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.

4 files changed, 20 insertions, 20 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 40852048293..053a9c03d74 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -3,7 +3,7 @@ use std::borrow::Cow;
 use rustc_ast::token::Token;
 use rustc_ast::{Path, Visibility};
 use rustc_errors::{
-    AddToDiagnostic, Applicability, DiagCtxt, DiagnosticBuilder, IntoDiagnostic, Level,
+    codes::*, AddToDiagnostic, Applicability, DiagCtxt, DiagnosticBuilder, IntoDiagnostic, Level,
     SubdiagnosticMessage,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
@@ -25,7 +25,7 @@ pub(crate) struct AmbiguousPlus {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_maybe_recover_from_bad_type_plus, code = "E0178")]
+#[diag(parse_maybe_recover_from_bad_type_plus, code = E0178)]
 pub(crate) struct BadTypePlus {
     pub ty: String,
     #[primary_span]
@@ -807,7 +807,7 @@ pub(crate) struct InclusiveRangeMatchArrow {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_inclusive_range_no_end, code = "E0586")]
+#[diag(parse_inclusive_range_no_end, code = E0586)]
 #[note]
 pub(crate) struct InclusiveRangeNoEnd {
     #[primary_span]
@@ -901,7 +901,7 @@ pub(crate) struct MismatchedClosingDelimiter {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_incorrect_visibility_restriction, code = "E0704")]
+#[diag(parse_incorrect_visibility_restriction, code = E0704)]
 #[help]
 pub(crate) struct IncorrectVisibilityRestriction {
     #[primary_span]
@@ -925,7 +925,7 @@ pub(crate) struct ExpectedStatementAfterOuterAttr {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_doc_comment_does_not_document_anything, code = "E0585")]
+#[diag(parse_doc_comment_does_not_document_anything, code = E0585)]
 #[help]
 pub(crate) struct DocCommentDoesNotDocumentAnything {
     #[primary_span]
@@ -1357,7 +1357,7 @@ pub(crate) struct AttributeOnParamType {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_pattern_method_param_without_body, code = "E0642")]
+#[diag(parse_pattern_method_param_without_body, code = E0642)]
 pub(crate) struct PatternMethodParamWithoutBody {
     #[primary_span]
     #[suggestion(code = "_", applicability = "machine-applicable")]
@@ -1565,7 +1565,7 @@ pub(crate) struct WhereClauseBeforeTupleStructBodySugg {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_async_fn_in_2015, code = "E0670")]
+#[diag(parse_async_fn_in_2015, code = E0670)]
 pub(crate) struct AsyncFnIn2015 {
     #[primary_span]
     #[label]
@@ -1929,7 +1929,7 @@ pub struct CrDocComment {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_no_digits_literal, code = "E0768")]
+#[diag(parse_no_digits_literal, code = E0768)]
 pub struct NoDigitsLiteral {
     #[primary_span]
     pub span: Span,
@@ -2499,7 +2499,7 @@ pub(crate) struct FnPointerCannotBeAsync {
 }
 
 #[derive(Diagnostic)]
-#[diag(parse_nested_c_variadic_type, code = "E0743")]
+#[diag(parse_nested_c_variadic_type, code = E0743)]
 pub(crate) struct NestedCVariadicType {
     #[primary_span]
     pub span: Span,
diff --git a/compiler/rustc_parse/src/lexer/mod.rs b/compiler/rustc_parse/src/lexer/mod.rs
index 20ec4a300c1..31552452676 100644
--- a/compiler/rustc_parse/src/lexer/mod.rs
+++ b/compiler/rustc_parse/src/lexer/mod.rs
@@ -7,7 +7,7 @@ use rustc_ast::ast::{self, AttrStyle};
 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
-use rustc_errors::{error_code, Applicability, DiagCtxt, DiagnosticBuilder, StashKey};
+use rustc_errors::{codes::*, Applicability, DiagCtxt, DiagnosticBuilder, StashKey};
 use rustc_lexer::unescape::{self, EscapeError, Mode};
 use rustc_lexer::{Base, DocStyle, RawStrError};
 use rustc_lexer::{Cursor, LiteralKind};
@@ -397,7 +397,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
                 if !terminated {
                     self.dcx()
                         .struct_span_fatal(self.mk_sp(start, end), "unterminated character literal")
-                        .with_code(error_code!(E0762))
+                        .with_code(E0762)
                         .emit()
                 }
                 self.cook_unicode(token::Char, Mode::Char, start, end, 1, 1) // ' '
@@ -409,7 +409,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated byte constant",
                         )
-                        .with_code(error_code!(E0763))
+                        .with_code(E0763)
                         .emit()
                 }
                 self.cook_unicode(token::Byte, Mode::Byte, start, end, 2, 1) // b' '
@@ -421,7 +421,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
                             self.mk_sp(start, end),
                             "unterminated double quote string",
                         )
-                        .with_code(error_code!(E0765))
+                        .with_code(E0765)
                         .emit()
                 }
                 self.cook_unicode(token::Str, Mode::Str, start, end, 1, 1) // " "
@@ -433,7 +433,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated double quote byte string",
                         )
-                        .with_code(error_code!(E0766))
+                        .with_code(E0766)
                         .emit()
                 }
                 self.cook_unicode(token::ByteStr, Mode::ByteStr, start, end, 2, 1) // b" "
@@ -445,7 +445,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
                             self.mk_sp(start + BytePos(1), end),
                             "unterminated C string",
                         )
-                        .with_code(error_code!(E0767))
+                        .with_code(E0767)
                         .emit()
                 }
                 self.cook_mixed(token::CStr, Mode::CStr, start, end, 2, 1) // c" "
@@ -582,7 +582,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
     ) -> ! {
         let mut err =
             self.dcx().struct_span_fatal(self.mk_sp(start, start), "unterminated raw string");
-        err.code(error_code!(E0748));
+        err.code(E0748);
         err.span_label(self.mk_sp(start, start), "unterminated raw string");
 
         if n_hashes > 0 {
@@ -614,7 +614,7 @@ impl<'sess, 'src> StringReader<'sess, 'src> {
         };
         let last_bpos = self.pos;
         let mut err = self.dcx().struct_span_fatal(self.mk_sp(start, last_bpos), msg);
-        err.code(error_code!(E0758));
+        err.code(E0758);
         let mut nested_block_comment_open_idxs = vec![];
         let mut last_nested_block_comment_idxs = None;
         let mut content_chars = self.str_from(start).char_indices().peekable();
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index a92609c2c2f..98e062dd784 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -8,7 +8,7 @@ use super::{AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle
 use rustc_ast as ast;
 use rustc_ast::attr;
 use rustc_ast::token::{self, Delimiter, Nonterminal};
-use rustc_errors::{error_code, Diagnostic, PResult};
+use rustc_errors::{codes::*, Diagnostic, PResult};
 use rustc_span::{sym, BytePos, Span};
 use thin_vec::ThinVec;
 use tracing::debug;
@@ -61,7 +61,7 @@ impl<'a> Parser<'a> {
                     let mut err = self
                         .dcx()
                         .struct_span_err(span, fluent::parse_inner_doc_comment_not_permitted);
-                    err.code(error_code!(E0753));
+                    err.code(E0753);
                     if let Some(replacement_span) = self.annotate_following_item_if_applicable(
                         &mut err,
                         span,
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 3bd8ae02586..9a77643f951 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -10,7 +10,7 @@ use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
 use rustc_ast::util::case::Case;
 use rustc_ast::{self as ast};
 use rustc_ast_pretty::pprust;
-use rustc_errors::{struct_span_code_err, Applicability, PResult, StashKey};
+use rustc_errors::{codes::*, struct_span_code_err, Applicability, PResult, StashKey};
 use rustc_span::edit_distance::edit_distance;
 use rustc_span::edition::Edition;
 use rustc_span::source_map;