11 files changed, 419 insertions, 114 deletions

diff --git a/crates/ra_assists/src/assists/add_derive.rs b/crates/ra_assists/src/assists/add_derive.rs
index 77ecc33c9..d3ba634c4 100644
--- a/crates/ra_assists/src/assists/add_derive.rs
+++ b/crates/ra_assists/src/assists/add_derive.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, AstNode, AttrsOwner},
@@ -9,6 +7,22 @@ use ra_syntax::{
 
 use crate::{Assist, AssistCtx, AssistId};
 
+// Assist: add_derive
+// Adds a new `#[derive()]` clause to a struct or enum.
+// ```
+// struct Point {
+//     x: u32,
+//     y: u32,<|>
+// }
+// ```
+// ->
+// ```
+// #[derive()]
+// struct Point {
+//     x: u32,
+//     y: u32,
+// }
+// ```
 pub(crate) fn add_derive(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
     let node_start = derive_insertion_offset(&nominal)?;
diff --git a/crates/ra_assists/src/assists/add_explicit_type.rs b/crates/ra_assists/src/assists/add_explicit_type.rs
index 8c83dc987..33b7bea7f 100644
--- a/crates/ra_assists/src/assists/add_explicit_type.rs
+++ b/crates/ra_assists/src/assists/add_explicit_type.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::{db::HirDatabase, HirDisplay, Ty};
 use ra_syntax::{
     ast::{self, AstNode, LetStmt, NameOwner},
@@ -8,7 +6,19 @@ use ra_syntax::{
 
 use crate::{Assist, AssistCtx, AssistId};
 
-/// Add explicit type assist.
+// Assist: add_explicit_type
+// Specify type for a let binding
+// ```
+// fn main() {
+//     let x<|> = 92;
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let x: i32 = 92;
+// }
+// ```
 pub(crate) fn add_explicit_type(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let stmt = ctx.node_at_offset::<LetStmt>()?;
     let expr = stmt.initializer()?;
diff --git a/crates/ra_assists/src/assists/add_impl.rs b/crates/ra_assists/src/assists/add_impl.rs
index 94801fbc9..40bc5c464 100644
--- a/crates/ra_assists/src/assists/add_impl.rs
+++ b/crates/ra_assists/src/assists/add_impl.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use format_buf::format;
 use hir::db::HirDatabase;
 use join_to_string::join;
@@ -10,6 +8,23 @@ use ra_syntax::{
 
 use crate::{Assist, AssistCtx, AssistId};
 
+// Assist: add_impl
+// Adds a new inherent impl for a type
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,<|>
+// }
+// ```
+// ->
+// ```
+// struct Ctx<T: Clone> {
+//      data: T,
+// }
+//
+// impl<T: Clone> Ctx<T> {
+//
+// }
+// ```
 pub(crate) fn add_impl(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
     let name = nominal.name()?;
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 565b96fb5..36fa6f9ea 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -1,5 +1,3 @@
-//! FIXME: write short doc here
-
 use hir::{db::HirDatabase, HasSource};
 use ra_syntax::{
     ast::{self, edit, make, AstNode, NameOwner},
@@ -14,6 +12,32 @@ enum AddMissingImplMembersMode {
     NoDefaultMethods,
 }
 
+// Assist: add_impl_missing_members
+// Adds scaffold for required impl members
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     fn foo(&self) { unimplemented!() }
+//
+// }
+// ```
 pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     add_missing_impl_members_inner(
         ctx,
@@ -23,6 +47,36 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Opti
     )
 }
 
+// Assist: add_impl_default_members
+// Adds scaffold for overriding default impl members
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     Type X = ();
+//     fn foo(&self) {}<|>
+//
+// }
+// ```
+// ->
+// ```
+// trait T {
+//     Type X;
+//     fn foo(&self);
+//     fn bar(&self) {}
+// }
+//
+// impl T for () {
+//     Type X = ();
+//     fn foo(&self) {}
+//     fn bar(&self) {}
+//
+// }
+// ```
 pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     add_missing_impl_members_inner(
         ctx,
diff --git a/crates/ra_assists/src/assists/apply_demorgan.rs b/crates/ra_assists/src/assists/apply_demorgan.rs
index 5f2b0dd18..a072f63e7 100644
--- a/crates/ra_assists/src/assists/apply_demorgan.rs
+++ b/crates/ra_assists/src/assists/apply_demorgan.rs
@@ -1,18 +1,26 @@
-//! This contains the functions associated with the demorgan assist.
-//! This assist transforms boolean expressions of the form `!a || !b` into
-//! `!(a && b)`.
 use hir::db::HirDatabase;
 use ra_syntax::ast::{self, AstNode};
 use ra_syntax::SyntaxNode;
 
 use crate::{Assist, AssistCtx, AssistId};
 
-/// Assist for applying demorgan's law
-///
-/// This transforms expressions of the form `!l || !r` into `!(l && r)`.
-/// This also works with `&&`. This assist can only be applied with the cursor
-/// on either `||` or `&&`, with both operands being a negation of some kind.
-/// This means something of the form `!x` or `x != y`.
+// Assist: apply_demorgan
+// Apply [De Morgan's law](https://en.wikipedia.org/wiki/De_Morgan%27s_laws).
+// This transforms expressions of the form `!l || !r` into `!(l && r)`.
+// This also works with `&&`. This assist can only be applied with the cursor
+// on either `||` or `&&`, with both operands being a negation of some kind.
+// This means something of the form `!x` or `x != y`.
+// ```
+// fn main() {
+//     if x != 4 ||<|> !y {}
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if !(x == 4 && y) {}
+// }
+// ```
 pub(crate) fn apply_demorgan(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let expr = ctx.node_at_offset::<ast::BinExpr>()?;
     let op = expr.op_kind()?;
diff --git a/crates/ra_assists/src/doc_tests.rs b/crates/ra_assists/src/doc_tests.rs
index 88e901517..872bbdf17 100644
--- a/crates/ra_assists/src/doc_tests.rs
+++ b/crates/ra_assists/src/doc_tests.rs
@@ -15,8 +15,10 @@ fn check(assist_id: &str, before: &str, after: &str) {
     let (db, _source_root, file_id) = MockDatabase::with_single_file(&before);
     let frange = FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
 
-    let (_assist_id, action) =
-        crate::assists(&db, frange).into_iter().find(|(id, _)| id.id.0 == assist_id).unwrap();
+    let (_assist_id, action) = crate::assists(&db, frange)
+        .into_iter()
+        .find(|(id, _)| id.id.0 == assist_id)
+        .unwrap_or_else(|| panic!("Assist {:?} is not applicable", assist_id));
 
     let actual = action.edit.apply(&before);
     assert_eq_text!(after, &actual);
diff --git a/crates/ra_assists/src/doc_tests/generated.rs b/crates/ra_assists/src/doc_tests/generated.rs
index e5f6910f1..76d86b93d 100644
--- a/crates/ra_assists/src/doc_tests/generated.rs
+++ b/crates/ra_assists/src/doc_tests/generated.rs
@@ -3,6 +3,145 @@
 use super::check;
 
 #[test]
+fn doctest_add_derive() {
+    check(
+        "add_derive",
+        r#####"
+struct Point {
+    x: u32,
+    y: u32,<|>
+}
+"#####,
+        r#####"
+#[derive()]
+struct Point {
+    x: u32,
+    y: u32,
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_explicit_type() {
+    check(
+        "add_explicit_type",
+        r#####"
+fn main() {
+    let x<|> = 92;
+}
+"#####,
+        r#####"
+fn main() {
+    let x: i32 = 92;
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_impl() {
+    check(
+        "add_impl",
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,<|>
+}
+"#####,
+        r#####"
+struct Ctx<T: Clone> {
+     data: T,
+}
+
+impl<T: Clone> Ctx<T> {
+
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_impl_default_members() {
+    check(
+        "add_impl_default_members",
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}<|>
+
+}
+"#####,
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}
+    fn bar(&self) {}
+
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_add_impl_missing_members() {
+    check(
+        "add_impl_missing_members",
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {<|>
+
+}
+"#####,
+        r#####"
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    fn foo(&self) { unimplemented!() }
+
+}
+"#####,
+    )
+}
+
+#[test]
+fn doctest_apply_demorgan() {
+    check(
+        "apply_demorgan",
+        r#####"
+fn main() {
+    if x != 4 ||<|> !y {}
+}
+"#####,
+        r#####"
+fn main() {
+    if !(x == 4 && y) {}
+}
+"#####,
+    )
+}
+
+#[test]
 fn doctest_convert_to_guarded_return() {
     check(
         "convert_to_guarded_return",
diff --git a/docs/user/assists.md b/docs/user/assists.md
index cb4b0b9fb..eeb486832 100644
--- a/docs/user/assists.md
+++ b/docs/user/assists.md
@@ -1,5 +1,142 @@
 # Assists
 
+## `add_derive`
+
+Adds a new `#[derive()]` clause to a struct or enum.
+
+```rust
+// BEFORE
+struct Point {
+    x: u32,
+    y: u32,<|>
+}
+
+// AFTER
+#[derive()]
+struct Point {
+    x: u32,
+    y: u32,
+}
+```
+
+## `add_explicit_type`
+
+Specify type for a let binding
+
+```rust
+// BEFORE
+fn main() {
+    let x<|> = 92;
+}
+
+// AFTER
+fn main() {
+    let x: i32 = 92;
+}
+```
+
+## `add_impl`
+
+Adds a new inherent impl for a type
+
+```rust
+// BEFORE
+struct Ctx<T: Clone> {
+     data: T,<|>
+}
+
+// AFTER
+struct Ctx<T: Clone> {
+     data: T,
+}
+
+impl<T: Clone> Ctx<T> {
+
+}
+```
+
+## `add_impl_default_members`
+
+Adds scaffold for overriding default impl members
+
+```rust
+// BEFORE
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}<|>
+
+}
+
+// AFTER
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    Type X = ();
+    fn foo(&self) {}
+    fn bar(&self) {}
+
+}
+```
+
+## `add_impl_missing_members`
+
+Adds scaffold for required impl members
+
+```rust
+// BEFORE
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {<|>
+
+}
+
+// AFTER
+trait T {
+    Type X;
+    fn foo(&self);
+    fn bar(&self) {}
+}
+
+impl T for () {
+    fn foo(&self) { unimplemented!() }
+
+}
+```
+
+## `apply_demorgan`
+
+Apply [De Morgan's law](https://en.wikipedia.org/wiki/De_Morgan%27s_laws).
+This transforms expressions of the form `!l || !r` into `!(l && r)`.
+This also works with `&&`. This assist can only be applied with the cursor
+on either `||` or `&&`, with both operands being a negation of some kind.
+This means something of the form `!x` or `x != y`.
+
+```rust
+// BEFORE
+fn main() {
+    if x != 4 ||<|> !y {}
+}
+
+// AFTER
+fn main() {
+    if !(x == 4 && y) {}
+}
+```
+
 ## `convert_to_guarded_return`
 
 Replace a large conditional with a guarded return.
diff --git a/docs/user/features.md b/docs/user/features.md
index a94b65ad4..acf092cec 100644
--- a/docs/user/features.md
+++ b/docs/user/features.md
@@ -104,84 +104,6 @@ the VS Code side to be able to position cursor. `<|>` signifies cursor
 
 See [assists.md](./assists.md)
 
-- Add `#[derive]`
-
-```rust
-// before:
-struct Foo {
-    <|>x: i32
-}
-// after:
-#[derive(<|>)]
-struct Foo {
-    x: i32
-}
-```
-
-- Add `impl`
-
-```rust
-// before:
-struct Foo<'a, T: Debug> {
-    <|>t: T
-}
-// after:
-struct Foo<'a, T: Debug> {
-    t: T
-}
-
-impl<'a, T: Debug> Foo<'a, T> {
-    <|>
-}
-```
-
-- Add missing `impl` members
-
-```rust
-// before:
-trait Foo {
-    fn foo(&self);
-    fn bar(&self);
-    fn baz(&self);
-}
-
-struct S;
-
-impl Foo for S {
-    fn bar(&self) {}
-    <|>
-}
-
-// after:
-trait Foo {
-    fn foo(&self);
-    fn bar(&self);
-    fn baz(&self);
-}
-
-struct S;
-
-impl Foo for S {
-    fn bar(&self) {}
-    fn foo(&self) { unimplemented!() }
-    fn baz(&self) { unimplemented!() }<|>
-}
-```
-
-- Apply [De Morgan's law](https://en.wikipedia.org/wiki/De_Morgan%27s_laws)
-
-```rust
-// before:
-fn example(x: bool) -> bool {
-    !x || !x
-}
-
-// after:
-fn example(x: bool) -> bool {
-    !(x && x)
-}
-```
-
 - Import path
 
 ```rust
@@ -391,19 +313,6 @@ fn foo() {
 }
 ```
 
-- Add explicit type
-
-```rust
-// before:
-fn foo() {
-    let t<|> = (&2, Some(1));
-}
-// after:
-fn foo() {
-    let t<|>: (&i32, Option<i32>) = (&2, Some(1));
-}
-```
-
 - Move guard expression to match arm body
 ```rust
 // before:
diff --git a/xtask/src/codegen.rs b/xtask/src/codegen.rs
index 44729cd57..4ec8ab75a 100644
--- a/xtask/src/codegen.rs
+++ b/xtask/src/codegen.rs
@@ -74,6 +74,14 @@ fn reformat(text: impl std::fmt::Display) -> Result<String> {
 }
 
 fn extract_comment_blocks(text: &str) -> Vec<Vec<String>> {
+    do_extract_comment_blocks(text, false)
+}
+
+fn extract_comment_blocks_with_empty_lines(text: &str) -> Vec<Vec<String>> {
+    do_extract_comment_blocks(text, true)
+}
+
+fn do_extract_comment_blocks(text: &str, allow_blocks_with_empty_lins: bool) -> Vec<Vec<String>> {
     let mut res = Vec::new();
 
     let prefix = "// ";
@@ -81,6 +89,11 @@ fn extract_comment_blocks(text: &str) -> Vec<Vec<String>> {
 
     let mut block = vec![];
     for line in lines {
+        if line == "//" && allow_blocks_with_empty_lins {
+            block.push(String::new());
+            continue;
+        }
+
         let is_comment = line.starts_with(prefix);
         if is_comment {
             block.push(line[prefix.len()..].to_string());
diff --git a/xtask/src/codegen/gen_assists_docs.rs b/xtask/src/codegen/gen_assists_docs.rs
index 654ae09d6..e313820d1 100644
--- a/xtask/src/codegen/gen_assists_docs.rs
+++ b/xtask/src/codegen/gen_assists_docs.rs
@@ -1,7 +1,7 @@
 use std::{fs, path::Path};
 
 use crate::{
-    codegen::{self, extract_comment_blocks, Mode},
+    codegen::{self, extract_comment_blocks_with_empty_lines, Mode},
     project_root, Result,
 };
 
@@ -34,7 +34,7 @@ fn collect_assists() -> Result<Vec<Assist>> {
 
     fn collect_file(acc: &mut Vec<Assist>, path: &Path) -> Result<()> {
         let text = fs::read_to_string(path)?;
-        let comment_blocks = extract_comment_blocks(&text);
+        let comment_blocks = extract_comment_blocks_with_empty_lines(&text);
 
         for block in comment_blocks {
             // FIXME: doesn't support blank lines yet, need to tweak
@@ -45,7 +45,11 @@ fn collect_assists() -> Result<Vec<Assist>> {
                 continue;
             }
             let id = first_line["Assist: ".len()..].to_string();
-            assert!(id.chars().all(|it| it.is_ascii_lowercase() || it == '_'));
+            assert!(
+                id.chars().all(|it| it.is_ascii_lowercase() || it == '_'),
+                "invalid assist id: {:?}",
+                id
+            );
 
             let doc = take_until(lines.by_ref(), "```");
             let before = take_until(lines.by_ref(), "```");