1 files changed, 432 insertions, 0 deletions

diff --git a/crates/ra_assists/src/introduce_variable.rs b/crates/ra_assists/src/introduce_variable.rs
new file mode 100644
index 000000000..c937a816c
--- /dev/null
+++ b/crates/ra_assists/src/introduce_variable.rs
@@ -0,0 +1,432 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    ast::{self, AstNode},
+    SyntaxKind::{
+        WHITESPACE, MATCH_ARM, LAMBDA_EXPR, PATH_EXPR, BREAK_EXPR, LOOP_EXPR, RETURN_EXPR, COMMENT
+    }, SyntaxNode, TextUnit,
+};
+
+use crate::{AssistCtx, Assist};
+
+pub(crate) fn introduce_variable<'a>(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let node = ctx.covering_node();
+    if !valid_covering_node(node) {
+        return None;
+    }
+    let expr = node.ancestors().filter_map(valid_target_expr).next()?;
+    let (anchor_stmt, wrap_in_block) = anchor_stmt(expr)?;
+    let indent = anchor_stmt.prev_sibling()?;
+    if indent.kind() != WHITESPACE {
+        return None;
+    }
+    ctx.build("introduce variable", move |edit| {
+        let mut buf = String::new();
+
+        let cursor_offset = if wrap_in_block {
+            buf.push_str("{ let var_name = ");
+            TextUnit::of_str("{ let ")
+        } else {
+            buf.push_str("let var_name = ");
+            TextUnit::of_str("let ")
+        };
+
+        expr.syntax().text().push_to(&mut buf);
+        let full_stmt = ast::ExprStmt::cast(anchor_stmt);
+        let is_full_stmt = if let Some(expr_stmt) = full_stmt {
+            Some(expr.syntax()) == expr_stmt.expr().map(|e| e.syntax())
+        } else {
+            false
+        };
+        if is_full_stmt {
+            if !full_stmt.unwrap().has_semi() {
+                buf.push_str(";");
+            }
+            edit.replace(expr.syntax().range(), buf);
+        } else {
+            buf.push_str(";");
+            indent.text().push_to(&mut buf);
+            edit.replace(expr.syntax().range(), "var_name".to_string());
+            edit.insert(anchor_stmt.range().start(), buf);
+            if wrap_in_block {
+                edit.insert(anchor_stmt.range().end(), " }");
+            }
+        }
+        edit.set_cursor(anchor_stmt.range().start() + cursor_offset);
+    })
+}
+
+fn valid_covering_node(node: &SyntaxNode) -> bool {
+    node.kind() != COMMENT
+}
+/// Check wether the node is a valid expression which can be extracted to a variable.
+/// In general that's true for any expression, but in some cases that would produce invalid code.
+fn valid_target_expr(node: &SyntaxNode) -> Option<&ast::Expr> {
+    return match node.kind() {
+        PATH_EXPR => None,
+        BREAK_EXPR => ast::BreakExpr::cast(node).and_then(|e| e.expr()),
+        RETURN_EXPR => ast::ReturnExpr::cast(node).and_then(|e| e.expr()),
+        LOOP_EXPR => ast::ReturnExpr::cast(node).and_then(|e| e.expr()),
+        _ => ast::Expr::cast(node),
+    };
+}
+
+/// Returns the syntax node which will follow the freshly introduced var
+/// and a boolean indicating whether we have to wrap it within a { } block
+/// to produce correct code.
+/// It can be a statement, the last in a block expression or a wanna be block
+/// expression like a lamba or match arm.
+fn anchor_stmt(expr: &ast::Expr) -> Option<(&SyntaxNode, bool)> {
+    expr.syntax().ancestors().find_map(|node| {
+        if ast::Stmt::cast(node).is_some() {
+            return Some((node, false));
+        }
+
+        if let Some(expr) = node
+            .parent()
+            .and_then(ast::Block::cast)
+            .and_then(|it| it.expr())
+        {
+            if expr.syntax() == node {
+                return Some((node, false));
+            }
+        }
+
+        if let Some(parent) = node.parent() {
+            if parent.kind() == MATCH_ARM || parent.kind() == LAMBDA_EXPR {
+                return Some((node, true));
+            }
+        }
+
+        None
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_range};
+
+    #[test]
+    fn test_introduce_var_simple() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    foo(<|>1 + 1<|>);
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+    foo(var_name);
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_expr_stmt() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>1 + 1<|>;
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_part_of_expr_stmt() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>1<|> + 1;
+}",
+            "
+fn foo() {
+    let <|>var_name = 1;
+    var_name + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_last_expr() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    bar(<|>1 + 1<|>)
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+    bar(var_name)
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_last_full_expr() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>bar(1 + 1)<|>
+}",
+            "
+fn foo() {
+    let <|>var_name = bar(1 + 1);
+    var_name
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_block_expr_second_to_last() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>{ let x = 0; x }<|>
+    something_else();
+}",
+            "
+fn foo() {
+    let <|>var_name = { let x = 0; x };
+    something_else();
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_in_match_arm_no_block() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => (<|>2 + 2<|>, true)
+        _ => (0, false)
+    };
+}
+",
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => { let <|>var_name = 2 + 2; (var_name, true) }
+        _ => (0, false)
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_in_match_arm_with_block() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => {
+            let y = 1;
+            (<|>2 + y<|>, true)
+        }
+        _ => (0, false)
+    };
+}
+",
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        true => {
+            let y = 1;
+            let <|>var_name = 2 + y;
+            (var_name, true)
+        }
+        _ => (0, false)
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_in_closure_no_block() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn main() {
+    let lambda = |x: u32| <|>x * 2<|>;
+}
+",
+            "
+fn main() {
+    let lambda = |x: u32| { let <|>var_name = x * 2; var_name };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_in_closure_with_block() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn main() {
+    let lambda = |x: u32| { <|>x * 2<|> };
+}
+",
+            "
+fn main() {
+    let lambda = |x: u32| { let <|>var_name = x * 2; var_name };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_path_simple() {
+        check_assist(
+            introduce_variable,
+            "
+fn main() {
+    let o = S<|>ome(true);
+}
+",
+            "
+fn main() {
+    let <|>var_name = Some(true);
+    let o = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_path_method() {
+        check_assist(
+            introduce_variable,
+            "
+fn main() {
+    let v = b<|>ar.foo();
+}
+",
+            "
+fn main() {
+    let <|>var_name = bar.foo();
+    let v = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_return() {
+        check_assist(
+            introduce_variable,
+            "
+fn foo() -> u32 {
+    r<|>eturn 2 + 2;
+}
+",
+            "
+fn foo() -> u32 {
+    let <|>var_name = 2 + 2;
+    return var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_break() {
+        check_assist(
+            introduce_variable,
+            "
+fn main() {
+    let result = loop {
+        b<|>reak 2 + 2;
+    };
+}
+",
+            "
+fn main() {
+    let result = loop {
+        let <|>var_name = 2 + 2;
+        break var_name;
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_for_cast() {
+        check_assist(
+            introduce_variable,
+            "
+fn main() {
+    let v = 0f32 a<|>s u32;
+}
+",
+            "
+fn main() {
+    let <|>var_name = 0f32 as u32;
+    let v = var_name;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_for_return_not_applicable() {
+        check_assist_not_applicable(
+            introduce_variable,
+            "
+fn foo() {
+    r<|>eturn;
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_for_break_not_applicable() {
+        check_assist_not_applicable(
+            introduce_variable,
+            "
+fn main() {
+    loop {
+        b<|>reak;
+    };
+}
+",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_in_comment_not_applicable() {
+        check_assist_not_applicable(
+            introduce_variable,
+            "
+fn main() {
+    let x = true;
+    let tuple = match x {
+        // c<|>omment
+        true => (2 + 2, true)
+        _ => (0, false)
+    };
+}
+",
+        );
+    }
+}