Rollup merge of #47247 - estebank:suggest-cast, r=petrochenkov

Suggest casting on numeric type error

Re #47168.

src/librustc/hir/mod.rs

@@ -34,13 +34,14 @@
 use syntax_pos::{Span, DUMMY_SP};
 use syntax::codemap::{self, Spanned};
 use syntax::abi::Abi;
-use syntax::ast::{Ident, Name, NodeId, DUMMY_NODE_ID, AsmDialect};
+use syntax::ast::{self, Ident, Name, NodeId, DUMMY_NODE_ID, AsmDialect};
 use syntax::ast::{Attribute, Lit, StrStyle, FloatTy, IntTy, UintTy, MetaItem};
 use syntax::ext::hygiene::SyntaxContext;
 use syntax::ptr::P;
 use syntax::symbol::{Symbol, keywords};
 use syntax::tokenstream::TokenStream;
 use syntax::util::ThinVec;
+use syntax::util::parser::ExprPrecedence;
 use ty::AdtKind;
 
 use rustc_data_structures::indexed_vec;
@@ -958,6 +959,31 @@ pub fn is_by_value(self) -> bool {
     }
 }
 
+impl Into<ast::BinOpKind> for BinOp_ {
+    fn into(self) -> ast::BinOpKind {
+        match self {
+            BiAdd => ast::BinOpKind::Add,
+            BiSub => ast::BinOpKind::Sub,
+            BiMul => ast::BinOpKind::Mul,
+            BiDiv => ast::BinOpKind::Div,
+            BiRem => ast::BinOpKind::Rem,
+            BiAnd => ast::BinOpKind::And,
+            BiOr => ast::BinOpKind::Or,
+            BiBitXor => ast::BinOpKind::BitXor,
+            BiBitAnd => ast::BinOpKind::BitAnd,
+            BiBitOr => ast::BinOpKind::BitOr,
+            BiShl => ast::BinOpKind::Shl,
+            BiShr => ast::BinOpKind::Shr,
+            BiEq => ast::BinOpKind::Eq,
+            BiLt => ast::BinOpKind::Lt,
+            BiLe => ast::BinOpKind::Le,
+            BiNe => ast::BinOpKind::Ne,
+            BiGe => ast::BinOpKind::Ge,
+            BiGt => ast::BinOpKind::Gt,
+        }
+    }
+}
+
 pub type BinOp = Spanned<BinOp_>;
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
@@ -1166,6 +1192,42 @@ pub struct Expr {
     pub hir_id: HirId,
 }
 
+impl Expr {
+    pub fn precedence(&self) -> ExprPrecedence {
+        match self.node {
+            ExprBox(_) => ExprPrecedence::Box,
+            ExprArray(_) => ExprPrecedence::Array,
+            ExprCall(..) => ExprPrecedence::Call,
+            ExprMethodCall(..) => ExprPrecedence::MethodCall,
+            ExprTup(_) => ExprPrecedence::Tup,
+            ExprBinary(op, ..) => ExprPrecedence::Binary(op.node.into()),
+            ExprUnary(..) => ExprPrecedence::Unary,
+            ExprLit(_) => ExprPrecedence::Lit,
+            ExprType(..) | ExprCast(..) => ExprPrecedence::Cast,
+            ExprIf(..) => ExprPrecedence::If,
+            ExprWhile(..) => ExprPrecedence::While,
+            ExprLoop(..) => ExprPrecedence::Loop,
+            ExprMatch(..) => ExprPrecedence::Match,
+            ExprClosure(..) => ExprPrecedence::Closure,
+            ExprBlock(..) => ExprPrecedence::Block,
+            ExprAssign(..) => ExprPrecedence::Assign,
+            ExprAssignOp(..) => ExprPrecedence::AssignOp,
+            ExprField(..) => ExprPrecedence::Field,
+            ExprTupField(..) => ExprPrecedence::TupField,
+            ExprIndex(..) => ExprPrecedence::Index,
+            ExprPath(..) => ExprPrecedence::Path,
+            ExprAddrOf(..) => ExprPrecedence::AddrOf,
+            ExprBreak(..) => ExprPrecedence::Break,
+            ExprAgain(..) => ExprPrecedence::Continue,
+            ExprRet(..) => ExprPrecedence::Ret,
+            ExprInlineAsm(..) => ExprPrecedence::InlineAsm,
+            ExprStruct(..) => ExprPrecedence::Struct,
+            ExprRepeat(..) => ExprPrecedence::Repeat,
+            ExprYield(..) => ExprPrecedence::Yield,
+        }
+    }
+}
+
 impl fmt::Debug for Expr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "expr({}: {})", self.id,

src/librustc/hir/print.rs

@@ -1104,7 +1104,7 @@ fn print_call_post(&mut self, args: &[hir::Expr]) -> io::Result<()> {
     }
 
     pub fn print_expr_maybe_paren(&mut self, expr: &hir::Expr, prec: i8) -> io::Result<()> {
-        let needs_par = expr_precedence(expr) < prec;
+        let needs_par = expr.precedence().order() < prec;
         if needs_par {
             self.popen()?;
         }
@@ -2318,55 +2318,6 @@ fn stmt_ends_with_semi(stmt: &hir::Stmt_) -> bool {
     }
 }
 
-
-fn expr_precedence(expr: &hir::Expr) -> i8 {
-    use syntax::util::parser::*;
-
-    match expr.node {
-        hir::ExprClosure(..) => PREC_CLOSURE,
-
-        hir::ExprBreak(..) |
-        hir::ExprAgain(..) |
-        hir::ExprRet(..) |
-        hir::ExprYield(..) => PREC_JUMP,
-
-        // Binop-like expr kinds, handled by `AssocOp`.
-        hir::ExprBinary(op, _, _) => bin_op_to_assoc_op(op.node).precedence() as i8,
-
-        hir::ExprCast(..) => AssocOp::As.precedence() as i8,
-        hir::ExprType(..) => AssocOp::Colon.precedence() as i8,
-
-        hir::ExprAssign(..) |
-        hir::ExprAssignOp(..) => AssocOp::Assign.precedence() as i8,
-
-        // Unary, prefix
-        hir::ExprBox(..) |
-        hir::ExprAddrOf(..) |
-        hir::ExprUnary(..) => PREC_PREFIX,
-
-        // Unary, postfix
-        hir::ExprCall(..) |
-        hir::ExprMethodCall(..) |
-        hir::ExprField(..) |
-        hir::ExprTupField(..) |
-        hir::ExprIndex(..) |
-        hir::ExprInlineAsm(..) => PREC_POSTFIX,
-
-        // Never need parens
-        hir::ExprArray(..) |
-        hir::ExprRepeat(..) |
-        hir::ExprTup(..) |
-        hir::ExprLit(..) |
-        hir::ExprPath(..) |
-        hir::ExprIf(..) |
-        hir::ExprWhile(..) |
-        hir::ExprLoop(..) |
-        hir::ExprMatch(..) |
-        hir::ExprBlock(..) |
-        hir::ExprStruct(..) => PREC_PAREN,
-    }
-}
-
 fn bin_op_to_assoc_op(op: hir::BinOp_) -> AssocOp {
     use hir::BinOp_::*;
     match op {

src/librustc_typeck/check/demand.rs

@@ -15,6 +15,7 @@
 use rustc::traits::ObligationCause;
 
 use syntax::ast;
+use syntax::util::parser::AssocOp;
 use syntax_pos::{self, Span};
 use rustc::hir;
 use rustc::hir::print;
@@ -137,7 +138,7 @@ pub fn demand_coerce_diag(&self,
 
         if let Some((msg, suggestion)) = self.check_ref(expr, checked_ty, expected) {
             err.span_suggestion(expr.span, msg, suggestion);
-        } else {
+        } else if !self.check_for_cast(&mut err, expr, expr_ty, expected) {
             let methods = self.get_conversion_methods(expected, checked_ty);
             if let Ok(expr_text) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
                 let suggestions = iter::repeat(expr_text).zip(methods.iter())
@@ -287,8 +288,7 @@ fn check_ref(&self,
                         // Maybe remove `&`?
                         hir::ExprAddrOf(_, ref expr) => {
                             if let Ok(code) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
-                                return Some(("consider removing the borrow",
-                                             code));
+                                return Some(("consider removing the borrow", code));
                             }
                         }
 
@@ -303,7 +303,7 @@ fn check_ref(&self,
                                                  format!("*{}", code)));
                                 }
                             }
-                        },
+                        }
                     }
                 }
                 None
@@ -311,4 +311,240 @@ fn check_ref(&self,
             _ => None,
         }
     }
+
+    fn check_for_cast(&self,
+                      err: &mut DiagnosticBuilder<'tcx>,
+                      expr: &hir::Expr,
+                      checked_ty: Ty<'tcx>,
+                      expected_ty: Ty<'tcx>)
+                      -> bool {
+        let will_truncate = "will truncate the source value";
+        let depending_on_isize = "will truncate or zero-extend depending on the bit width of \
+                                  `isize`";
+        let depending_on_usize = "will truncate or zero-extend depending on the bit width of \
+                                  `usize`";
+        let will_sign_extend = "will sign-extend the source value";
+        let will_zero_extend = "will zero-extend the source value";
+
+        // If casting this expression to a given numeric type would be appropriate in case of a type
+        // mismatch.
+        //
+        // We want to minimize the amount of casting operations that are suggested, as it can be a
+        // lossy operation with potentially bad side effects, so we only suggest when encountering
+        // an expression that indicates that the original type couldn't be directly changed.
+        //
+        // For now, don't suggest casting with `as`.
+        let can_cast = false;
+
+        let needs_paren = expr.precedence().order() < (AssocOp::As.precedence() as i8);
+
+        if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
+            let msg = format!("you can cast an `{}` to `{}`", checked_ty, expected_ty);
+            let cast_suggestion = format!("{}{}{} as {}",
+                                          if needs_paren { "(" } else { "" },
+                                          src,
+                                          if needs_paren { ")" } else { "" },
+                                          expected_ty);
+            let into_suggestion = format!("{}{}{}.into()",
+                                          if needs_paren { "(" } else { "" },
+                                          src,
+                                          if needs_paren { ")" } else { "" });
+
+            match (&expected_ty.sty, &checked_ty.sty) {
+                (&ty::TyInt(ref exp), &ty::TyInt(ref found)) => {
+                    match (found.bit_width(), exp.bit_width()) {
+                        (Some(found), Some(exp)) if found > exp => {
+                            if can_cast {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_truncate),
+                                                    cast_suggestion);
+                            }
+                        }
+                        (None, _) | (_, None) => {
+                            if can_cast {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_isize),
+                                                    cast_suggestion);
+                            }
+                        }
+                        _ => {
+                            err.span_suggestion(expr.span,
+                                                &format!("{}, which {}", msg, will_sign_extend),
+                                                into_suggestion);
+                        }
+                    }
+                    true
+                }
+                (&ty::TyUint(ref exp), &ty::TyUint(ref found)) => {
+                    match (found.bit_width(), exp.bit_width()) {
+                        (Some(found), Some(exp)) if found > exp => {
+                            if can_cast {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_truncate),
+                                                    cast_suggestion);
+                            }
+                        }
+                        (None, _) | (_, None) => {
+                            if can_cast {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_usize),
+                                                    cast_suggestion);
+                            }
+                        }
+                        _ => {
+                            err.span_suggestion(expr.span,
+                                                &format!("{}, which {}", msg, will_zero_extend),
+                                                into_suggestion);
+                        }
+                    }
+                    true
+                }
+                (&ty::TyInt(ref exp), &ty::TyUint(ref found)) => {
+                    if can_cast {
+                        match (found.bit_width(), exp.bit_width()) {
+                            (Some(found), Some(exp)) if found > exp - 1 => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_truncate),
+                                                    cast_suggestion);
+                            }
+                            (None, None) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_truncate),
+                                                    cast_suggestion);
+                            }
+                            (None, _) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_isize),
+                                                    cast_suggestion);
+                            }
+                            (_, None) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_usize),
+                                                    cast_suggestion);
+                            }
+                            _ => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_zero_extend),
+                                                    cast_suggestion);
+                            }
+                        }
+                    }
+                    true
+                }
+                (&ty::TyUint(ref exp), &ty::TyInt(ref found)) => {
+                    if can_cast {
+                        match (found.bit_width(), exp.bit_width()) {
+                            (Some(found), Some(exp)) if found - 1 > exp => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_truncate),
+                                                    cast_suggestion);
+                            }
+                            (None, None) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_sign_extend),
+                                                    cast_suggestion);
+                            }
+                            (None, _) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_usize),
+                                                    cast_suggestion);
+                            }
+                            (_, None) => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}",
+                                                             msg,
+                                                             depending_on_isize),
+                                                    cast_suggestion);
+                            }
+                            _ => {
+                                err.span_suggestion(expr.span,
+                                                    &format!("{}, which {}", msg, will_sign_extend),
+                                                    cast_suggestion);
+                            }
+                        }
+                    }
+                    true
+                }
+                (&ty::TyFloat(ref exp), &ty::TyFloat(ref found)) => {
+                    if found.bit_width() < exp.bit_width() {
+                        err.span_suggestion(expr.span,
+                                            &format!("{} in a lossless way",
+                                                     msg),
+                                            into_suggestion);
+                    } else if can_cast {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, producing the closest possible value",
+                                                     msg),
+                                            cast_suggestion);
+                        err.warn("casting here will cause undefined behavior if the value is \
+                                  finite but larger or smaller than the largest or smallest \
+                                  finite value representable by `f32` (this is a bug and will be \
+                                  fixed)");
+                    }
+                    true
+                }
+                (&ty::TyUint(_), &ty::TyFloat(_)) | (&ty::TyInt(_), &ty::TyFloat(_)) => {
+                    if can_cast {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, rounding the float towards zero",
+                                                     msg),
+                                            cast_suggestion);
+                        err.warn("casting here will cause undefined behavior if the rounded value \
+                                  cannot be represented by the target integer type, including \
+                                  `Inf` and `NaN` (this is a bug and will be fixed)");
+                    }
+                    true
+                }
+                (&ty::TyFloat(ref exp), &ty::TyUint(ref found)) => {
+                    // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
+                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, producing the floating point \
+                                                      representation of the integer",
+                                                      msg),
+                                            into_suggestion);
+                    } else if can_cast {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, producing the floating point \
+                                                      representation of the integer, rounded if \
+                                                      necessary",
+                                                      msg),
+                                            cast_suggestion);
+                    }
+                    true
+                }
+                (&ty::TyFloat(ref exp), &ty::TyInt(ref found)) => {
+                    // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
+                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, producing the floating point \
+                                                      representation of the integer",
+                                                      msg),
+                                            into_suggestion);
+                    } else if can_cast {
+                        err.span_suggestion(expr.span,
+                                            &format!("{}, producing the floating point \
+                                                      representation of the integer, rounded if \
+                                                      necessary",
+                                                      msg),
+                                            cast_suggestion);
+                    }
+                    true
+                }
+                _ => false,
+            }
+        } else {
+            false
+        }
+    }
 }

src/libsyntax/ast.rs

@@ -15,6 +15,7 @@
 pub use self::PathParameters::*;
 pub use symbol::{Ident, Symbol as Name};
 pub use util::ThinVec;
+pub use util::parser::ExprPrecedence;
 
 use syntax_pos::{Span, DUMMY_SP};
 use codemap::{respan, Spanned};
@@ -730,6 +731,7 @@ pub fn is_shift(&self) -> bool {
             _ => false
         }
     }
+
     pub fn is_comparison(&self) -> bool {
         use self::BinOpKind::*;
         match *self {
@@ -740,6 +742,7 @@ pub fn is_comparison(&self) -> bool {
             false,
         }
     }
+
     /// Returns `true` if the binary operator takes its arguments by value
     pub fn is_by_value(&self) -> bool {
         !self.is_comparison()
@@ -966,6 +969,49 @@ pub(super) fn to_ty(&self) -> Option<P<Ty>> {
 
         Some(P(Ty { node, id: self.id, span: self.span }))
     }
+
+    pub fn precedence(&self) -> ExprPrecedence {
+        match self.node {
+            ExprKind::Box(_) => ExprPrecedence::Box,
+            ExprKind::InPlace(..) => ExprPrecedence::InPlace,
+            ExprKind::Array(_) => ExprPrecedence::Array,
+            ExprKind::Call(..) => ExprPrecedence::Call,
+            ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
+            ExprKind::Tup(_) => ExprPrecedence::Tup,
+            ExprKind::Binary(op, ..) => ExprPrecedence::Binary(op.node),
+            ExprKind::Unary(..) => ExprPrecedence::Unary,
+            ExprKind::Lit(_) => ExprPrecedence::Lit,
+            ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
+            ExprKind::If(..) => ExprPrecedence::If,
+            ExprKind::IfLet(..) => ExprPrecedence::IfLet,
+            ExprKind::While(..) => ExprPrecedence::While,
+            ExprKind::WhileLet(..) => ExprPrecedence::WhileLet,
+            ExprKind::ForLoop(..) => ExprPrecedence::ForLoop,
+            ExprKind::Loop(..) => ExprPrecedence::Loop,
+            ExprKind::Match(..) => ExprPrecedence::Match,
+            ExprKind::Closure(..) => ExprPrecedence::Closure,
+            ExprKind::Block(..) => ExprPrecedence::Block,
+            ExprKind::Catch(..) => ExprPrecedence::Catch,
+            ExprKind::Assign(..) => ExprPrecedence::Assign,
+            ExprKind::AssignOp(..) => ExprPrecedence::AssignOp,
+            ExprKind::Field(..) => ExprPrecedence::Field,
+            ExprKind::TupField(..) => ExprPrecedence::TupField,
+            ExprKind::Index(..) => ExprPrecedence::Index,
+            ExprKind::Range(..) => ExprPrecedence::Range,
+            ExprKind::Path(..) => ExprPrecedence::Path,
+            ExprKind::AddrOf(..) => ExprPrecedence::AddrOf,
+            ExprKind::Break(..) => ExprPrecedence::Break,
+            ExprKind::Continue(..) => ExprPrecedence::Continue,
+            ExprKind::Ret(..) => ExprPrecedence::Ret,
+            ExprKind::InlineAsm(..) => ExprPrecedence::InlineAsm,
+            ExprKind::Mac(..) => ExprPrecedence::Mac,
+            ExprKind::Struct(..) => ExprPrecedence::Struct,
+            ExprKind::Repeat(..) => ExprPrecedence::Repeat,
+            ExprKind::Paren(..) => ExprPrecedence::Paren,
+            ExprKind::Try(..) => ExprPrecedence::Try,
+            ExprKind::Yield(..) => ExprPrecedence::Yield,
+        }
+    }
 }
 
 impl fmt::Debug for Expr {

src/libsyntax/print/pprust.rs

@@ -1839,7 +1839,7 @@ fn print_call_post(&mut self, args: &[P<ast::Expr>]) -> io::Result<()> {
     }
 
     pub fn print_expr_maybe_paren(&mut self, expr: &ast::Expr, prec: i8) -> io::Result<()> {
-        let needs_par = parser::expr_precedence(expr) < prec;
+        let needs_par = expr.precedence().order() < prec;
         if needs_par {
             self.popen()?;
         }

src/libsyntax/util/parser.rs

@@ -9,7 +9,9 @@
 // except according to those terms.
 use parse::token::{Token, BinOpToken};
 use symbol::keywords;
-use ast::{self, BinOpKind, ExprKind};
+use ast::{self, BinOpKind};
+
+use std::cmp::Ordering;
 
 /// Associative operator with precedence.
 ///
@@ -228,66 +230,130 @@ pub fn to_ast_binop(&self) -> Option<BinOpKind> {
 pub const PREC_PAREN: i8 = 99;
 pub const PREC_FORCE_PAREN: i8 = 100;
 
-pub fn expr_precedence(expr: &ast::Expr) -> i8 {
-    match expr.node {
-        ExprKind::Closure(..) => PREC_CLOSURE,
-
-        ExprKind::Break(..) |
-        ExprKind::Continue(..) |
-        ExprKind::Ret(..) |
-        ExprKind::Yield(..) => PREC_JUMP,
-
-        // `Range` claims to have higher precedence than `Assign`, but `x .. x = x` fails to parse,
-        // instead of parsing as `(x .. x) = x`.  Giving `Range` a lower precedence ensures that
-        // `pprust` will add parentheses in the right places to get the desired parse.
-        ExprKind::Range(..) => PREC_RANGE,
-
-        // Binop-like expr kinds, handled by `AssocOp`.
-        ExprKind::Binary(op, _, _) =>
-            AssocOp::from_ast_binop(op.node).precedence() as i8,
-
-        ExprKind::InPlace(..) => AssocOp::Inplace.precedence() as i8,
-        ExprKind::Cast(..) => AssocOp::As.precedence() as i8,
-        ExprKind::Type(..) => AssocOp::Colon.precedence() as i8,
-
-        ExprKind::Assign(..) |
-        ExprKind::AssignOp(..) => AssocOp::Assign.precedence() as i8,
-
-        // Unary, prefix
-        ExprKind::Box(..) |
-        ExprKind::AddrOf(..) |
-        ExprKind::Unary(..) => PREC_PREFIX,
-
-        // Unary, postfix
-        ExprKind::Call(..) |
-        ExprKind::MethodCall(..) |
-        ExprKind::Field(..) |
-        ExprKind::TupField(..) |
-        ExprKind::Index(..) |
-        ExprKind::Try(..) |
-        ExprKind::InlineAsm(..) |
-        ExprKind::Mac(..) => PREC_POSTFIX,
-
-        // Never need parens
-        ExprKind::Array(..) |
-        ExprKind::Repeat(..) |
-        ExprKind::Tup(..) |
-        ExprKind::Lit(..) |
-        ExprKind::Path(..) |
-        ExprKind::Paren(..) |
-        ExprKind::If(..) |
-        ExprKind::IfLet(..) |
-        ExprKind::While(..) |
-        ExprKind::WhileLet(..) |
-        ExprKind::ForLoop(..) |
-        ExprKind::Loop(..) |
-        ExprKind::Match(..) |
-        ExprKind::Block(..) |
-        ExprKind::Catch(..) |
-        ExprKind::Struct(..) => PREC_PAREN,
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ExprPrecedence {
+    Closure,
+    Break,
+    Continue,
+    Ret,
+    Yield,
+
+    Range,
+
+    Binary(BinOpKind),
+
+    InPlace,
+    Cast,
+    Type,
+
+    Assign,
+    AssignOp,
+
+    Box,
+    AddrOf,
+    Unary,
+
+    Call,
+    MethodCall,
+    Field,
+    TupField,
+    Index,
+    Try,
+    InlineAsm,
+    Mac,
+
+    Array,
+    Repeat,
+    Tup,
+    Lit,
+    Path,
+    Paren,
+    If,
+    IfLet,
+    While,
+    WhileLet,
+    ForLoop,
+    Loop,
+    Match,
+    Block,
+    Catch,
+    Struct,
+}
+
+impl PartialOrd for ExprPrecedence {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.order().cmp(&other.order()))
+    }
+}
+
+impl Ord for ExprPrecedence {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.order().cmp(&other.order())
     }
 }
 
+impl ExprPrecedence {
+    pub fn order(self) -> i8 {
+        match self {
+            ExprPrecedence::Closure => PREC_CLOSURE,
+
+            ExprPrecedence::Break |
+            ExprPrecedence::Continue |
+            ExprPrecedence::Ret |
+            ExprPrecedence::Yield => PREC_JUMP,
+
+            // `Range` claims to have higher precedence than `Assign`, but `x .. x = x` fails to
+            // parse, instead of parsing as `(x .. x) = x`.  Giving `Range` a lower precedence
+            // ensures that `pprust` will add parentheses in the right places to get the desired
+            // parse.
+            ExprPrecedence::Range => PREC_RANGE,
+
+            // Binop-like expr kinds, handled by `AssocOp`.
+            ExprPrecedence::Binary(op) => AssocOp::from_ast_binop(op).precedence() as i8,
+            ExprPrecedence::InPlace => AssocOp::Inplace.precedence() as i8,
+            ExprPrecedence::Cast => AssocOp::As.precedence() as i8,
+            ExprPrecedence::Type => AssocOp::Colon.precedence() as i8,
+
+            ExprPrecedence::Assign |
+            ExprPrecedence::AssignOp => AssocOp::Assign.precedence() as i8,
+
+            // Unary, prefix
+            ExprPrecedence::Box |
+            ExprPrecedence::AddrOf |
+            ExprPrecedence::Unary => PREC_PREFIX,
+
+            // Unary, postfix
+            ExprPrecedence::Call |
+            ExprPrecedence::MethodCall |
+            ExprPrecedence::Field |
+            ExprPrecedence::TupField |
+            ExprPrecedence::Index |
+            ExprPrecedence::Try |
+            ExprPrecedence::InlineAsm |
+            ExprPrecedence::Mac => PREC_POSTFIX,
+
+            // Never need parens
+            ExprPrecedence::Array |
+            ExprPrecedence::Repeat |
+            ExprPrecedence::Tup |
+            ExprPrecedence::Lit |
+            ExprPrecedence::Path |
+            ExprPrecedence::Paren |
+            ExprPrecedence::If |
+            ExprPrecedence::IfLet |
+            ExprPrecedence::While |
+            ExprPrecedence::WhileLet |
+            ExprPrecedence::ForLoop |
+            ExprPrecedence::Loop |
+            ExprPrecedence::Match |
+            ExprPrecedence::Block |
+            ExprPrecedence::Catch |
+            ExprPrecedence::Struct => PREC_PAREN,
+        }
+    }
+}
+
+
 /// Expressions that syntactically contain an "exterior" struct literal i.e. not surrounded by any
 /// parens or other delimiters, e.g. `X { y: 1 }`, `X { y: 1 }.method()`, `foo == X { y: 1 }` and
 /// `X { y: 1 } == foo` all do, but `(X { y: 1 }) == foo` does not.

src/test/ui/suggestions/numeric-cast-2.rs

+// Copyright 2018 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 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn foo() -> i32 {
+    4
+}
+fn main() {
+    let x: u16 = foo();
+    //~^ ERROR mismatched types
+    let y: i64 = x + x;
+    //~^ ERROR mismatched types
+    let z: i32 = x + x;
+    //~^ ERROR mismatched types
+}

src/test/ui/suggestions/numeric-cast-2.stderr

+error[E0308]: mismatched types
+  --> $DIR/numeric-cast-2.rs:15:18
+   |
+15 |     let x: u16 = foo();
+   |                  ^^^^^ expected u16, found i32
+
+error[E0308]: mismatched types
+  --> $DIR/numeric-cast-2.rs:17:18
+   |
+17 |     let y: i64 = x + x;
+   |                  ^^^^^ expected i64, found u16
+
+error[E0308]: mismatched types
+  --> $DIR/numeric-cast-2.rs:19:18
+   |
+19 |     let z: i32 = x + x;
+   |                  ^^^^^ expected i32, found u16
+
+error: aborting due to 3 previous errors
+

src/test/ui/suggestions/numeric-cast.rs

+// Copyright 2018 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 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+fn foo<N>(_x: N) {}
+
+fn main() {
+    let x_usize: usize = 1;
+    let x_u64: u64 = 2;
+    let x_u32: u32 = 3;
+    let x_u16: u16 = 4;
+    let x_u8: u8 = 5;
+    let x_isize: isize = 6;
+    let x_i64: i64 = 7;
+    let x_i32: i32 = 8;
+    let x_i16: i16 = 9;
+    let x_i8: i8 = 10;
+    let x_f64: f64 = 11.0;
+    let x_f32: f32 = 12.0;
+
+    foo::<usize>(x_usize);
+    foo::<usize>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<usize>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<isize>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_isize);
+    foo::<isize>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<isize>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<u64>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_u64);
+    foo::<u64>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<u64>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<i64>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_i64);
+    foo::<i64>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<i64>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<u32>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_u32);
+    foo::<u32>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<u32>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<i32>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_i32);
+    foo::<i32>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<i32>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<u16>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_u16);
+    foo::<u16>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<u16>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<i16>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_i16);
+    foo::<i16>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<i16>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<u8>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_u8);
+    foo::<u8>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<u8>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<i8>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_i8);
+    foo::<i8>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<i8>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<f64>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<f64>(x_f64);
+    foo::<f64>(x_f32);
+    //~^ ERROR mismatched types
+
+    foo::<f32>(x_usize);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_u64);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_u32);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_u16);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_u8);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_isize);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_i64);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_i32);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_i16);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_i8);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_f64);
+    //~^ ERROR mismatched types
+    foo::<f32>(x_f32);
+}