rust-analyzer/crates/ide-diagnostics/src/handlers/remove_unnecessary_else.rs

use hir::{db::ExpandDatabase, diagnostics::RemoveUnnecessaryElse, HirFileIdExt};
use ide_db::{assists::Assist, source_change::SourceChange};
use itertools::Itertools;
use syntax::{
    ast::{
        self,
        edit::{AstNodeEdit, IndentLevel},
    },
    AstNode, SyntaxToken, TextRange,
};
use text_edit::TextEdit;

use crate::{
    adjusted_display_range, fix, Diagnostic, DiagnosticCode, DiagnosticsContext, Severity,
};

// Diagnostic: remove-unnecessary-else
//
// This diagnostic is triggered when there is an `else` block for an `if` expression whose
// then branch diverges (e.g. ends with a `return`, `continue`, `break` e.t.c).
pub(crate) fn remove_unnecessary_else(
    ctx: &DiagnosticsContext<'_>,
    d: &RemoveUnnecessaryElse,
) -> Option<Diagnostic> {
    if d.if_expr.file_id.macro_file().is_some() {
        // FIXME: Our infra can't handle allow from within macro expansions rn
        return None;
    }

    let display_range = adjusted_display_range(ctx, d.if_expr, &|if_expr| {
        if_expr.else_token().as_ref().map(SyntaxToken::text_range)
    });
    Some(
        Diagnostic::new(
            DiagnosticCode::Ra("remove-unnecessary-else", Severity::WeakWarning),
            "remove unnecessary else block",
            display_range,
        )
        .experimental()
        .with_fixes(fixes(ctx, d)),
    )
}

fn fixes(ctx: &DiagnosticsContext<'_>, d: &RemoveUnnecessaryElse) -> Option<Vec<Assist>> {
    let root = ctx.sema.db.parse_or_expand(d.if_expr.file_id);
    let if_expr = d.if_expr.value.to_node(&root);
    let if_expr = ctx.sema.original_ast_node(if_expr)?;

    let mut indent = IndentLevel::from_node(if_expr.syntax());
    let has_parent_if_expr = if_expr.syntax().parent().and_then(ast::IfExpr::cast).is_some();
    if has_parent_if_expr {
        indent = indent + 1;
    }
    let else_replacement = match if_expr.else_branch()? {
        ast::ElseBranch::Block(block) => block
            .statements()
            .map(|stmt| format!("\n{indent}{stmt}"))
            .chain(block.tail_expr().map(|tail| format!("\n{indent}{tail}")))
            .join(""),
        ast::ElseBranch::IfExpr(mut nested_if_expr) => {
            if has_parent_if_expr {
                nested_if_expr = nested_if_expr.indent(IndentLevel(1))
            }
            format!("\n{indent}{nested_if_expr}")
        }
    };
    let (replacement, range) = if has_parent_if_expr {
        let base_indent = IndentLevel::from_node(if_expr.syntax());
        let then_indent = base_indent + 1;
        let then_child_indent = then_indent + 1;

        let condition = if_expr.condition()?;
        let then_stmts = if_expr
            .then_branch()?
            .statements()
            .map(|stmt| format!("\n{then_child_indent}{stmt}"))
            .join("");
        let then_replacement =
            format!("\n{then_indent}if {condition} {{{then_stmts}\n{then_indent}}}",);
        let replacement = format!("{{{then_replacement}{else_replacement}\n{base_indent}}}");
        (replacement, if_expr.syntax().text_range())
    } else {
        (
            else_replacement,
            TextRange::new(
                if_expr.then_branch()?.syntax().text_range().end(),
                if_expr.syntax().text_range().end(),
            ),
        )
    };

    let edit = TextEdit::replace(range, replacement);
    let source_change =
        SourceChange::from_text_edit(d.if_expr.file_id.original_file(ctx.sema.db), edit);

    Some(vec![fix(
        "remove_unnecessary_else",
        "Remove unnecessary else block",
        source_change,
        range,
    )])
}

#[cfg(test)]
mod tests {
    use crate::tests::{check_diagnostics_with_disabled, check_fix};

    #[test]
    fn remove_unnecessary_else_for_return() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        return bar;
    } else {
    //^^^^ 💡 weak: remove unnecessary else block
        do_something_else();
    }
}
"#,
            &["needless_return", "E0425"],
        );
        check_fix(
            r#"
fn test() {
    if foo {
        return bar;
    } else$0 {
        do_something_else();
    }
}
"#,
            r#"
fn test() {
    if foo {
        return bar;
    }
    do_something_else();
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_return2() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        return bar;
    } else if qux {
    //^^^^ 💡 weak: remove unnecessary else block
        do_something_else();
    } else {
        do_something_else2();
    }
}
"#,
            &["needless_return", "E0425"],
        );
        check_fix(
            r#"
fn test() {
    if foo {
        return bar;
    } else$0 if qux {
        do_something_else();
    } else {
        do_something_else2();
    }
}
"#,
            r#"
fn test() {
    if foo {
        return bar;
    }
    if qux {
        do_something_else();
    } else {
        do_something_else2();
    }
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_return3() {
        check_diagnostics_with_disabled(
            r#"
fn test(a: bool) -> i32 {
    if a {
        return 1;
    } else {
    //^^^^ 💡 weak: remove unnecessary else block
        0
    }
}
"#,
            &["needless_return", "E0425"],
        );
        check_fix(
            r#"
fn test(a: bool) -> i32 {
    if a {
        return 1;
    } else$0 {
        0
    }
}
"#,
            r#"
fn test(a: bool) -> i32 {
    if a {
        return 1;
    }
    0
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_return_in_child_if_expr() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        do_something();
    } else if qux {
        return bar;
    } else {
    //^^^^ 💡 weak: remove unnecessary else block
        do_something_else();
    }
}
"#,
            &["needless_return", "E0425"],
        );
        check_fix(
            r#"
fn test() {
    if foo {
        do_something();
    } else if qux {
        return bar;
    } else$0 {
        do_something_else();
    }
}
"#,
            r#"
fn test() {
    if foo {
        do_something();
    } else {
        if qux {
            return bar;
        }
        do_something_else();
    }
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_return_in_child_if_expr2() {
        check_fix(
            r#"
fn test() {
    if foo {
        do_something();
    } else if qux {
        return bar;
    } else$0 if quux {
        do_something_else();
    } else {
        do_something_else2();
    }
}
"#,
            r#"
fn test() {
    if foo {
        do_something();
    } else {
        if qux {
            return bar;
        }
        if quux {
            do_something_else();
        } else {
            do_something_else2();
        }
    }
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_break() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    loop {
        if foo {
            break;
        } else {
        //^^^^ 💡 weak: remove unnecessary else block
            do_something_else();
        }
    }
}
"#,
            &["E0425"],
        );
        check_fix(
            r#"
fn test() {
    loop {
        if foo {
            break;
        } else$0 {
            do_something_else();
        }
    }
}
"#,
            r#"
fn test() {
    loop {
        if foo {
            break;
        }
        do_something_else();
    }
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_continue() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    loop {
        if foo {
            continue;
        } else {
        //^^^^ 💡 weak: remove unnecessary else block
            do_something_else();
        }
    }
}
"#,
            &["E0425"],
        );
        check_fix(
            r#"
fn test() {
    loop {
        if foo {
            continue;
        } else$0 {
            do_something_else();
        }
    }
}
"#,
            r#"
fn test() {
    loop {
        if foo {
            continue;
        }
        do_something_else();
    }
}
"#,
        );
    }

    #[test]
    fn remove_unnecessary_else_for_never() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        never();
    } else {
    //^^^^ 💡 weak: remove unnecessary else block
        do_something_else();
    }
}

fn never() -> ! {
    loop {}
}
"#,
            &["E0425"],
        );
        check_fix(
            r#"
fn test() {
    if foo {
        never();
    } else$0 {
        do_something_else();
    }
}

fn never() -> ! {
    loop {}
}
"#,
            r#"
fn test() {
    if foo {
        never();
    }
    do_something_else();
}

fn never() -> ! {
    loop {}
}
"#,
        );
    }

    #[test]
    fn no_diagnostic_if_no_else_branch() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        return bar;
    }

    do_something_else();
}
"#,
            &["E0425"],
        );
    }

    #[test]
    fn no_diagnostic_if_no_divergence() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        do_something();
    } else {
        do_something_else();
    }
}
"#,
            &["E0425"],
        );
    }

    #[test]
    fn no_diagnostic_if_no_divergence_in_else_branch() {
        check_diagnostics_with_disabled(
            r#"
fn test() {
    if foo {
        do_something();
    } else {
        return bar;
    }
}
"#,
            &["needless_return", "E0425"],
        );
    }

    #[test]
    fn no_diagnostic_if_not_expr_stmt() {
        check_diagnostics_with_disabled(
            r#"
fn test1() {
    let _x = if a {
        return;
    } else {
        1
    };
}

fn test2() {
    let _x = if a {
        return;
    } else if b {
        return;
    } else if c {
        1
    } else {
        return;
    };
}
"#,
            &["needless_return", "E0425"],
        );
        check_diagnostics_with_disabled(
            r#"
fn test3() -> u8 {
    foo(if a { return 1 } else { 0 })
}
"#,
            &["E0425"],
        );
    }
}