From f1ca210cc4772f198af91886e3849dac68114f97 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 11 Jul 2024 16:07:12 -0700
Subject: [PATCH 1/2] Add regression test for issue 309

---
 tests/test_display.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/test_display.rs b/tests/test_display.rs
index c05d157..7a9057c 100644
--- a/tests/test_display.rs
+++ b/tests/test_display.rs
@@ -234,6 +234,18 @@ fn test_field() {
     assert("0", Error(Inner { data: 0 }));
 }
 
+#[test]
+fn test_nested_tuple_field() {
+    #[derive(Debug)]
+    struct Inner(usize);
+
+    #[derive(Error, Debug)]
+    #[error("{}", .0.0)]
+    struct Error(Inner);
+
+    assert("0", Error(Inner(0)));
+}
+
 #[test]
 fn test_macro_rules() {
     // Regression test for https://github.com/dtolnay/thiserror/issues/86

From 40a7779b1793f2dce5f85abe8c03486cdb5eb640 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 11 Jul 2024 16:09:19 -0700
Subject: [PATCH 2/2] Support .0.0 nested tuple index

---
 impl/src/attr.rs | 42 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/impl/src/attr.rs b/impl/src/attr.rs
index 395edb1..e0ac02b 100644
--- a/impl/src/attr.rs
+++ b/impl/src/attr.rs
@@ -1,11 +1,11 @@
-use proc_macro2::{Delimiter, Group, Span, TokenStream, TokenTree};
+use proc_macro2::{Delimiter, Group, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
 use quote::{format_ident, quote, ToTokens};
 use std::collections::BTreeSet as Set;
 use syn::parse::discouraged::Speculative;
 use syn::parse::ParseStream;
 use syn::{
-    braced, bracketed, parenthesized, token, Attribute, Error, Ident, Index, LitInt, LitStr, Meta,
-    Result, Token,
+    braced, bracketed, parenthesized, token, Attribute, Error, Ident, Index, LitFloat, LitInt,
+    LitStr, Meta, Result, Token,
 };
 
 pub struct Attrs<'a> {
@@ -145,14 +145,42 @@ fn parse_token_expr(input: ParseStream, mut begin_expr: bool) -> Result<TokenStr
                 input.parse::<Token![.]>()?;
                 begin_expr = false;
                 continue;
-            }
-            if input.peek2(LitInt) {
+            } else if input.peek2(LitInt) {
                 input.parse::<Token![.]>()?;
                 let int: Index = input.parse()?;
-                let ident = format_ident!("_{}", int.index, span = int.span);
-                tokens.push(TokenTree::Ident(ident));
+                tokens.push({
+                    let ident = format_ident!("_{}", int.index, span = int.span);
+                    TokenTree::Ident(ident)
+                });
                 begin_expr = false;
                 continue;
+            } else if input.peek2(LitFloat) {
+                let ahead = input.fork();
+                ahead.parse::<Token![.]>()?;
+                let float: LitFloat = ahead.parse()?;
+                let repr = float.to_string();
+                let mut indices = repr.split('.').map(syn::parse_str::<Index>);
+                if let (Some(Ok(first)), Some(Ok(second)), None) =
+                    (indices.next(), indices.next(), indices.next())
+                {
+                    input.advance_to(&ahead);
+                    tokens.push({
+                        let ident = format_ident!("_{}", first, span = float.span());
+                        TokenTree::Ident(ident)
+                    });
+                    tokens.push({
+                        let mut punct = Punct::new('.', Spacing::Alone);
+                        punct.set_span(float.span());
+                        TokenTree::Punct(punct)
+                    });
+                    tokens.push({
+                        let mut literal = Literal::u32_unsuffixed(second.index);
+                        literal.set_span(float.span());
+                        TokenTree::Literal(literal)
+                    });
+                    begin_expr = false;
+                    continue;
+                }
             }
         }