3 files changed, 280 insertions, 0 deletions

diff --git a/crates/ide_assists/src/handlers/convert_iter_for_each_to_for.rs b/crates/ide_assists/src/handlers/convert_iter_for_each_to_for.rs
new file mode 100644
index 000000000..4e75a7b14
--- /dev/null
+++ b/crates/ide_assists/src/handlers/convert_iter_for_each_to_for.rs
@@ -0,0 +1,248 @@
+use ide_db::helpers::FamousDefs;
+use syntax::{
+    ast::{self, edit::AstNodeEdit, make, ArgListOwner},
+    AstNode,
+};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+// Assist: convert_iter_for_each_to_for
+//
+// Converts an Iterator::for_each function into a for loop.
+//
+// ```
+// # //- /lib.rs crate:core
+// # pub mod iter { pub mod traits { pub mod iterator { pub trait Iterator {} } } }
+// # pub struct SomeIter;
+// # impl self::iter::traits::iterator::Iterator for SomeIter {}
+// # //- /lib.rs crate:main deps:core
+// # use core::SomeIter;
+// fn main() {
+//     let iter = SomeIter;
+//     iter.for_each$0(|(x, y)| {
+//         println!("x: {}, y: {}", x, y);
+//     });
+// }
+// ```
+// ->
+// ```
+// # use core::SomeIter;
+// fn main() {
+//     let iter = SomeIter;
+//     for (x, y) in iter {
+//         println!("x: {}, y: {}", x, y);
+//     }
+// }
+// ```
+
+pub(crate) fn convert_iter_for_each_to_for(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let method = ctx.find_node_at_offset::<ast::MethodCallExpr>()?;
+
+    let closure = match method.arg_list()?.args().next()? {
+        ast::Expr::ClosureExpr(expr) => expr,
+        _ => return None,
+    };
+
+    let (method, receiver) = validate_method_call_expr(ctx, method)?;
+
+    let param_list = closure.param_list()?;
+    let param = param_list.params().next()?.pat()?;
+    let body = closure.body()?;
+
+    let stmt = method.syntax().parent().and_then(ast::ExprStmt::cast);
+    let syntax = stmt.as_ref().map_or(method.syntax(), |stmt| stmt.syntax());
+
+    acc.add(
+        AssistId("convert_iter_for_each_to_for", AssistKind::RefactorRewrite),
+        "Replace this `Iterator::for_each` with a for loop",
+        syntax.text_range(),
+        |builder| {
+            let indent = stmt.as_ref().map_or(method.indent_level(), |stmt| stmt.indent_level());
+
+            let block = match body {
+                ast::Expr::BlockExpr(block) => block,
+                _ => make::block_expr(Vec::new(), Some(body)),
+            }
+            .reset_indent()
+            .indent(indent);
+
+            let expr_for_loop = make::expr_for_loop(param, receiver, block);
+            builder.replace(syntax.text_range(), expr_for_loop.syntax().text())
+        },
+    )
+}
+
+fn validate_method_call_expr(
+    ctx: &AssistContext,
+    expr: ast::MethodCallExpr,
+) -> Option<(ast::Expr, ast::Expr)> {
+    let name_ref = expr.name_ref()?;
+    if name_ref.syntax().text_range().intersect(ctx.frange.range).is_none()
+        || name_ref.text() != "for_each"
+    {
+        return None;
+    }
+
+    let sema = &ctx.sema;
+
+    let receiver = expr.receiver()?;
+    let expr = ast::Expr::MethodCallExpr(expr);
+
+    let it_type = sema.type_of_expr(&receiver)?;
+    let module = sema.scope(receiver.syntax()).module()?;
+    let krate = module.krate();
+
+    let iter_trait = FamousDefs(sema, Some(krate)).core_iter_Iterator()?;
+    it_type.impls_trait(sema.db, iter_trait, &[]).then(|| (expr, receiver))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{self, check_assist};
+
+    use super::*;
+
+    const EMPTY_ITER_FIXTURE: &'static str = r"
+//- /lib.rs deps:core crate:empty_iter
+pub struct EmptyIter;
+impl Iterator for EmptyIter {
+    type Item = usize;
+    fn next(&mut self) -> Option<Self::Item> { None }
+}
+pub struct Empty;
+impl Empty {
+    pub fn iter(&self) -> EmptyIter { EmptyIter }
+}
+";
+
+    fn check_assist_with_fixtures(before: &str, after: &str) {
+        let before = &format!(
+            "//- /main.rs crate:main deps:core,empty_iter{}{}{}",
+            before,
+            EMPTY_ITER_FIXTURE,
+            FamousDefs::FIXTURE,
+        );
+        check_assist(convert_iter_for_each_to_for, before, after);
+    }
+
+    fn check_assist_not_applicable(before: &str) {
+        let before = &format!(
+            "//- /main.rs crate:main deps:core,empty_iter{}{}{}",
+            before,
+            EMPTY_ITER_FIXTURE,
+            FamousDefs::FIXTURE,
+        );
+        tests::check_assist_not_applicable(convert_iter_for_each_to_for, before);
+    }
+
+    #[test]
+    fn test_for_each_in_method_stmt() {
+        check_assist_with_fixtures(
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    x.iter().$0for_each(|(x, y)| {
+        println!("x: {}, y: {}", x, y);
+    });
+}"#,
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    for (x, y) in x.iter() {
+        println!("x: {}, y: {}", x, y);
+    }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_for_each_in_method() {
+        check_assist_with_fixtures(
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    x.iter().$0for_each(|(x, y)| {
+        println!("x: {}, y: {}", x, y);
+    })
+}"#,
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    for (x, y) in x.iter() {
+        println!("x: {}, y: {}", x, y);
+    }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_for_each_in_iter_stmt() {
+        check_assist_with_fixtures(
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty.iter();
+    x.$0for_each(|(x, y)| {
+        println!("x: {}, y: {}", x, y);
+    });
+}"#,
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty.iter();
+    for (x, y) in x {
+        println!("x: {}, y: {}", x, y);
+    }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_for_each_without_braces_stmt() {
+        check_assist_with_fixtures(
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    x.iter().$0for_each(|(x, y)| println!("x: {}, y: {}", x, y));
+}"#,
+            r#"
+use empty_iter::*;
+fn main() {
+    let x = Empty;
+    for (x, y) in x.iter() {
+        println!("x: {}, y: {}", x, y)
+    }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn test_for_each_not_applicable() {
+        check_assist_not_applicable(
+            r#"
+fn main() {
+    ().$0for_each(|x| println!("{}", x));
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_for_each_not_applicable_invalid_cursor_pos() {
+        check_assist_not_applicable(
+            r#"
+use empty_iter::*;
+fn main() {
+    Empty.iter().for_each(|(x, y)| $0println!("x: {}, y: {}", x, y));
+}"#,
+        )
+    }
+}
diff --git a/crates/ide_assists/src/lib.rs b/crates/ide_assists/src/lib.rs
index ea62d5f5d..f1aab74d4 100644
--- a/crates/ide_assists/src/lib.rs
+++ b/crates/ide_assists/src/lib.rs
@@ -116,6 +116,7 @@ mod handlers {
     mod change_visibility;
     mod convert_integer_literal;
     mod convert_comment_block;
+    mod convert_iter_for_each_to_for;
     mod early_return;
     mod expand_glob_import;
     mod extract_function;
@@ -181,6 +182,7 @@ mod handlers {
             change_visibility::change_visibility,
             convert_integer_literal::convert_integer_literal,
             convert_comment_block::convert_comment_block,
+            convert_iter_for_each_to_for::convert_iter_for_each_to_for,
             early_return::convert_to_guarded_return,
             expand_glob_import::expand_glob_import,
             extract_struct_from_enum_variant::extract_struct_from_enum_variant,
diff --git a/crates/ide_assists/src/tests/generated.rs b/crates/ide_assists/src/tests/generated.rs
index 304b5798f..3f77edd8d 100644
--- a/crates/ide_assists/src/tests/generated.rs
+++ b/crates/ide_assists/src/tests/generated.rs
@@ -206,6 +206,36 @@ const _: i32 = 0b1010;
 }
 
 #[test]
+fn doctest_convert_iter_for_each_to_for() {
+    check_doc_test(
+        "convert_iter_for_each_to_for",
+        r#####"
+//- /lib.rs crate:core
+pub mod iter { pub mod traits { pub mod iterator { pub trait Iterator {} } } }
+pub struct SomeIter;
+impl self::iter::traits::iterator::Iterator for SomeIter {}
+//- /lib.rs crate:main deps:core
+use core::SomeIter;
+fn main() {
+    let iter = SomeIter;
+    iter.for_each$0(|(x, y)| {
+        println!("x: {}, y: {}", x, y);
+    });
+}
+"#####,
+        r#####"
+use core::SomeIter;
+fn main() {
+    let iter = SomeIter;
+    for (x, y) in iter {
+        println!("x: {}, y: {}", x, y);
+    }
+}
+"#####,
+    )
+}
+
+#[test]
 fn doctest_convert_to_guarded_return() {
     check_doc_test(
         "convert_to_guarded_return",