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convert_match_to_let_else.rs
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convert_match_to_let_else.rs
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use ide_db::defs::{Definition, NameRefClass};
use syntax::{
ast::{self, HasName, Name},
ted, AstNode, SyntaxNode,
};
use crate::{
assist_context::{AssistContext, Assists},
AssistId, AssistKind,
};
// Assist: convert_match_to_let_else
//
// Converts let statement with match initializer to let-else statement.
//
// ```
// # //- minicore: option
// fn foo(opt: Option<()>) {
// let val$0 = match opt {
// Some(it) => it,
// None => return,
// };
// }
// ```
// ->
// ```
// fn foo(opt: Option<()>) {
// let Some(val) = opt else { return };
// }
// ```
pub(crate) fn convert_match_to_let_else(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
let let_stmt: ast::LetStmt = ctx.find_node_at_offset()?;
let pat = let_stmt.pat()?;
if ctx.offset() > pat.syntax().text_range().end() {
return None;
}
let Some(ast::Expr::MatchExpr(initializer)) = let_stmt.initializer() else { return None };
let initializer_expr = initializer.expr()?;
let (extracting_arm, diverging_arm) = find_arms(ctx, &initializer)?;
if extracting_arm.guard().is_some() {
cov_mark::hit!(extracting_arm_has_guard);
return None;
}
let diverging_arm_expr = match diverging_arm.expr()? {
ast::Expr::BlockExpr(block) if block.modifier().is_none() && block.label().is_none() => {
block.to_string()
}
other => format!("{{ {other} }}"),
};
let extracting_arm_pat = extracting_arm.pat()?;
let extracted_variable_positions = find_extracted_variable(ctx, &extracting_arm)?;
acc.add(
AssistId("convert_match_to_let_else", AssistKind::RefactorRewrite),
"Convert match to let-else",
let_stmt.syntax().text_range(),
|builder| {
let extracting_arm_pat =
rename_variable(&extracting_arm_pat, &extracted_variable_positions, pat);
builder.replace(
let_stmt.syntax().text_range(),
format!("let {extracting_arm_pat} = {initializer_expr} else {diverging_arm_expr};"),
)
},
)
}
// Given a match expression, find extracting and diverging arms.
fn find_arms(
ctx: &AssistContext<'_>,
match_expr: &ast::MatchExpr,
) -> Option<(ast::MatchArm, ast::MatchArm)> {
let arms = match_expr.match_arm_list()?.arms().collect::<Vec<_>>();
if arms.len() != 2 {
return None;
}
let mut extracting = None;
let mut diverging = None;
for arm in arms {
if ctx.sema.type_of_expr(&arm.expr()?)?.original().is_never() {
diverging = Some(arm);
} else {
extracting = Some(arm);
}
}
match (extracting, diverging) {
(Some(extracting), Some(diverging)) => Some((extracting, diverging)),
_ => {
cov_mark::hit!(non_diverging_match);
None
}
}
}
// Given an extracting arm, find the extracted variable.
fn find_extracted_variable(ctx: &AssistContext<'_>, arm: &ast::MatchArm) -> Option<Vec<Name>> {
match arm.expr()? {
ast::Expr::PathExpr(path) => {
let name_ref = path.syntax().descendants().find_map(ast::NameRef::cast)?;
match NameRefClass::classify(&ctx.sema, &name_ref)? {
NameRefClass::Definition(Definition::Local(local)) => {
let source =
local.sources(ctx.db()).into_iter().map(|x| x.into_ident_pat()?.name());
source.collect()
}
_ => None,
}
}
_ => {
cov_mark::hit!(extracting_arm_is_not_an_identity_expr);
None
}
}
}
// Rename `extracted` with `binding` in `pat`.
fn rename_variable(pat: &ast::Pat, extracted: &[Name], binding: ast::Pat) -> SyntaxNode {
let syntax = pat.syntax().clone_for_update();
let extracted = extracted
.iter()
.map(|e| syntax.covering_element(e.syntax().text_range()))
.collect::<Vec<_>>();
for extracted_syntax in extracted {
// If `extracted` variable is a record field, we should rename it to `binding`,
// otherwise we just need to replace `extracted` with `binding`.
if let Some(record_pat_field) =
extracted_syntax.ancestors().find_map(ast::RecordPatField::cast)
{
if let Some(name_ref) = record_pat_field.field_name() {
ted::replace(
record_pat_field.syntax(),
ast::make::record_pat_field(
ast::make::name_ref(&name_ref.text()),
binding.clone(),
)
.syntax()
.clone_for_update(),
);
}
} else {
ted::replace(extracted_syntax, binding.clone().syntax().clone_for_update());
}
}
syntax
}
#[cfg(test)]
mod tests {
use crate::tests::{check_assist, check_assist_not_applicable};
use super::*;
#[test]
fn should_not_be_applicable_for_non_diverging_match() {
cov_mark::check!(non_diverging_match);
check_assist_not_applicable(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
let val$0 = match opt {
Some(it) => it,
None => (),
};
}
"#,
);
}
#[test]
fn or_pattern_multiple_binding() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
enum Foo {
A(u32),
B(u32),
C(String),
}
fn foo(opt: Option<Foo>) -> Result<u32, ()> {
let va$0lue = match opt {
Some(Foo::A(it) | Foo::B(it)) => it,
_ => return Err(()),
};
}
"#,
r#"
enum Foo {
A(u32),
B(u32),
C(String),
}
fn foo(opt: Option<Foo>) -> Result<u32, ()> {
let Some(Foo::A(value) | Foo::B(value)) = opt else { return Err(()) };
}
"#,
);
}
#[test]
fn should_not_be_applicable_if_extracting_arm_is_not_an_identity_expr() {
cov_mark::check_count!(extracting_arm_is_not_an_identity_expr, 2);
check_assist_not_applicable(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<i32>) {
let val$0 = match opt {
Some(it) => it + 1,
None => return,
};
}
"#,
);
check_assist_not_applicable(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
let val$0 = match opt {
Some(it) => {
let _ = 1 + 1;
it
},
None => return,
};
}
"#,
);
}
#[test]
fn should_not_be_applicable_if_extracting_arm_has_guard() {
cov_mark::check!(extracting_arm_has_guard);
check_assist_not_applicable(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
let val$0 = match opt {
Some(it) if 2 > 1 => it,
None => return,
};
}
"#,
);
}
#[test]
fn basic_pattern() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
let val$0 = match opt {
Some(it) => it,
None => return,
};
}
"#,
r#"
fn foo(opt: Option<()>) {
let Some(val) = opt else { return };
}
"#,
);
}
#[test]
fn keeps_modifiers() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
let ref mut val$0 = match opt {
Some(it) => it,
None => return,
};
}
"#,
r#"
fn foo(opt: Option<()>) {
let Some(ref mut val) = opt else { return };
}
"#,
);
}
#[test]
fn nested_pattern() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option, result
fn foo(opt: Option<Result<()>>) {
let val$0 = match opt {
Some(Ok(it)) => it,
_ => return,
};
}
"#,
r#"
fn foo(opt: Option<Result<()>>) {
let Some(Ok(val)) = opt else { return };
}
"#,
);
}
#[test]
fn works_with_any_diverging_block() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
loop {
let val$0 = match opt {
Some(it) => it,
None => break,
};
}
}
"#,
r#"
fn foo(opt: Option<()>) {
loop {
let Some(val) = opt else { break };
}
}
"#,
);
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<()>) {
loop {
let val$0 = match opt {
Some(it) => it,
None => continue,
};
}
}
"#,
r#"
fn foo(opt: Option<()>) {
loop {
let Some(val) = opt else { continue };
}
}
"#,
);
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn panic() -> ! {}
fn foo(opt: Option<()>) {
loop {
let val$0 = match opt {
Some(it) => it,
None => panic(),
};
}
}
"#,
r#"
fn panic() -> ! {}
fn foo(opt: Option<()>) {
loop {
let Some(val) = opt else { panic() };
}
}
"#,
);
}
#[test]
fn struct_pattern() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
struct Point {
x: i32,
y: i32,
}
fn foo(opt: Option<Point>) {
let val$0 = match opt {
Some(Point { x: 0, y }) => y,
_ => return,
};
}
"#,
r#"
struct Point {
x: i32,
y: i32,
}
fn foo(opt: Option<Point>) {
let Some(Point { x: 0, y: val }) = opt else { return };
}
"#,
);
}
#[test]
fn renames_whole_binding() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn foo(opt: Option<i32>) -> Option<i32> {
let val$0 = match opt {
it @ Some(42) => it,
_ => return None,
};
val
}
"#,
r#"
fn foo(opt: Option<i32>) -> Option<i32> {
let val @ Some(42) = opt else { return None };
val
}
"#,
);
}
#[test]
fn complex_pattern() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn f() {
let (x, y)$0 = match Some((0, 1)) {
Some(it) => it,
None => return,
};
}
"#,
r#"
fn f() {
let Some((x, y)) = Some((0, 1)) else { return };
}
"#,
);
}
#[test]
fn diverging_block() {
check_assist(
convert_match_to_let_else,
r#"
//- minicore: option
fn f() {
let x$0 = match Some(()) {
Some(it) => it,
None => {//comment
println!("nope");
return
},
};
}
"#,
r#"
fn f() {
let Some(x) = Some(()) else {//comment
println!("nope");
return
};
}
"#,
);
}
}