diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs index 4e6641f4c50..fa4df2196a3 100644 --- a/src/libsyntax/ast.rs +++ b/src/libsyntax/ast.rs @@ -844,6 +844,32 @@ pub struct Expr { pub attrs: ThinVec } +impl Expr { + /// Wether this expression would be valid somewhere that expects a value, for example, an `if` + /// condition. + pub fn returns(&self) -> bool { + if let ExprKind::Block(ref block) = self.node { + match block.stmts.last().map(|last_stmt| &last_stmt.node) { + // implicit return + Some(&StmtKind::Expr(_)) => true, + Some(&StmtKind::Semi(ref expr)) => { + if let ExprKind::Ret(_) = expr.node { + // last statement is explicit return + true + } else { + false + } + } + // This is a block that doesn't end in either an implicit or explicit return + _ => false, + } + } else { + // This is not a block, it is a value + true + } + } +} + impl fmt::Debug for Expr { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "expr({}: {})", self.id, pprust::expr_to_string(self)) diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs index 84e3d8ddf70..2b2f925306d 100644 --- a/src/libsyntax/parse/parser.rs +++ b/src/libsyntax/parse/parser.rs @@ -2965,6 +2965,18 @@ impl<'a> Parser<'a> { } let lo = self.prev_span; let cond = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL, 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 + // the dead code lint. + if self.eat_keyword(keywords::Else) || !cond.returns() { + let sp = lo.next_point(); + let mut err = self.diagnostic() + .struct_span_err(sp, "missing condition for `if` statemement"); + err.span_label(sp, "expected if condition here"); + return Err(err) + } let thn = self.parse_block()?; let mut els: Option> = None; let mut hi = thn.span; diff --git a/src/test/ui/issue-13483.rs b/src/test/ui/issue-13483.rs new file mode 100644 index 00000000000..86378043912 --- /dev/null +++ b/src/test/ui/issue-13483.rs @@ -0,0 +1,25 @@ +// Copyright 2017 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +fn main() { + if true { + } else if { + } else { + } +} + +fn foo() { + if true { + } else if { + } + bar(); +} + +fn bar() {} diff --git a/src/test/ui/issue-13483.stderr b/src/test/ui/issue-13483.stderr new file mode 100644 index 00000000000..3446969dfd2 --- /dev/null +++ b/src/test/ui/issue-13483.stderr @@ -0,0 +1,14 @@ +error: missing condition for `if` statemement + --> $DIR/issue-13483.rs:13:14 + | +13 | } else if { + | ^ expected if condition here + +error: missing condition for `if` statemement + --> $DIR/issue-13483.rs:20:14 + | +20 | } else if { + | ^ expected if condition here + +error: aborting due to 2 previous errors +