Stop using `String` for error codes.

Error codes are integers, but `String` is used everywhere to represent
them. Gross!

This commit introduces `ErrCode`, an integral newtype for error codes,
replacing `String`. It also introduces a constant for every error code,
e.g. `E0123`, and removes the `error_code!` macro. The constants are
imported wherever used with `use rustc_errors::codes::*`.

With the old code, we have three different ways to specify an error code
at a use point:
```
error_code!(E0123)  // macro call

struct_span_code_err!(dcx, span, E0123, "msg");  // bare ident arg to macro call

\#[diag(name, code = "E0123")]  // string
struct Diag;
```

With the new code, they all use the `E0123` constant.
```
E0123  // constant

struct_span_code_err!(dcx, span, E0123, "msg");  // constant

\#[diag(name, code = E0123)]  // constant
struct Diag;
```

The commit also changes the structure of the error code definitions:
- `rustc_error_codes` now just defines a higher-order macro listing the
  used error codes and nothing else.
- Because that's now the only thing in the `rustc_error_codes` crate, I
  moved it into the `lib.rs` file and removed the `error_codes.rs` file.
- `rustc_errors` uses that macro to define everything, e.g. the error
  code constants and the `DIAGNOSTIC_TABLES`. This is in its new
  `codes.rs` file.

1 files changed, 7 insertions, 7 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
index 39bc2b960e9..fb705d91977 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
@@ -2,7 +2,7 @@
 
 use hir::def_id::LocalDefId;
 use hir::{ConstContext, LangItem};
-use rustc_errors::{error_code, DiagnosticBuilder};
+use rustc_errors::{codes::*, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
@@ -372,7 +372,7 @@ impl<'tcx> NonConstOp<'tcx> for HeapAllocation {
         ccx.dcx().create_err(errors::UnallowedHeapAllocations {
             span,
             kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(&error_code!(E0010)).then_some(()),
+            teach: ccx.tcx.sess.teach(E0010).then_some(()),
         })
     }
 }
@@ -434,14 +434,14 @@ impl<'tcx> NonConstOp<'tcx> for CellBorrow {
                 span,
                 opt_help: Some(()),
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0492)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0492).then_some(()),
             })
         } else {
             ccx.dcx().create_err(errors::InteriorMutableDataRefer {
                 span,
                 opt_help: None,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0492)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0492).then_some(()),
             })
         }
     }
@@ -469,12 +469,12 @@ impl<'tcx> NonConstOp<'tcx> for MutBorrow {
             hir::BorrowKind::Raw => ccx.tcx.dcx().create_err(errors::UnallowedMutableRaw {
                 span,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0764)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0764).then_some(()),
             }),
             hir::BorrowKind::Ref => ccx.dcx().create_err(errors::UnallowedMutableRefs {
                 span,
                 kind: ccx.const_kind(),
-                teach: ccx.tcx.sess.teach(&error_code!(E0764)).then_some(()),
+                teach: ccx.tcx.sess.teach(E0764).then_some(()),
             }),
         }
     }
@@ -588,7 +588,7 @@ impl<'tcx> NonConstOp<'tcx> for StaticAccess {
         ccx.dcx().create_err(errors::StaticAccessErr {
             span,
             kind: ccx.const_kind(),
-            teach: ccx.tcx.sess.teach(&error_code!(E0013)).then_some(()),
+            teach: ccx.tcx.sess.teach(E0013).then_some(()),
         })
     }
 }