1 files changed, 318 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/merge_imports.rs b/crates/assists/src/handlers/merge_imports.rs
new file mode 100644
index 000000000..35b884206
--- /dev/null
+++ b/crates/assists/src/handlers/merge_imports.rs
@@ -0,0 +1,318 @@
+use std::iter::successors;
+
+use syntax::{
+    algo::{neighbor, skip_trivia_token, SyntaxRewriter},
+    ast::{self, edit::AstNodeEdit, make},
+    AstNode, Direction, InsertPosition, SyntaxElement, T,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::next_prev,
+    AssistId, AssistKind,
+};
+
+// Assist: merge_imports
+//
+// Merges two imports with a common prefix.
+//
+// ```
+// use std::<|>fmt::Formatter;
+// use std::io;
+// ```
+// ->
+// ```
+// use std::{fmt::Formatter, io};
+// ```
+pub(crate) fn merge_imports(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let tree: ast::UseTree = ctx.find_node_at_offset()?;
+    let mut rewriter = SyntaxRewriter::default();
+    let mut offset = ctx.offset();
+
+    if let Some(use_item) = tree.syntax().parent().and_then(ast::Use::cast) {
+        let (merged, to_delete) = next_prev()
+            .filter_map(|dir| neighbor(&use_item, dir))
+            .filter_map(|it| Some((it.clone(), it.use_tree()?)))
+            .find_map(|(use_item, use_tree)| {
+                Some((try_merge_trees(&tree, &use_tree)?, use_item))
+            })?;
+
+        rewriter.replace_ast(&tree, &merged);
+        rewriter += to_delete.remove();
+
+        if to_delete.syntax().text_range().end() < offset {
+            offset -= to_delete.syntax().text_range().len();
+        }
+    } else {
+        let (merged, to_delete) = next_prev()
+            .filter_map(|dir| neighbor(&tree, dir))
+            .find_map(|use_tree| Some((try_merge_trees(&tree, &use_tree)?, use_tree.clone())))?;
+
+        rewriter.replace_ast(&tree, &merged);
+        rewriter += to_delete.remove();
+
+        if to_delete.syntax().text_range().end() < offset {
+            offset -= to_delete.syntax().text_range().len();
+        }
+    };
+
+    let target = tree.syntax().text_range();
+    acc.add(
+        AssistId("merge_imports", AssistKind::RefactorRewrite),
+        "Merge imports",
+        target,
+        |builder| {
+            builder.rewrite(rewriter);
+        },
+    )
+}
+
+fn try_merge_trees(old: &ast::UseTree, new: &ast::UseTree) -> Option<ast::UseTree> {
+    let lhs_path = old.path()?;
+    let rhs_path = new.path()?;
+
+    let (lhs_prefix, rhs_prefix) = common_prefix(&lhs_path, &rhs_path)?;
+
+    let lhs = old.split_prefix(&lhs_prefix);
+    let rhs = new.split_prefix(&rhs_prefix);
+
+    let should_insert_comma = lhs
+        .use_tree_list()?
+        .r_curly_token()
+        .and_then(|it| skip_trivia_token(it.prev_token()?, Direction::Prev))
+        .map(|it| it.kind() != T![,])
+        .unwrap_or(true);
+
+    let mut to_insert: Vec<SyntaxElement> = Vec::new();
+    if should_insert_comma {
+        to_insert.push(make::token(T![,]).into());
+        to_insert.push(make::tokens::single_space().into());
+    }
+    to_insert.extend(
+        rhs.use_tree_list()?
+            .syntax()
+            .children_with_tokens()
+            .filter(|it| it.kind() != T!['{'] && it.kind() != T!['}']),
+    );
+    let use_tree_list = lhs.use_tree_list()?;
+    let pos = InsertPosition::Before(use_tree_list.r_curly_token()?.into());
+    let use_tree_list = use_tree_list.insert_children(pos, to_insert);
+    Some(lhs.with_use_tree_list(use_tree_list))
+}
+
+fn common_prefix(lhs: &ast::Path, rhs: &ast::Path) -> Option<(ast::Path, ast::Path)> {
+    let mut res = None;
+    let mut lhs_curr = first_path(&lhs);
+    let mut rhs_curr = first_path(&rhs);
+    loop {
+        match (lhs_curr.segment(), rhs_curr.segment()) {
+            (Some(lhs), Some(rhs)) if lhs.syntax().text() == rhs.syntax().text() => (),
+            _ => break,
+        }
+        res = Some((lhs_curr.clone(), rhs_curr.clone()));
+
+        match (lhs_curr.parent_path(), rhs_curr.parent_path()) {
+            (Some(lhs), Some(rhs)) => {
+                lhs_curr = lhs;
+                rhs_curr = rhs;
+            }
+            _ => break,
+        }
+    }
+
+    res
+}
+
+fn first_path(path: &ast::Path) -> ast::Path {
+    successors(Some(path.clone()), |it| it.qualifier()).last().unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_merge_first() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt<|>::Debug;
+use std::fmt::Display;
+",
+            r"
+use std::fmt::{Debug, Display};
+",
+        )
+    }
+
+    #[test]
+    fn test_merge_second() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt::Debug;
+use std::fmt<|>::Display;
+",
+            r"
+use std::fmt::{Display, Debug};
+",
+        );
+    }
+
+    #[test]
+    fn merge_self1() {
+        check_assist(
+            merge_imports,
+            r"
+use std::fmt<|>;
+use std::fmt::Display;
+",
+            r"
+use std::fmt::{self, Display};
+",
+        );
+    }
+
+    #[test]
+    fn merge_self2() {
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt, <|>fmt::Display};
+",
+            r"
+use std::{fmt::{Display, self}};
+",
+        );
+    }
+
+    #[test]
+    fn test_merge_nested() {
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt<|>::Debug, fmt::Display};
+",
+            r"
+use std::{fmt::{Debug, Display}};
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+use std::{fmt::Debug, fmt<|>::Display};
+",
+            r"
+use std::{fmt::{Display, Debug}};
+",
+        );
+    }
+
+    #[test]
+    fn test_merge_single_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str;
+",
+            r"
+use std::{cell::*, str};
+",
+        )
+    }
+
+    #[test]
+    fn test_merge_both_wildcard_diff_prefixes() {
+        check_assist(
+            merge_imports,
+            r"
+use std<|>::cell::*;
+use std::str::*;
+",
+            r"
+use std::{cell::*, str::*};
+",
+        )
+    }
+
+    #[test]
+    fn removes_just_enough_whitespace() {
+        check_assist(
+            merge_imports,
+            r"
+use foo<|>::bar;
+use foo::baz;
+
+/// Doc comment
+",
+            r"
+use foo::{bar, baz};
+
+/// Doc comment
+",
+        );
+    }
+
+    #[test]
+    fn works_with_trailing_comma() {
+        check_assist(
+            merge_imports,
+            r"
+use {
+    foo<|>::bar,
+    foo::baz,
+};
+",
+            r"
+use {
+    foo::{bar, baz},
+};
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+use {
+    foo::baz,
+    foo<|>::bar,
+};
+",
+            r"
+use {
+    foo::{bar, baz},
+};
+",
+        );
+    }
+
+    #[test]
+    fn test_double_comma() {
+        check_assist(
+            merge_imports,
+            r"
+use foo::bar::baz;
+use foo::<|>{
+    FooBar,
+};
+",
+            r"
+use foo::{
+    FooBar,
+bar::baz};
+",
+        )
+    }
+
+    #[test]
+    fn test_empty_use() {
+        check_assist_not_applicable(
+            merge_imports,
+            r"
+use std::<|>
+fn main() {}",
+        );
+    }
+}