Use token::Lit in ast::ExprKind::Lit.

Instead of `ast::Lit`.

Literal lowering now happens at two different times. Expression literals
are lowered when HIR is crated. Attribute literals are lowered during
parsing.

This commit changes the language very slightly. Some programs that used
to not compile now will compile. This is because some invalid literals
that are removed by `cfg` or attribute macros will no longer trigger
errors. See this comment for more details:
rust-lang#102944 (comment)

Author: nnethercote

src/attr.rs

@@ -260,7 +260,9 @@ impl Rewrite for ast::NestedMetaItem {
     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
         match self {
             ast::NestedMetaItem::MetaItem(ref meta_item) => meta_item.rewrite(context, shape),
-            ast::NestedMetaItem::Literal(ref l) => rewrite_literal(context, l, shape),
+            ast::NestedMetaItem::Literal(ref l) => {
+                rewrite_literal(context, l.token_lit, l.span, shape)
+            }
         }
     }
 }
@@ -318,7 +320,7 @@ impl Rewrite for ast::MetaItem {
                 // we might be better off ignoring the fact that the attribute
                 // is longer than the max width and continue on formatting.
                 // See #2479 for example.
-                let value = rewrite_literal(context, literal, lit_shape)
+                let value = rewrite_literal(context, literal.token_lit, literal.span, lit_shape)
                     .unwrap_or_else(|| context.snippet(literal.span).to_owned());
                 format!("{} = {}", path, value)
             }

src/expr.rs

@@ -3,7 +3,7 @@ use std::cmp::min;
 
 use itertools::Itertools;
 use rustc_ast::token::{Delimiter, LitKind};
-use rustc_ast::{ast, ptr};
+use rustc_ast::{ast, ptr, token};
 use rustc_span::{BytePos, Span};
 
 use crate::chains::rewrite_chain;
@@ -75,12 +75,12 @@ pub(crate) fn format_expr(
             choose_separator_tactic(context, expr.span),
             None,
         ),
-        ast::ExprKind::Lit(ref l) => {
-            if let Some(expr_rw) = rewrite_literal(context, l, shape) {
+        ast::ExprKind::Lit(token_lit) => {
+            if let Some(expr_rw) = rewrite_literal(context, token_lit, expr.span, shape) {
                 Some(expr_rw)
             } else {
-                if let LitKind::StrRaw(_) = l.token_lit.kind {
-                    Some(context.snippet(l.span).trim().into())
+                if let LitKind::StrRaw(_) = token_lit.kind {
+                    Some(context.snippet(expr.span).trim().into())
                 } else {
                     None
                 }
@@ -274,9 +274,9 @@ pub(crate) fn format_expr(
 
             fn needs_space_before_range(context: &RewriteContext<'_>, lhs: &ast::Expr) -> bool {
                 match lhs.kind {
-                    ast::ExprKind::Lit(ref lit) => match lit.kind {
-                        ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
-                            context.snippet(lit.span).ends_with('.')
+                    ast::ExprKind::Lit(token_lit) => match token_lit.kind {
+                        token::LitKind::Float if token_lit.suffix.is_none() => {
+                            context.snippet(lhs.span).ends_with('.')
                         }
                         _ => false,
                     },
@@ -1185,14 +1185,15 @@ pub(crate) fn is_unsafe_block(block: &ast::Block) -> bool {
 
 pub(crate) fn rewrite_literal(
     context: &RewriteContext<'_>,
-    l: &ast::Lit,
+    token_lit: token::Lit,
+    span: Span,
     shape: Shape,
 ) -> Option<String> {
-    match l.kind {
-        ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
-        ast::LitKind::Int(..) => rewrite_int_lit(context, l, shape),
+    match token_lit.kind {
+        token::LitKind::Str => rewrite_string_lit(context, span, shape),
+        token::LitKind::Integer => rewrite_int_lit(context, token_lit, span, shape),
         _ => wrap_str(
-            context.snippet(l.span).to_owned(),
+            context.snippet(span).to_owned(),
             context.config.max_width(),
             shape,
         ),
@@ -1225,9 +1226,13 @@ fn rewrite_string_lit(context: &RewriteContext<'_>, span: Span, shape: Shape) ->
     )
 }
 
-fn rewrite_int_lit(context: &RewriteContext<'_>, lit: &ast::Lit, shape: Shape) -> Option<String> {
-    let span = lit.span;
-    let symbol = lit.token_lit.symbol.as_str();
+fn rewrite_int_lit(
+    context: &RewriteContext<'_>,
+    token_lit: token::Lit,
+    span: Span,
+    shape: Shape,
+) -> Option<String> {
+    let symbol = token_lit.symbol.as_str();
 
     if let Some(symbol_stripped) = symbol.strip_prefix("0x") {
         let hex_lit = match context.config.hex_literal_case() {
@@ -1240,9 +1245,7 @@ fn rewrite_int_lit(context: &RewriteContext<'_>, lit: &ast::Lit, shape: Shape) -
                 format!(
                     "0x{}{}",
                     hex_lit,
-                    lit.token_lit
-                        .suffix
-                        .map_or(String::new(), |s| s.to_string())
+                    token_lit.suffix.map_or(String::new(), |s| s.to_string())
                 ),
                 context.config.max_width(),
                 shape,