Merge #7130

7130: Add extract_assignment assist r=Jesse-Bakker a=Jesse-Bakker

Add extract-assignment assist (#7006).

Assist is for now only implemented on if/match-statements where the assigment is the last statement in every block,
as for other cases, one would have to check whether the assignment has effects on the rest of the block and
extract a temporary variable for it in the block.



Co-authored-by: Jesse Bakker <[email protected]>

1 files changed, 325 insertions, 0 deletions

diff --git a/crates/assists/src/handlers/extract_assignment.rs b/crates/assists/src/handlers/extract_assignment.rs
new file mode 100644
index 000000000..281cf5d24
--- /dev/null
+++ b/crates/assists/src/handlers/extract_assignment.rs
@@ -0,0 +1,325 @@
+use hir::AsName;
+use syntax::{
+    ast::{self, edit::AstNodeEdit, make},
+    AstNode,
+};
+use test_utils::mark;
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId, AssistKind,
+};
+
+// Assist: extract_assignment
+//
+// Extracts variable assigment to outside an if or match statement.
+//
+// ```
+// fn main() {
+//     let mut foo = 6;
+//
+//     if true {
+//         <|>foo = 5;
+//     } else {
+//         foo = 4;
+//     }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     let mut foo = 6;
+//
+//     foo = if true {
+//         5
+//     } else {
+//         4
+//     };
+// }
+// ```
+pub(crate) fn extract_assigment(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let name = ctx.find_node_at_offset::<ast::NameRef>()?.as_name();
+
+    let (old_stmt, new_stmt) = if let Some(if_expr) = ctx.find_node_at_offset::<ast::IfExpr>() {
+        (
+            ast::Expr::cast(if_expr.syntax().to_owned())?,
+            exprify_if(&if_expr, &name)?.indent(if_expr.indent_level()),
+        )
+    } else if let Some(match_expr) = ctx.find_node_at_offset::<ast::MatchExpr>() {
+        (ast::Expr::cast(match_expr.syntax().to_owned())?, exprify_match(&match_expr, &name)?)
+    } else {
+        return None;
+    };
+
+    let expr_stmt = make::expr_stmt(new_stmt);
+
+    acc.add(
+        AssistId("extract_assignment", AssistKind::RefactorExtract),
+        "Extract assignment",
+        old_stmt.syntax().text_range(),
+        move |edit| {
+            edit.replace(old_stmt.syntax().text_range(), format!("{} = {};", name, expr_stmt));
+        },
+    )
+}
+
+fn exprify_match(match_expr: &ast::MatchExpr, name: &hir::Name) -> Option<ast::Expr> {
+    let new_arm_list = match_expr
+        .match_arm_list()?
+        .arms()
+        .map(|arm| {
+            if let ast::Expr::BlockExpr(block) = arm.expr()? {
+                let new_block = exprify_block(&block, name)?.indent(block.indent_level());
+                Some(arm.replace_descendant(block, new_block))
+            } else {
+                None
+            }
+        })
+        .collect::<Option<Vec<_>>>()?;
+    let new_arm_list = match_expr
+        .match_arm_list()?
+        .replace_descendants(match_expr.match_arm_list()?.arms().zip(new_arm_list));
+    Some(make::expr_match(match_expr.expr()?, new_arm_list))
+}
+
+fn exprify_if(statement: &ast::IfExpr, name: &hir::Name) -> Option<ast::Expr> {
+    let then_branch = exprify_block(&statement.then_branch()?, name)?;
+    let else_branch = match statement.else_branch()? {
+        ast::ElseBranch::Block(ref block) => ast::ElseBranch::Block(exprify_block(block, name)?),
+        ast::ElseBranch::IfExpr(expr) => {
+            mark::hit!(test_extract_assigment_chained_if);
+            ast::ElseBranch::IfExpr(ast::IfExpr::cast(
+                exprify_if(&expr, name)?.syntax().to_owned(),
+            )?)
+        }
+    };
+    Some(make::expr_if(statement.condition()?, then_branch, Some(else_branch)))
+}
+
+fn exprify_block(block: &ast::BlockExpr, name: &hir::Name) -> Option<ast::BlockExpr> {
+    if block.expr().is_some() {
+        return None;
+    }
+
+    let mut stmts: Vec<_> = block.statements().collect();
+    let stmt = stmts.pop()?;
+
+    if let ast::Stmt::ExprStmt(stmt) = stmt {
+        if let ast::Expr::BinExpr(expr) = stmt.expr()? {
+            if expr.op_kind()? == ast::BinOp::Assignment
+                && &expr.lhs()?.name_ref()?.as_name() == name
+            {
+                // The last statement in the block is an assignment to the name we want
+                return Some(make::block_expr(stmts, Some(expr.rhs()?)));
+            }
+        }
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    #[test]
+    fn test_extract_assignment_if() {
+        check_assist(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    if true {
+        <|>a = 2;
+    } else {
+        a = 3;
+    }
+}"#,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    a = if true {
+        2
+    } else {
+        3
+    };
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_assignment_match() {
+        check_assist(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    match 1 {
+        1 => {
+            <|>a = 2;
+        },
+        2 => {
+            a = 3;
+        },
+        3 => {
+            a = 4;
+        }
+    }
+}"#,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    a = match 1 {
+        1 => {
+            2
+        },
+        2 => {
+            3
+        },
+        3 => {
+            4
+        }
+    };
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_assignment_not_last_not_applicable() {
+        check_assist_not_applicable(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    if true {
+        <|>a = 2;
+        b = a;
+    } else {
+        a = 3;
+    }
+}"#,
+        )
+    }
+
+    #[test]
+    fn test_extract_assignment_chained_if() {
+        mark::check!(test_extract_assigment_chained_if);
+        check_assist(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    if true {
+        <|>a = 2;
+    } else if false {
+        a = 3;
+    } else {
+        a = 4;
+    }
+}"#,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    a = if true {
+        2
+    } else if false {
+        3
+    } else {
+        4
+    };
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_assigment_retains_stmts() {
+        check_assist(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    if true {
+        let b = 2;
+        <|>a = 2;
+    } else {
+        let b = 3;
+        a = 3;
+    }
+}"#,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    a = if true {
+        let b = 2;
+        2
+    } else {
+        let b = 3;
+        3
+    };
+}"#,
+        )
+    }
+
+    #[test]
+    fn extract_assignment_let_stmt_not_applicable() {
+        check_assist_not_applicable(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    let b = if true {
+        <|>a = 2
+    } else {
+        a = 3
+    };
+}"#,
+        )
+    }
+
+    #[test]
+    fn extract_assignment_if_missing_assigment_not_applicable() {
+        check_assist_not_applicable(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    if true {
+        <|>a = 2;
+    } else {}
+}"#,
+        )
+    }
+
+    #[test]
+    fn extract_assignment_match_missing_assigment_not_applicable() {
+        check_assist_not_applicable(
+            extract_assigment,
+            r#"
+fn foo() {
+    let mut a = 1;
+
+    match 1 {
+        1 => {
+            <|>a = 2;
+        },
+        2 => {
+            a = 3;
+        },
+        3 => {},
+    }
+}"#,
+        )
+    }
+}