2 files changed, 140 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..3220f2f46
--- /dev/null
+++ b/crates/ide_assists/src/handlers/convert_iter_for_each_to_for.rs
@@ -0,0 +1,138 @@
+use ide_db::helpers::FamousDefs;
+use stdx::format_to;
+use syntax::{AstNode, ast::{self, ArgListOwner}};
+
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+
+/// Assist: convert_iter_for_each_to_for
+//
+/// Converts an Iterator::for_each function into a for loop.
+///
+/// ```rust
+/// fn main() {
+///     let vec = vec![(1, 2), (2, 3), (3, 4)];
+///     x.iter().for_each(|(x, y)| {
+///         println!("x: {}, y: {}", x, y);
+///    })
+/// }
+/// ```
+/// ->
+/// ```rust
+/// fn main() {
+///     let vec = vec![(1, 2), (2, 3), (3, 4)];
+///     for (x, y) in x.iter() {
+///         println!("x: {}, y: {}", x, y);
+///     });
+/// }
+/// ```
+pub(crate) fn convert_iter_for_each_to_for(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let closure;
+
+    let total_expr = match ctx.find_node_at_offset::<ast::Expr>()? {
+        ast::Expr::MethodCallExpr(expr) => {
+            closure = match expr.arg_list()?.args().next()? {
+                ast::Expr::ClosureExpr(expr) => expr,
+                _ => { return None; }
+            };
+            
+            expr
+        },
+        ast::Expr::ClosureExpr(expr) => {
+            closure = expr;
+            ast::MethodCallExpr::cast(closure.syntax().ancestors().nth(2)?)?
+        },
+        _ => { return None; }
+    };
+
+    let (total_expr, parent) = validate_method_call_expr(&ctx.sema, total_expr)?;
+
+    let param_list = closure.param_list()?;
+    let param = param_list.params().next()?;
+    let body = closure.body()?;
+
+    acc.add(
+        AssistId("convert_iter_for_each_to_for", AssistKind::RefactorRewrite),
+        "Replace this `Iterator::for_each` with a for loop",
+        total_expr.syntax().text_range(),
+        |builder| {
+            let mut buf = String::new();
+
+            format_to!(buf, "for {} in {} ", param, parent);
+
+            match body {
+                ast::Expr::BlockExpr(body) => format_to!(buf, "{}", body),
+                _ => format_to!(buf, "{{\n{}\n}}", body)
+            }
+
+            builder.replace(total_expr.syntax().text_range(), buf)
+        },
+    )
+}
+
+fn validate_method_call_expr(
+    sema: &hir::Semantics<ide_db::RootDatabase>,
+    expr: ast::MethodCallExpr,
+) -> Option<(ast::Expr, ast::Expr)> {
+    if expr.name_ref()?.text() != "for_each" {
+        return None;
+    }
+
+    let expr = ast::Expr::MethodCallExpr(expr);
+    let parent = ast::Expr::cast(expr.syntax().first_child()?)?;
+
+    let it_type = sema.type_of_expr(&parent)?;
+    let module = sema.scope(parent.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, parent))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_assist;
+
+    use super::*;
+
+    #[test]
+    fn test_for_each_in_method() {
+        check_assist(
+            convert_iter_for_each_to_for,
+            r"
+fn main() {
+    let x = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
+    x.iter().$0for_each(|(x, y)| {
+        dbg!(x, y)
+    });
+}",
+            r"
+fn main() {
+    let x = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
+    for (x, y) in x.iter() {
+        dbg!(x, y)
+    };
+}",
+        )
+    }
+
+    #[test]
+    fn test_for_each_in_closure() {
+        check_assist(
+            convert_iter_for_each_to_for,
+            r"
+fn main() {
+    let x = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
+    x.iter().for_each($0|(x, y)| {
+        dbg!(x, y)
+    });
+}",
+            r"
+fn main() {
+    let x = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
+    for (x, y) in x.iter() {
+        dbg!(x, y)
+    };
+}",
+        )
+    }
+}
\ No newline at end of file
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,