2 files changed, 732 insertions, 0 deletions

diff --git a/crates/ra_assists/src/auto_import.rs b/crates/ra_assists/src/auto_import.rs
new file mode 100644
index 000000000..6a0c351f1
--- /dev/null
+++ b/crates/ra_assists/src/auto_import.rs
@@ -0,0 +1,729 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    ast, AstNode, SyntaxNode, Direction, TextRange,
+    SyntaxKind::{ PATH, PATH_SEGMENT, COLONCOLON, COMMA }
+};
+use crate::assist_ctx::{AssistCtx, Assist, AssistBuilder};
+
+fn collect_path_segments(path: &ast::Path) -> Option<Vec<&ast::PathSegment>> {
+    let mut v = Vec::new();
+    collect_path_segments_raw(&mut v, path)?;
+    return Some(v);
+}
+
+fn collect_path_segments_raw<'a>(
+    segments: &mut Vec<&'a ast::PathSegment>,
+    mut path: &'a ast::Path,
+) -> Option<usize> {
+    let oldlen = segments.len();
+    loop {
+        let mut children = path.syntax().children();
+        let (first, second, third) = (
+            children.next().map(|n| (n, n.kind())),
+            children.next().map(|n| (n, n.kind())),
+            children.next().map(|n| (n, n.kind())),
+        );
+        match (first, second, third) {
+            (Some((subpath, PATH)), Some((_, COLONCOLON)), Some((segment, PATH_SEGMENT))) => {
+                path = ast::Path::cast(subpath)?;
+                segments.push(ast::PathSegment::cast(segment)?);
+            }
+            (Some((segment, PATH_SEGMENT)), _, _) => {
+                segments.push(ast::PathSegment::cast(segment)?);
+                break;
+            }
+            (_, _, _) => return None,
+        }
+    }
+    // We need to reverse only the new added segments
+    let only_new_segments = segments.split_at_mut(oldlen).1;
+    only_new_segments.reverse();
+    return Some(segments.len() - oldlen);
+}
+
+fn fmt_segments(segments: &[&ast::PathSegment]) -> String {
+    let mut buf = String::new();
+    fmt_segments_raw(segments, &mut buf);
+    return buf;
+}
+
+fn fmt_segments_raw(segments: &[&ast::PathSegment], buf: &mut String) {
+    let mut first = true;
+    for s in segments {
+        if !first {
+            buf.push_str("::");
+        }
+        match s.kind() {
+            Some(ast::PathSegmentKind::Name(nameref)) => buf.push_str(nameref.text()),
+            Some(ast::PathSegmentKind::SelfKw) => buf.push_str("self"),
+            Some(ast::PathSegmentKind::SuperKw) => buf.push_str("super"),
+            Some(ast::PathSegmentKind::CrateKw) => buf.push_str("crate"),
+            None => {}
+        }
+        first = false;
+    }
+}
+
+// Returns the numeber of common segments.
+fn compare_path_segments(left: &[&ast::PathSegment], right: &[&ast::PathSegment]) -> usize {
+    return left.iter().zip(right).filter(|(l, r)| compare_path_segment(l, r)).count();
+}
+
+fn compare_path_segment(a: &ast::PathSegment, b: &ast::PathSegment) -> bool {
+    if let (Some(ka), Some(kb)) = (a.kind(), b.kind()) {
+        match (ka, kb) {
+            (ast::PathSegmentKind::Name(nameref_a), ast::PathSegmentKind::Name(nameref_b)) => {
+                nameref_a.text() == nameref_b.text()
+            }
+            (ast::PathSegmentKind::SelfKw, ast::PathSegmentKind::SelfKw) => true,
+            (ast::PathSegmentKind::SuperKw, ast::PathSegmentKind::SuperKw) => true,
+            (ast::PathSegmentKind::CrateKw, ast::PathSegmentKind::CrateKw) => true,
+            (_, _) => false,
+        }
+    } else {
+        false
+    }
+}
+
+fn compare_path_segment_with_name(a: &ast::PathSegment, b: &ast::Name) -> bool {
+    if let Some(ka) = a.kind() {
+        return match (ka, b) {
+            (ast::PathSegmentKind::Name(nameref_a), _) => nameref_a.text() == b.text(),
+            (_, _) => false,
+        };
+    } else {
+        false
+    }
+}
+
+#[derive(Copy, Clone)]
+enum ImportAction<'a> {
+    Nothing,
+    // Add a brand new use statement.
+    AddNewUse {
+        anchor: Option<&'a SyntaxNode>, // anchor node
+        add_after_anchor: bool,
+    },
+
+    // To split an existing use statement creating a nested import.
+    AddNestedImport {
+        // how may segments matched with the target path
+        common_segments: usize,
+        path_to_split: &'a ast::Path,
+        // the first segment of path_to_split we want to add into the new nested list
+        first_segment_to_split: Option<&'a ast::PathSegment>,
+        // Wether to add 'self' in addition to the target path
+        add_self: bool,
+    },
+    // To add the target path to an existing nested import tree list.
+    AddInTreeList {
+        common_segments: usize,
+        // The UseTreeList where to add the target path
+        tree_list: &'a ast::UseTreeList,
+        add_self: bool,
+    },
+}
+
+impl<'a> ImportAction<'a> {
+    fn add_new_use(anchor: Option<&'a SyntaxNode>, add_after_anchor: bool) -> Self {
+        ImportAction::AddNewUse { anchor, add_after_anchor }
+    }
+
+    fn add_nested_import(
+        common_segments: usize,
+        path_to_split: &'a ast::Path,
+        first_segment_to_split: Option<&'a ast::PathSegment>,
+        add_self: bool,
+    ) -> Self {
+        ImportAction::AddNestedImport {
+            common_segments,
+            path_to_split,
+            first_segment_to_split,
+            add_self,
+        }
+    }
+
+    fn add_in_tree_list(
+        common_segments: usize,
+        tree_list: &'a ast::UseTreeList,
+        add_self: bool,
+    ) -> Self {
+        ImportAction::AddInTreeList { common_segments, tree_list, add_self }
+    }
+
+    fn better<'b>(left: &'b ImportAction<'a>, right: &'b ImportAction<'a>) -> &'b ImportAction<'a> {
+        if left.is_better(right) {
+            left
+        } else {
+            right
+        }
+    }
+
+    fn is_better(&self, other: &ImportAction) -> bool {
+        match (self, other) {
+            (ImportAction::Nothing, _) => true,
+            (ImportAction::AddInTreeList { .. }, ImportAction::Nothing) => false,
+            (
+                ImportAction::AddNestedImport { common_segments: n, .. },
+                ImportAction::AddInTreeList { common_segments: m, .. },
+            ) => n > m,
+            (
+                ImportAction::AddInTreeList { common_segments: n, .. },
+                ImportAction::AddNestedImport { common_segments: m, .. },
+            ) => n > m,
+            (ImportAction::AddInTreeList { .. }, _) => true,
+            (ImportAction::AddNestedImport { .. }, ImportAction::Nothing) => false,
+            (ImportAction::AddNestedImport { .. }, _) => true,
+            (ImportAction::AddNewUse { .. }, _) => false,
+        }
+    }
+}
+
+// Find out the best ImportAction to import target path against current_use_tree.
+// If current_use_tree has a nested import the function gets called recursively on every UseTree inside a UseTreeList.
+fn walk_use_tree_for_best_action<'a>(
+    current_path_segments: &mut Vec<&'a ast::PathSegment>, // buffer containing path segments
+    current_parent_use_tree_list: Option<&'a ast::UseTreeList>, // will be Some value if we are in a nested import
+    current_use_tree: &'a ast::UseTree, // the use tree we are currently examinating
+    target: &[&'a ast::PathSegment],    // the path we want to import
+) -> ImportAction<'a> {
+    // We save the number of segments in the buffer so we can restore the correct segments
+    // before returning. Recursive call will add segments so we need to delete them.
+    let prev_len = current_path_segments.len();
+
+    let tree_list = current_use_tree.use_tree_list();
+    let alias = current_use_tree.alias();
+
+    let path = match current_use_tree.path() {
+        Some(path) => path,
+        None => {
+            // If the use item don't have a path, it means it's broken (syntax error)
+            return ImportAction::add_new_use(
+                current_use_tree
+                    .syntax()
+                    .ancestors()
+                    .find_map(ast::UseItem::cast)
+                    .map(AstNode::syntax),
+                true,
+            );
+        }
+    };
+
+    // This can happen only if current_use_tree is a direct child of a UseItem
+    if let Some(name) = alias.and_then(ast::NameOwner::name) {
+        if compare_path_segment_with_name(target[0], name) {
+            return ImportAction::Nothing;
+        }
+    }
+
+    collect_path_segments_raw(current_path_segments, path);
+
+    // We compare only the new segments added in the line just above.
+    // The first prev_len segments were already compared in 'parent' recursive calls.
+    let left = target.split_at(prev_len).1;
+    let right = current_path_segments.split_at(prev_len).1;
+    let common = compare_path_segments(left, right);
+    let mut action = match common {
+        0 => ImportAction::add_new_use(
+            // e.g: target is std::fmt and we can have
+            // use foo::bar
+            // We add a brand new use statement
+            current_use_tree.syntax().ancestors().find_map(ast::UseItem::cast).map(AstNode::syntax),
+            true,
+        ),
+        common if common == left.len() && left.len() == right.len() => {
+            // e.g: target is std::fmt and we can have
+            // 1- use std::fmt;
+            // 2- use std::fmt:{ ... }
+            if let Some(list) = tree_list {
+                // In case 2 we need to add self to the nested list
+                // unless it's already there
+                let has_self = list.use_trees().map(ast::UseTree::path).any(|p| {
+                    p.and_then(ast::Path::segment)
+                        .and_then(ast::PathSegment::kind)
+                        .filter(|k| *k == ast::PathSegmentKind::SelfKw)
+                        .is_some()
+                });
+
+                if has_self {
+                    ImportAction::Nothing
+                } else {
+                    ImportAction::add_in_tree_list(current_path_segments.len(), list, true)
+                }
+            } else {
+                // Case 1
+                ImportAction::Nothing
+            }
+        }
+        common if common != left.len() && left.len() == right.len() => {
+            // e.g: target is std::fmt and we have
+            // use std::io;
+            // We need to split.
+            let segments_to_split = current_path_segments.split_at(prev_len + common).1;
+            ImportAction::add_nested_import(
+                prev_len + common,
+                path,
+                Some(segments_to_split[0]),
+                false,
+            )
+        }
+        common if left.len() > right.len() => {
+            // e.g: target is std::fmt and we can have
+            // 1- use std;
+            // 2- use std::{ ... };
+
+            // fallback action
+            let mut better_action = ImportAction::add_new_use(
+                current_use_tree
+                    .syntax()
+                    .ancestors()
+                    .find_map(ast::UseItem::cast)
+                    .map(AstNode::syntax),
+                true,
+            );
+            if let Some(list) = tree_list {
+                // Case 2, check recursively if the path is already imported in the nested list
+                for u in list.use_trees() {
+                    let child_action =
+                        walk_use_tree_for_best_action(current_path_segments, Some(list), u, target);
+                    if child_action.is_better(&better_action) {
+                        better_action = child_action;
+                        if let ImportAction::Nothing = better_action {
+                            return better_action;
+                        }
+                    }
+                }
+            } else {
+                // Case 1, split
+                better_action = ImportAction::add_nested_import(prev_len + common, path, None, true)
+            }
+            better_action
+        }
+        common if left.len() < right.len() => {
+            // e.g: target is std::fmt and we can have
+            // use std::fmt::Debug;
+            let segments_to_split = current_path_segments.split_at(prev_len + common).1;
+            ImportAction::add_nested_import(
+                prev_len + common,
+                path,
+                Some(segments_to_split[0]),
+                true,
+            )
+        }
+        _ => unreachable!(),
+    };
+
+    // If we are inside a UseTreeList adding a use statement become adding to the existing
+    // tree list.
+    action = match (current_parent_use_tree_list, action) {
+        (Some(use_tree_list), ImportAction::AddNewUse { .. }) => {
+            ImportAction::add_in_tree_list(prev_len, use_tree_list, false)
+        }
+        (_, _) => action,
+    };
+
+    // We remove the segments added
+    current_path_segments.truncate(prev_len);
+    return action;
+}
+
+fn best_action_for_target<'b, 'a: 'b>(
+    container: &'a SyntaxNode,
+    path: &'a ast::Path,
+    target: &'b [&'a ast::PathSegment],
+) -> ImportAction<'a> {
+    let mut storage = Vec::with_capacity(16); // this should be the only allocation
+    let best_action = container
+        .children()
+        .filter_map(ast::UseItem::cast)
+        .filter_map(ast::UseItem::use_tree)
+        .map(|u| walk_use_tree_for_best_action(&mut storage, None, u, target))
+        .fold(None, |best, a| {
+            best.and_then(|best| Some(*ImportAction::better(&best, &a))).or(Some(a))
+        });
+
+    match best_action {
+        Some(action) => return action,
+        None => {
+            // We have no action we no use item was found in container so we find
+            // another item and we use it as anchor.
+            // If there are not items, we choose the target path itself as anchor.
+            let anchor = container
+                .children()
+                .find_map(ast::ModuleItem::cast)
+                .map(AstNode::syntax)
+                .or(Some(path.syntax()));
+
+            return ImportAction::add_new_use(anchor, false);
+        }
+    }
+}
+
+fn make_assist(action: &ImportAction, target: &[&ast::PathSegment], edit: &mut AssistBuilder) {
+    match action {
+        ImportAction::AddNewUse { anchor, add_after_anchor } => {
+            make_assist_add_new_use(anchor, *add_after_anchor, target, edit)
+        }
+        ImportAction::AddInTreeList { common_segments, tree_list, add_self } => {
+            // We know that the fist n segments already exists in the use statement we want
+            // to modify, so we want to add only the last target.len() - n segments.
+            let segments_to_add = target.split_at(*common_segments).1;
+            make_assist_add_in_tree_list(tree_list, segments_to_add, *add_self, edit)
+        }
+        ImportAction::AddNestedImport {
+            common_segments,
+            path_to_split,
+            first_segment_to_split,
+            add_self,
+        } => {
+            let segments_to_add = target.split_at(*common_segments).1;
+            make_assist_add_nested_import(
+                path_to_split,
+                first_segment_to_split,
+                segments_to_add,
+                *add_self,
+                edit,
+            )
+        }
+        _ => {}
+    }
+}
+
+fn make_assist_add_new_use(
+    anchor: &Option<&SyntaxNode>,
+    after: bool,
+    target: &[&ast::PathSegment],
+    edit: &mut AssistBuilder,
+) {
+    if let Some(anchor) = anchor {
+        let indent = ra_fmt::leading_indent(anchor);
+        let mut buf = String::new();
+        if after {
+            buf.push_str("\n");
+            if let Some(spaces) = indent {
+                buf.push_str(spaces);
+            }
+        }
+        buf.push_str("use ");
+        fmt_segments_raw(target, &mut buf);
+        buf.push_str(";");
+        if !after {
+            buf.push_str("\n\n");
+            if let Some(spaces) = indent {
+                buf.push_str(spaces);
+            }
+        }
+        let position = if after { anchor.range().end() } else { anchor.range().start() };
+        edit.insert(position, buf);
+    }
+}
+
+fn make_assist_add_in_tree_list(
+    tree_list: &ast::UseTreeList,
+    target: &[&ast::PathSegment],
+    add_self: bool,
+    edit: &mut AssistBuilder,
+) {
+    let last = tree_list.use_trees().last();
+    if let Some(last) = last {
+        let mut buf = String::new();
+        let comma = last.syntax().siblings(Direction::Next).find(|n| n.kind() == COMMA);
+        let offset = if let Some(comma) = comma {
+            comma.range().end()
+        } else {
+            buf.push_str(",");
+            last.syntax().range().end()
+        };
+        if add_self {
+            buf.push_str(" self")
+        } else {
+            buf.push_str(" ");
+        }
+        fmt_segments_raw(target, &mut buf);
+        edit.insert(offset, buf);
+    } else {
+
+    }
+}
+
+fn make_assist_add_nested_import(
+    path: &ast::Path,
+    first_segment_to_split: &Option<&ast::PathSegment>,
+    target: &[&ast::PathSegment],
+    add_self: bool,
+    edit: &mut AssistBuilder,
+) {
+    let use_tree = path.syntax().ancestors().find_map(ast::UseTree::cast);
+    if let Some(use_tree) = use_tree {
+        let (start, add_colon_colon) = if let Some(first_segment_to_split) = first_segment_to_split
+        {
+            (first_segment_to_split.syntax().range().start(), false)
+        } else {
+            (use_tree.syntax().range().end(), true)
+        };
+        let end = use_tree.syntax().range().end();
+
+        let mut buf = String::new();
+        if add_colon_colon {
+            buf.push_str("::");
+        }
+        buf.push_str("{ ");
+        if add_self {
+            buf.push_str("self, ");
+        }
+        fmt_segments_raw(target, &mut buf);
+        if !target.is_empty() {
+            buf.push_str(", ");
+        }
+        edit.insert(start, buf);
+        edit.insert(end, "}");
+    }
+}
+
+pub(crate) fn auto_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let node = ctx.covering_node();
+    let current_file = node.ancestors().find_map(ast::SourceFile::cast)?;
+
+    let path = node.ancestors().find_map(ast::Path::cast)?;
+    // We don't want to mess with use statements
+    if path.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
+        return None;
+    }
+
+    let segments = collect_path_segments(path)?;
+    if segments.len() < 2 {
+        return None;
+    }
+
+    ctx.build(format!("import {} in the current file", fmt_segments(&segments)), |edit| {
+        let action = best_action_for_target(current_file.syntax(), path, &segments);
+        make_assist(&action, segments.as_slice(), edit);
+        if let Some(last_segment) = path.segment() {
+            // Here we are assuming the assist will provide a  correct use statement
+            // so we can delete the path qualifier
+            edit.delete(TextRange::from_to(
+                path.syntax().range().start(),
+                last_segment.syntax().range().start(),
+            ));
+        }
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{ check_assist, check_assist_not_applicable };
+
+    #[test]
+    fn test_auto_import_file_add_use_no_anchor() {
+        check_assist(
+            auto_import,
+            "
+std::fmt::Debug<|>
+    ",
+            "
+use std::fmt::Debug;
+
+Debug<|>
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_use() {
+        check_assist(
+            auto_import,
+            "
+use stdx;
+
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            "
+use stdx;
+use std::fmt::Debug;
+
+impl Debug<|> for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_use_other_anchor() {
+        check_assist(
+            auto_import,
+            "
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            "
+use std::fmt::Debug;
+
+impl Debug<|> for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_use_other_anchor_indent() {
+        check_assist(
+            auto_import,
+            "
+    impl std::fmt::Debug<|> for Foo {
+    }
+    ",
+            "
+    use std::fmt::Debug;
+
+    impl Debug<|> for Foo {
+    }
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_split_different() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt;
+
+impl std::io<|> for Foo {
+}
+    ",
+            "
+use std::{ io, fmt};
+
+impl io<|> for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_split_self_for_use() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt;
+
+impl std::fmt::Debug<|> for Foo {
+}
+    ",
+            "
+use std::fmt::{ self, Debug, };
+
+impl Debug<|> for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_split_self_for_target() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt::Debug;
+
+impl std::fmt<|> for Foo {
+}
+    ",
+            "
+use std::fmt::{ self, Debug};
+
+impl fmt<|> for Foo {
+}
+    ",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_to_nested_self_nested() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt::{Debug, nested::{Display}};
+
+impl std::fmt::nested<|> for Foo {
+}
+",
+            "
+use std::fmt::{Debug, nested::{Display, self}};
+
+impl nested<|> for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_to_nested_self_already_included() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt::{Debug, nested::{self, Display}};
+
+impl std::fmt::nested<|> for Foo {
+}
+",
+            "
+use std::fmt::{Debug, nested::{self, Display}};
+
+impl nested<|> for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_add_to_nested_nested() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt::{Debug, nested::{Display}};
+
+impl std::fmt::nested::Debug<|> for Foo {
+}
+",
+            "
+use std::fmt::{Debug, nested::{Display, Debug}};
+
+impl Debug<|> for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_file_alias() {
+        check_assist(
+            auto_import,
+            "
+use std::fmt as foo;
+
+impl foo::Debug<|> for Foo {
+}
+",
+            "
+use std::fmt as foo;
+
+impl Debug<|> for Foo {
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_auto_import_not_applicable_one_segment() {
+        check_assist_not_applicable(
+            auto_import,
+            "
+impl foo<|> for Foo {
+}
+",
+        );
+    }
+}
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 7928b4983..af578893e 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -84,6 +84,8 @@ mod introduce_variable;
 mod replace_if_let_with_match;
 mod split_import;
 mod remove_dbg;
+mod auto_import;
+
 fn all_assists<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assist>] {
     &[
         add_derive::add_derive,
@@ -95,6 +97,7 @@ fn all_assists<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assis
         replace_if_let_with_match::replace_if_let_with_match,
         split_import::split_import,
         remove_dbg::remove_dbg,
+        auto_import::auto_import,
     ]
 }