lit_to_const: gracefully bubble up type errors.

Author: Centril

src/librustc/mir/interpret/mod.rs

@@ -162,6 +162,10 @@ pub struct LitToConstInput<'tcx> {
 /// Error type for `tcx.lit_to_const`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable)]
 pub enum LitToConstError {
+    /// The literal's inferred type did not match the expected `ty` in the input.
+    /// This is used for graceful error handling (`delay_span_bug`) in
+    /// type checking (`AstConv::ast_const_to_const`).
+    TypeError,
     UnparseableFloat,
     Reported,
 }

src/librustc_mir_build/hair/constant.rs

@@ -1,7 +1,7 @@
 use rustc::mir::interpret::{
     truncate, Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
 };
-use rustc::ty::{self, layout::Size, ParamEnv, TyCtxt};
+use rustc::ty::{self, layout::Size, ParamEnv, TyCtxt, TyS};
 use rustc_span::symbol::Symbol;
 use syntax::ast;
 
@@ -20,50 +20,35 @@ crate fn lit_to_const<'tcx>(
         Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
     };
 
-    let lit = match *lit {
-        ast::LitKind::Str(ref s, _) => {
+    let lit = match (lit, &ty.kind) {
+        (ast::LitKind::Str(s, _), ty::Ref(_, TyS { kind: ty::Str, .. }, _)) => {
             let s = s.as_str();
             let allocation = Allocation::from_byte_aligned_bytes(s.as_bytes());
             let allocation = tcx.intern_const_alloc(allocation);
             ConstValue::Slice { data: allocation, start: 0, end: s.len() }
         }
-        ast::LitKind::ByteStr(ref data) => {
-            if let ty::Ref(_, ref_ty, _) = ty.kind {
-                match ref_ty.kind {
-                    ty::Slice(_) => {
-                        let allocation = Allocation::from_byte_aligned_bytes(data as &Vec<u8>);
-                        let allocation = tcx.intern_const_alloc(allocation);
-                        ConstValue::Slice { data: allocation, start: 0, end: data.len() }
-                    }
-                    ty::Array(_, _) => {
-                        let id = tcx.allocate_bytes(data);
-                        ConstValue::Scalar(Scalar::Ptr(id.into()))
-                    }
-                    _ => {
-                        bug!("bytestring should have type of either &[u8] or &[u8; _], not {}", ty)
-                    }
-                }
-            } else {
-                bug!("bytestring should have type of either &[u8] or &[u8; _], not {}", ty)
-            }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, TyS { kind: ty::Slice(_), .. }, _)) => {
+            let allocation = Allocation::from_byte_aligned_bytes(data as &Vec<u8>);
+            let allocation = tcx.intern_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: data.len() }
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, TyS { kind: ty::Array(_, _), .. }, _)) => {
+            let id = tcx.allocate_bytes(data);
+            ConstValue::Scalar(Scalar::Ptr(id.into()))
+        }
+        (ast::LitKind::Byte(n), ty::Uint(ast::UintTy::U8)) => {
+            ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
         }
-        ast::LitKind::Byte(n) => ConstValue::Scalar(Scalar::from_uint(n, Size::from_bytes(1))),
-        ast::LitKind::Int(n, _) if neg => {
-            let n = n as i128;
-            let n = n.overflowing_neg().0;
-            trunc(n as u128)?
+        (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
+            trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
         }
-        ast::LitKind::Int(n, _) => trunc(n)?,
-        ast::LitKind::Float(n, _) => {
-            let fty = match ty.kind {
-                ty::Float(fty) => fty,
-                _ => bug!(),
-            };
-            parse_float(n, fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
+        (ast::LitKind::Float(n, _), ty::Float(fty)) => {
+            parse_float(*n, *fty, neg).map_err(|_| LitToConstError::UnparseableFloat)?
         }
-        ast::LitKind::Bool(b) => ConstValue::Scalar(Scalar::from_bool(b)),
-        ast::LitKind::Char(c) => ConstValue::Scalar(Scalar::from_char(c)),
-        ast::LitKind::Err(_) => return Err(LitToConstError::Reported),
+        (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
+        (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
+        (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
+        _ => return Err(LitToConstError::TypeError),
     };
     Ok(tcx.mk_const(ty::Const { val: ty::ConstKind::Value(lit), ty }))
 }

src/librustc_mir_build/hair/cx/mod.rs

@@ -148,6 +148,7 @@ impl<'a, 'tcx> Cx<'a, 'tcx> {
                 // create a dummy value and continue compiling
                 Const::from_bits(self.tcx, 0, self.param_env.and(ty))
             }
+            Err(LitToConstError::TypeError) => bug!("const_eval_literal: had type error"),
         }
     }
 

src/librustc_mir_build/hair/pattern/mod.rs

@@ -843,6 +843,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     PatKind::Wild
                 }
                 Err(LitToConstError::Reported) => PatKind::Wild,
+                Err(LitToConstError::TypeError) => bug!("lower_lit: had type error"),
             }
         }
     }

src/librustc_typeck/astconv.rs

@@ -2738,6 +2738,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // mir.
             if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
                 return c;
+            } else {
+                tcx.sess.delay_span_bug(expr.span, "ast_const_to_const: couldn't lit_to_const");
             }
         }
 

src/test/ui/consts/issue-69310-array-size-lit-wrong-ty.rs

@@ -0,0 +1,11 @@
+// This is a regression test for #69310, which was injected by #68118.
+// The issue here was that as a performance optimization,
+// we call the query `lit_to_const(input);`.
+// However, the literal `input.lit` would not be of the type expected by `input.ty`.
+// As a result, we immediately called `bug!(...)` instead of bubbling up the problem
+// so that it could be handled by the caller of `lit_to_const` (`ast_const_to_const`).
+
+fn main() {}
+
+const A: [(); 0.1] = [()]; //~ ERROR mismatched types
+const B: [(); b"a"] = [()]; //~ ERROR mismatched types

src/test/ui/consts/issue-69310-array-size-lit-wrong-ty.stderr

@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-69310-array-size-lit-wrong-ty.rs:10:15
+   |
+LL | const A: [(); 0.1] = [()];
+   |               ^^^ expected `usize`, found floating-point number
+
+error[E0308]: mismatched types
+  --> $DIR/issue-69310-array-size-lit-wrong-ty.rs:11:15
+   |
+LL | const B: [(); b"a"] = [()];
+   |               ^^^^ expected `usize`, found `&[u8; 1]`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.