
@@ -32,14 +32,12 @@ pub(crate) fn split_import(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assis
         None => top_path.syntax().text_range().end(),
     };
 
-    ctx.add_action(AssistId("split_import"), "split import", |edit| {
+    ctx.add_assist(AssistId("split_import"), "split import", |edit| {
         edit.target(colon_colon.text_range());
         edit.insert(l_curly, "{");
         edit.insert(r_curly, "}");
         edit.set_cursor(l_curly + TextUnit::of_str("{"));
-    });
-
-    ctx.build()
+    })
 }
 
 #[cfg(test)]