Repository: rust-lang/rust-analyzer (rust)

Issue:
New Assist: From/To cfg_attr
Wrapping an attribute into `#[cfg_attr` isn't a lot of work, but can be tedious nonetheless.

I propose an assist that will convert
```
#[some_attr(...)]    ->  #[cfg_attr(todo, some_attr(...))]
#[some_attr = ...]   ->  #[cfg_attr(todo, some_attr = ...)]
#[some_attr]         ->  #[cfg_attr(todo, some_attr)]
```

and back
```
#[cfg_attr(not(all(...)), some_attr(...))]   ->  #[some_attr(...)] 
#[cfg_attr(not(all(...)), some_attr = ...)]  ->  #[some_attr = ...]
#[cfg_attr(not(all(...)), some_attr)]        ->  #[some_attr]
```

Obviously, the back direction is lossy.

This would play quite well with e.g. #13935 allowing to convert a doc comment in two steps to a conditional doc attribute.


As I'm quite new to rust-analyzer I'm not sure if this would need to somehow understand weather `cfg_attr` is actually `cfg_attr` or some custom attribute macro, which could complicate things. But other than that, this should be pretty simple to implement.

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Pull request:
Wrap/Unwrap cfg_attr
https://github.com/rust-lang/rust-analyzer/assets/11785959/f5f1bb71-22e7-438b-9a22-65ebab1b362d


https://github.com/rust-lang/rust-analyzer/assets/11785959/36933a4e-0000-455a-abe3-af774cd854d0

## TODO
- [x] Add Tests
- [x] Wrap derive elements

Closes #13965 

Patch:
diff --git a/crates/ide-assists/src/handlers/wrap_unwrap_cfg_attr.rs b/crates/ide-assists/src/handlers/wrap_unwrap_cfg_attr.rs
new file mode 100644
index 0000000000..0fa46ef43a
--- /dev/null
+++ b/crates/ide-assists/src/handlers/wrap_unwrap_cfg_attr.rs
@@ -0,0 +1,581 @@
+use ide_db::source_change::SourceChangeBuilder;
+use itertools::Itertools;
+use syntax::{
+    algo,
+    ast::{self, make, AstNode},
+    ted::{self, Position},
+    NodeOrToken, SyntaxToken, TextRange, T,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: wrap_unwrap_cfg_attr
+//
+// Wraps an attribute to a cfg_attr attribute or unwraps a cfg_attr attribute to the inner attributes.
+//
+// ```
+// #[derive$0(Debug)]
+// struct S {
+//    field: i32
+// }
+// ```
+// ->
+// ```
+// #[cfg_attr($0, derive(Debug))]
+// struct S {
+//    field: i32
+// }
+
+enum WrapUnwrapOption {
+    WrapDerive { derive: TextRange, attr: ast::Attr },
+    WrapAttr(ast::Attr),
+}
+
+/// Attempts to get the derive attribute from a derive attribute list
+///
+/// This will collect all the tokens in the "path" within the derive attribute list
+/// But a derive attribute list doesn't have paths. So we need to collect all the tokens before and after the ident
+///
+/// If this functions return None just map to WrapAttr
+fn attempt_get_derive(attr: ast::Attr, ident: SyntaxToken) -> WrapUnwrapOption {
+    let attempt_attr = || {
+        {
+            let mut derive = ident.text_range();
+            // TokenTree is all the tokens between the `(` and `)`. They do not have paths. So a path `serde::Serialize` would be [Ident Colon Colon Ident]
+            // So lets say we have derive(Debug, serde::Serialize, Copy) ident would be on Serialize
+            // We need to grab all previous tokens until we find a `,` or `(` and all following tokens until we find a `,` or `)`
+            // We also want to consume the following comma if it exists
+
+            let mut prev = algo::skip_trivia_token(
+                ident.prev_sibling_or_token()?.into_token()?,
+                syntax::Direction::Prev,
+            )?;
+            let mut following = algo::skip_trivia_token(
+                ident.next_sibling_or_token()?.into_token()?,
+                syntax::Direction::Next,
+            )?;
+            if (prev.kind() == T![,] || prev.kind() == T!['('])
+                && (following.kind() == T![,] || following.kind() == T![')'])
+            {
+                // This would be a single ident such as Debug. As no path is present
+                if following.kind() == T![,] {
+                    derive = derive.cover(following.text_range());
+                } else if following.kind() == T![')'] && prev.kind() == T![,] {
+                    derive = derive.cover(prev.text_range());
+                }
+
+                Some(WrapUnwrapOption::WrapDerive { derive, attr: attr.clone() })
+            } else {
+                let mut consumed_comma = false;
+                // Collect the path
+                while let Some(prev_token) = algo::skip_trivia_token(prev, syntax::Direction::Prev)
+                {
+                    let kind = prev_token.kind();
+                    if kind == T![,] {
+                        consumed_comma = true;
+                        derive = derive.cover(prev_token.text_range());
+                        break;
+                    } else if kind == T!['('] {
+                        break;
+                    } else {
+                        derive = derive.cover(prev_token.text_range());
+                    }
+                    prev = prev_token.prev_sibling_or_token()?.into_token()?;
+                }
+                while let Some(next_token) =
+                    algo::skip_trivia_token(following.clone(), syntax::Direction::Next)
+                {
+                    let kind = next_token.kind();
+                    match kind {
+                        T![,] if !consumed_comma => {
+                            derive = derive.cover(next_token.text_range());
+                            break;
+                        }
+                        T![')'] | T![,] => break,
+                        _ => derive = derive.cover(next_token.text_range()),
+                    }
+                    following = next_token.next_sibling_or_token()?.into_token()?;
+                }
+                Some(WrapUnwrapOption::WrapDerive { derive, attr: attr.clone() })
+            }
+        }
+    };
+    if ident.parent().and_then(ast::TokenTree::cast).is_none()
+        || !attr.simple_name().map(|v| v.eq("derive")).unwrap_or_default()
+    {
+        WrapUnwrapOption::WrapAttr(attr)
+    } else {
+        attempt_attr().unwrap_or(WrapUnwrapOption::WrapAttr(attr))
+    }
+}
+pub(crate) fn wrap_unwrap_cfg_attr(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let option = if ctx.has_empty_selection() {
+        let ident = ctx.find_token_syntax_at_offset(T![ident]);
+        let attr = ctx.find_node_at_offset::<ast::Attr>();
+        match (attr, ident) {
+            (Some(attr), Some(ident))
+                if attr.simple_name().map(|v| v.eq("derive")).unwrap_or_default() =>
+            {
+                Some(attempt_get_derive(attr.clone(), ident))
+            }
+
+            (Some(attr), _) => Some(WrapUnwrapOption::WrapAttr(attr)),
+            _ => None,
+        }
+    } else {
+        let covering_element = ctx.covering_element();
+        match covering_element {
+            NodeOrToken::Node(node) => ast::Attr::cast(node).map(WrapUnwrapOption::WrapAttr),
+            NodeOrToken::Token(ident) if ident.kind() == syntax::T![ident] => {
+                let attr = ident.parent_ancestors().find_map(ast::Attr::cast)?;
+                Some(attempt_get_derive(attr.clone(), ident))
+            }
+            _ => None,
+        }
+    }?;
+    match option {
+        WrapUnwrapOption::WrapAttr(attr) if attr.simple_name().as_deref() == Some("cfg_attr") => {
+            unwrap_cfg_attr(acc, attr)
+        }
+        WrapUnwrapOption::WrapAttr(attr) => wrap_cfg_attr(acc, ctx, attr),
+        WrapUnwrapOption::WrapDerive { derive, attr } => wrap_derive(acc, ctx, attr, derive),
+    }
+}
+
+fn wrap_derive(
+    acc: &mut Assists,
+    ctx: &AssistContext<'_>,
+    attr: ast::Attr,
+    derive_element: TextRange,
+) -> Option<()> {
+    let range = attr.syntax().text_range();
+    let token_tree = attr.token_tree()?;
+    let mut path_text = String::new();
+
+    let mut cfg_derive_tokens = Vec::new();
+    let mut new_derive = Vec::new();
+
+    for tt in token_tree.token_trees_and_tokens() {
+        let NodeOrToken::Token(token) = tt else {
+            continue;
+        };
+        if token.kind() == T!['('] || token.kind() == T![')'] {
+            continue;
+        }
+
+        if derive_element.contains_range(token.text_range()) {
+            if token.kind() != T![,] && token.kind() != syntax::SyntaxKind::WHITESPACE {
+                path_text.push_str(token.text());
+                cfg_derive_tokens.push(NodeOrToken::Token(token));
+            }
+        } else {
+            new_derive.push(NodeOrToken::Token(token));
+        }
+    }
+    let handle_source_change = |edit: &mut SourceChangeBuilder| {
+        let new_derive = make::attr_outer(make::meta_token_tree(
+            make::ext::ident_path("derive"),
+            make::token_tree(T!['('], new_derive),
+        ))
+        .clone_for_update();
+        let meta = make::meta_token_tree(
+            make::ext::ident_path("cfg_attr"),
+            make::token_tree(
+                T!['('],
+                vec![
+                    NodeOrToken::Token(make::token(T![,])),
+                    NodeOrToken::Token(make::tokens::whitespace(" ")),
+                    NodeOrToken::Token(make::tokens::ident("derive")),
+                    NodeOrToken::Node(make::token_tree(T!['('], cfg_derive_tokens)),
+                ],
+            ),
+        );
+        // Remove the derive attribute
+        let edit_attr = edit.make_syntax_mut(attr.syntax().clone());
+
+        ted::replace(edit_attr, new_derive.syntax().clone());
+        let cfg_attr = make::attr_outer(meta).clone_for_update();
+
+        ted::insert_all_raw(
+            Position::after(new_derive.syntax().clone()),
+            vec![make::tokens::whitespace("\n").into(), cfg_attr.syntax().clone().into()],
+        );
+        if let Some(snippet_cap) = ctx.config.snippet_cap {
+            if let Some(first_meta) =
+                cfg_attr.meta().and_then(|meta| meta.token_tree()).and_then(|tt| tt.l_paren_token())
+            {
+                edit.add_tabstop_after_token(snippet_cap, first_meta)
+            }
+        }
+    };
+
+    acc.add(
+        AssistId("wrap_unwrap_cfg_attr", AssistKind::Refactor),
+        format!("Wrap #[derive({path_text})] in `cfg_attr`",),
+        range,
+        handle_source_change,
+    );
+    Some(())
+}
+fn wrap_cfg_attr(acc: &mut Assists, ctx: &AssistContext<'_>, attr: ast::Attr) -> Option<()> {
+    let range = attr.syntax().text_range();
+    let path = attr.path()?;
+    let handle_source_change = |edit: &mut SourceChangeBuilder| {
+        let mut raw_tokens = vec![
+            NodeOrToken::Token(make::token(T![,])),
+            NodeOrToken::Token(make::tokens::whitespace(" ")),
+        ];
+        path.syntax().descendants_with_tokens().for_each(|it| {
+            if let NodeOrToken::Token(token) = it {
+                raw_tokens.push(NodeOrToken::Token(token));
+            }
+        });
+        if let Some(meta) = attr.meta() {
+            if let (Some(eq), Some(expr)) = (meta.eq_token(), meta.expr()) {
+                raw_tokens.push(NodeOrToken::Token(make::tokens::whitespace(" ")));
+                raw_tokens.push(NodeOrToken::Token(eq.clone()));
+                raw_tokens.push(NodeOrToken::Token(make::tokens::whitespace(" ")));
+
+                expr.syntax().descendants_with_tokens().for_each(|it| {
+                    if let NodeOrToken::Token(token) = it {
+                        raw_tokens.push(NodeOrToken::Token(token));
+                    }
+                });
+            } else if let Some(tt) = meta.token_tree() {
+                raw_tokens.extend(tt.token_trees_and_tokens());
+            }
+        }
+        let meta = make::meta_token_tree(
+            make::ext::ident_path("cfg_attr"),
+            make::token_tree(T!['('], raw_tokens),
+        );
+        let cfg_attr = if attr.excl_token().is_some() {
+            make::attr_inner(meta)
+        } else {
+            make::attr_outer(meta)
+        }
+        .clone_for_update();
+        let attr_syntax = edit.make_syntax_mut(attr.syntax().clone());
+        ted::replace(attr_syntax, cfg_attr.syntax());
+
+        if let Some(snippet_cap) = ctx.config.snippet_cap {
+            if let Some(first_meta) =
+                cfg_attr.meta().and_then(|meta| meta.token_tree()).and_then(|tt| tt.l_paren_token())
+            {
+                edit.add_tabstop_after_token(snippet_cap, first_meta)
+            }
+        }
+    };
+    acc.add(
+        AssistId("wrap_unwrap_cfg_attr", AssistKind::Refactor),
+        "Convert to `cfg_attr`",
+        range,
+        handle_source_change,
+    );
+    Some(())
+}
+fn unwrap_cfg_attr(acc: &mut Assists, attr: ast::Attr) -> Option<()> {
+    let range = attr.syntax().text_range();
+    let meta = attr.meta()?;
+    let meta_tt = meta.token_tree()?;
+    let mut inner_attrs = Vec::with_capacity(1);
+    let mut found_comma = false;
+    let mut iter = meta_tt.token_trees_and_tokens().skip(1).peekable();
+    while let Some(tt) = iter.next() {
+        if let NodeOrToken::Token(token) = &tt {
+            if token.kind() == T![')'] {
+                break;
+            }
+            if token.kind() == T![,] {
+                found_comma = true;
+                continue;
+            }
+        }
+        if !found_comma {
+            continue;
+        }
+        let Some(attr_name) = tt.into_token().and_then(|token| {
+            if token.kind() == T![ident] {
+                Some(make::ext::ident_path(token.text()))
+            } else {
+                None
+            }
+        }) else {
+            continue;
+        };
+        let next_tt = iter.next()?;
+        let meta = match next_tt {
+            NodeOrToken::Node(tt) => make::meta_token_tree(attr_name, tt),
+            NodeOrToken::Token(token) if token.kind() == T![,] || token.kind() == T![')'] => {
+                make::meta_path(attr_name)
+            }
+            NodeOrToken::Token(token) => {
+                let equals = algo::skip_trivia_token(token, syntax::Direction::Next)?;
+                if equals.kind() != T![=] {
+                    return None;
+                }
+                let expr_token =
+                    algo::skip_trivia_token(equals.next_token()?, syntax::Direction::Next)
+                        .and_then(|it| {
+                            if it.kind().is_literal() {
+                                Some(make::expr_literal(it.text()))
+                            } else {
+                                None
+                            }
+                        })?;
+                make::meta_expr(attr_name, ast::Expr::Literal(expr_token))
+            }
+        };
+        if attr.excl_token().is_some() {
+            inner_attrs.push(make::attr_inner(meta));
+        } else {
+            inner_attrs.push(make::attr_outer(meta));
+        }
+    }
+    if inner_attrs.is_empty() {
+        return None;
+    }
+    let handle_source_change = |f: &mut SourceChangeBuilder| {
+        let inner_attrs = inner_attrs.iter().map(|it| it.to_string()).join("\n");
+        f.replace(range, inner_attrs);
+    };
+    acc.add(
+        AssistId("wrap_unwrap_cfg_attr", AssistKind::Refactor),
+        "Extract Inner Attributes from `cfg_attr`",
+        range,
+        handle_source_change,
+    );
+    Some(())
+}
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_assist;
+
+    use super::*;
+
+    #[test]
+    fn test_basic_to_from_cfg_attr() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive$0(Debug)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[cfg_attr($0, derive(Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[cfg_attr(debug_assertions, $0 derive(Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive(Debug)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+    }
+    #[test]
+    fn to_from_path_attr() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            pub struct Test {
+                #[foo$0]
+                test: u32,
+            }
+            "#,
+            r#"
+            pub struct Test {
+                #[cfg_attr($0, foo)]
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            pub struct Test {
+                #[cfg_attr(debug_assertions$0, foo)]
+                test: u32,
+            }
+            "#,
+            r#"
+            pub struct Test {
+                #[foo]
+                test: u32,
+            }
+            "#,
+        );
+    }
+    #[test]
+    fn to_from_eq_attr() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            pub struct Test {
+                #[foo = "bar"$0]
+                test: u32,
+            }
+            "#,
+            r#"
+            pub struct Test {
+                #[cfg_attr($0, foo = "bar")]
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            pub struct Test {
+                #[cfg_attr(debug_assertions$0, foo = "bar")]
+                test: u32,
+            }
+            "#,
+            r#"
+            pub struct Test {
+                #[foo = "bar"]
+                test: u32,
+            }
+            "#,
+        );
+    }
+    #[test]
+    fn inner_attrs() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #![no_std$0]
+            "#,
+            r#"
+            #![cfg_attr($0, no_std)]
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #![cfg_attr(not(feature = "std")$0, no_std)]
+            "#,
+            r#"
+            #![no_std]
+            "#,
+        );
+    }
+    #[test]
+    fn test_derive_wrap() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(Debug$0, Clone, Copy)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive( Clone, Copy)]
+            #[cfg_attr($0, derive(Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(Clone, Debug$0, Copy)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive(Clone,  Copy)]
+            #[cfg_attr($0, derive(Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+    }
+    #[test]
+    fn test_derive_wrap_with_path() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(std::fmt::Debug$0, Clone, Copy)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive( Clone, Copy)]
+            #[cfg_attr($0, derive(std::fmt::Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(Clone, std::fmt::Debug$0, Copy)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive(Clone, Copy)]
+            #[cfg_attr($0, derive(std::fmt::Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+    }
+    #[test]
+    fn test_derive_wrap_at_end() {
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(std::fmt::Debug, Clone, Cop$0y)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive(std::fmt::Debug, Clone)]
+            #[cfg_attr($0, derive(Copy))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+        check_assist(
+            wrap_unwrap_cfg_attr,
+            r#"
+            #[derive(Clone, Copy, std::fmt::D$0ebug)]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+            r#"
+            #[derive(Clone, Copy)]
+            #[cfg_attr($0, derive(std::fmt::Debug))]
+            pub struct Test {
+                test: u32,
+            }
+            "#,
+        );
+    }
+}
diff --git a/crates/ide-assists/src/lib.rs b/crates/ide-assists/src/lib.rs
index 8f0b8f861c..024448ef1e 100644
--- a/crates/ide-assists/src/lib.rs
+++ b/crates/ide-assists/src/lib.rs
@@ -217,6 +217,7 @@ mod handlers {
     mod unwrap_result_return_type;
     mod unwrap_tuple;
     mod wrap_return_type_in_result;
+    mod wrap_unwrap_cfg_attr;
 
     pub(crate) fn all() -> &'static [Handler] {
         &[
@@ -342,6 +343,8 @@ mod handlers {
             unwrap_tuple::unwrap_tuple,
             unqualify_method_call::unqualify_method_call,
             wrap_return_type_in_result::wrap_return_type_in_result,
+            wrap_unwrap_cfg_attr::wrap_unwrap_cfg_attr,
+
             // These are manually sorted for better priorities. By default,
             // priority is determined by the size of the target range (smaller
             // target wins). If the ranges are equal, position in this list is


Test patch:
diff --git a/crates/ide-assists/src/tests/generated.rs b/crates/ide-assists/src/tests/generated.rs
index a66e199a75..2bf0934767 100644
--- a/crates/ide-assists/src/tests/generated.rs
+++ b/crates/ide-assists/src/tests/generated.rs
@@ -3151,3 +3151,22 @@ fn foo() -> Result<i32, ${0:_}> { Ok(42i32) }
 "#####,
     )
 }
+
+#[test]
+fn doctest_wrap_unwrap_cfg_attr() {
+    check_doc_test(
+        "wrap_unwrap_cfg_attr",
+        r#####"
+#[derive$0(Debug)]
+struct S {
+   field: i32
+}
+"#####,
+        r#####"
+#[cfg_attr($0, derive(Debug))]
+struct S {
+   field: i32
+}
+"#####,
+    )
+}