From 9be37b2d3fc0b3852a7f9b134197dec895030201 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 22 May 2022 16:06:36 -0700
Subject: [PATCH] Parse expression after `else` as a condition if followed by
`{`
---
compiler/rustc_parse/src/parser/expr.rs | 62 +++++++++++++++++++++++--
src/test/ui/parser/else-no-if.rs | 32 +++++++++++++
src/test/ui/parser/else-no-if.stderr | 58 +++++++++++++++++++++++
3 files changed, 147 insertions(+), 5 deletions(-)
create mode 100644 src/test/ui/parser/else-no-if.rs
create mode 100644 src/test/ui/parser/else-no-if.stderr
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index b5467c659a205..37e3465694131 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2010,6 +2010,12 @@ impl<'a> Parser<'a> {
Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs))
}
+ /// Parse a block which takes no attributes and has no label
+ fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
+ let blk = self.parse_block()?;
+ Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()))
+ }
+
/// Recover on an explicitly quantified closure expression, e.g., `for<'a> |x: &'a u8| *x + 1`.
fn recover_quantified_closure_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
let lo = self.token.span;
@@ -2157,6 +2163,15 @@ impl<'a> Parser<'a> {
let lo = self.prev_token.span;
let cond = self.parse_cond_expr()?;
+ self.parse_if_after_cond(attrs, lo, cond)
+ }
+
+ fn parse_if_after_cond(
+ &mut self,
+ attrs: AttrVec,
+ lo: Span,
+ cond: P<Expr>,
+ ) -> PResult<'a, P<Expr>> {
let missing_then_block_binop_span = || {
match cond.kind {
ExprKind::Binary(Spanned { span: binop_span, .. }, _, ref right)
@@ -2164,7 +2179,6 @@ impl<'a> Parser<'a> {
_ => None
}
};
-
// Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
// verify that the last statement is either an implicit return (no `;`) or an explicit
// return. This won't catch blocks with an explicit `return`, but that would be caught by
@@ -2256,15 +2270,53 @@ impl<'a> Parser<'a> {
/// Parses an `else { ... }` expression (`else` token already eaten).
fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
- let ctx_span = self.prev_token.span; // `else`
+ let else_span = self.prev_token.span; // `else`
let attrs = self.parse_outer_attributes()?.take_for_recovery(); // For recovery.
let expr = if self.eat_keyword(kw::If) {
self.parse_if_expr(AttrVec::new())?
+ } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
+ self.parse_simple_block()?
} else {
- let blk = self.parse_block()?;
- self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new())
+ let snapshot = self.create_snapshot_for_diagnostic();
+ let first_tok = super::token_descr(&self.token);
+ let first_tok_span = self.token.span;
+ match self.parse_expr() {
+ Ok(cond)
+ // If it's not a free-standing expression, and is followed by a block,
+ // then it's very likely the condition to an `else if`.
+ if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
+ && classify::expr_requires_semi_to_be_stmt(&cond) =>
+ {
+ self.struct_span_err(first_tok_span, format!("expected `{{`, found {first_tok}"))
+ .span_label(else_span, "expected an `if` or a block after this `else`")
+ .span_suggestion(
+ cond.span.shrink_to_lo(),
+ "add an `if` if this is the condition to an chained `if` statement after the `else`",
+ "if ".to_string(),
+ Applicability::MaybeIncorrect,
+ ).multipart_suggestion(
+ "... otherwise, place this expression inside of a block if it is not an `if` condition",
+ vec![
+ (cond.span.shrink_to_lo(), "{ ".to_string()),
+ (cond.span.shrink_to_hi(), " }".to_string()),
+ ],
+ Applicability::MaybeIncorrect,
+ )
+ .emit();
+ self.parse_if_after_cond(AttrVec::new(), cond.span.shrink_to_lo(), cond)?
+ }
+ Err(e) => {
+ e.cancel();
+ self.restore_snapshot(snapshot);
+ self.parse_simple_block()?
+ },
+ Ok(_) => {
+ self.restore_snapshot(snapshot);
+ self.parse_simple_block()?
+ },
+ }
};
- self.error_on_if_block_attrs(ctx_span, true, expr.span, &attrs);
+ self.error_on_if_block_attrs(else_span, true, expr.span, &attrs);
Ok(expr)
}
diff --git a/src/test/ui/parser/else-no-if.rs b/src/test/ui/parser/else-no-if.rs
new file mode 100644
index 0000000000000..f0b40ecde6660
--- /dev/null
+++ b/src/test/ui/parser/else-no-if.rs
@@ -0,0 +1,32 @@
+fn foo() {
+ if true {
+ } else false {
+ //~^ ERROR expected `{`, found keyword `false`
+ }
+}
+
+fn foo2() {
+ if true {
+ } else falsy() {
+ //~^ ERROR expected `{`, found `falsy`
+ }
+}
+
+fn foo3() {
+ if true {
+ } else falsy();
+ //~^ ERROR expected `{`, found `falsy`
+}
+
+fn foo4() {
+ if true {
+ } else loop{}
+ //~^ ERROR expected `{`, found keyword `loop`
+ {}
+}
+
+fn falsy() -> bool {
+ false
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/else-no-if.stderr b/src/test/ui/parser/else-no-if.stderr
new file mode 100644
index 0000000000000..27abbadd7ad24
--- /dev/null
+++ b/src/test/ui/parser/else-no-if.stderr
@@ -0,0 +1,58 @@
+error: expected `{`, found keyword `false`
+ --> $DIR/else-no-if.rs:3:12
+ |
+LL | } else false {
+ | ---- ^^^^^
+ | |
+ | expected an `if` or a block after this `else`
+ |
+help: add an `if` if this is the condition to an chained `if` statement after the `else`
+ |
+LL | } else if false {
+ | ++
+help: ... otherwise, place this expression inside of a block if it is not an `if` condition
+ |
+LL | } else { false } {
+ | + +
+
+error: expected `{`, found `falsy`
+ --> $DIR/else-no-if.rs:10:12
+ |
+LL | } else falsy() {
+ | ---- ^^^^^
+ | |
+ | expected an `if` or a block after this `else`
+ |
+help: add an `if` if this is the condition to an chained `if` statement after the `else`
+ |
+LL | } else if falsy() {
+ | ++
+help: ... otherwise, place this expression inside of a block if it is not an `if` condition
+ |
+LL | } else { falsy() } {
+ | + +
+
+error: expected `{`, found `falsy`
+ --> $DIR/else-no-if.rs:17:12
+ |
+LL | } else falsy();
+ | ^^^^^ expected `{`
+ |
+help: try placing this code inside a block
+ |
+LL | } else { falsy() };
+ | + +
+
+error: expected `{`, found keyword `loop`
+ --> $DIR/else-no-if.rs:23:12
+ |
+LL | } else loop{}
+ | ^^^^ expected `{`
+ |
+help: try placing this code inside a block
+ |
+LL | } else { loop{} }
+ | + +
+
+error: aborting due to 4 previous errors
+