Parse field default values

src/data.rs

@@ -200,6 +200,8 @@ ast_struct! {
         pub colon_token: Option<Token![:]>,
 
         pub ty: Type,
+
+        pub default: Option<(Token![=], Expr)>,
     }
 }
 
@@ -380,26 +382,52 @@ pub(crate) mod parsing {
                 input.parse()?
             };
 
+            let default = if input.peek(Token![=]) {
+                let eq_token: Token![=] = input.parse()?;
+                let expr: Expr = input.parse()?;
+                Some((eq_token, expr))
+            } else {
+                None
+            };
+
             Ok(Field {
                 attrs,
                 vis,
                 modifiers: FieldModifiers {},
                 ident: Some(ident),
                 colon_token: Some(colon_token),
                 ty,
+                default,
             })
         }
 
         /// Parses an unnamed (tuple struct) field.
         #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
         pub fn parse_unnamed(input: ParseStream) -> Result<Self> {
+            let attrs = input.call(Attribute::parse_outer)?;
+            let vis: Visibility = input.parse()?;
+            let ty: Type = input.parse()?;
+
+            if input.peek(Token![=]) {
+                input.parse::<Token![=]>()?;
+                let start_span = input.span();
+                input.parse::<Expr>()?;
+                let end_span = input.cursor().prev_span();
+                return Err(crate::error::new2(
+                    start_span,
+                    end_span,
+                    "field default value is only supported in structs with named fields",
+                ));
+            }
+
             Ok(Field {
-                attrs: input.call(Attribute::parse_outer)?,
-                vis: input.parse()?,
+                attrs,
+                vis,
                 modifiers: FieldModifiers {},
                 ident: None,
                 colon_token: None,
-                ty: input.parse()?,
+                ty,
+                default: None,
             })
         }
     }
@@ -453,6 +481,10 @@ mod printing {
                 TokensOrDefault(&self.colon_token).to_tokens(tokens);
             }
             self.ty.to_tokens(tokens);
+            if let Some((eq_token, default)) = &self.default {
+                eq_token.to_tokens(tokens);
+                default.to_tokens(tokens);
+            }
         }
     }
 }

src/parse_quote.rs

@@ -154,7 +154,7 @@ impl<T: Parse> ParseQuote for T {
 
 use crate::punctuated::Punctuated;
 #[cfg(any(feature = "full", feature = "derive"))]
-use crate::{attr, Attribute, Field, FieldModifiers, Ident, Type, Visibility};
+use crate::{attr, Attribute, Expr, Field, FieldModifiers, Ident, Type, Visibility};
 #[cfg(feature = "full")]
 use crate::{Arm, Block, Pat, Safety, Stmt};
 
@@ -199,13 +199,22 @@ impl ParseQuote for Field {
 
         let ty: Type = input.parse()?;
 
+        let default = if is_named && input.peek(Token![=]) {
+            let eq_token: Token![=] = input.parse()?;
+            let expr: Expr = input.parse()?;
+            Some((eq_token, expr))
+        } else {
+            None
+        };
+
         Ok(Field {
             attrs,
             vis,
             modifiers: FieldModifiers {},
             ident,
             colon_token,
             ty,
+            default,
         })
     }
 }

tests/repo/mod.rs

@@ -64,6 +64,7 @@ static EXCLUDE_FILES: &[&str] = &[
     "tests/ui/consts/trait_alias_method_call.rs",
     "tests/ui/generic-const-items/const-trait-impl.rs",
     "tests/ui/parser/impls-nested-within-fns-semantic-1.rs",
+    "tests/ui/structs/default-field-values/support.rs",
     "tests/ui/traits/const-traits/assoc-type-const-bound-usage-0.rs",
     "tests/ui/traits/const-traits/assoc-type-const-bound-usage-1.rs",
     "tests/ui/traits/const-traits/auxiliary/associated-const-stability.rs",
@@ -232,32 +233,6 @@ static EXCLUDE_FILES: &[&str] = &[
     "tests/ui/pattern/rfc-3637-guard-patterns/only-gather-locals-once.rs",
     "tests/ui/reachable/guard_read_for_never.rs",
 
-    // TODO: struct field default: `struct S { field: i32 = 1 }`
-    // https://github.com/dtolnay/syn/issues/1774
-    "compiler/rustc_ast_lowering/src/delegation/generics.rs",
-    "compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs",
-    "compiler/rustc_errors/src/markdown/parse.rs",
-    "compiler/rustc_hir/src/attrs/diagnostic.rs",
-    "compiler/rustc_hir_analysis/src/hir_wf_check.rs",
-    "compiler/rustc_middle/src/hir/map.rs",
-    "compiler/rustc_middle/src/ty/mod.rs",
-    "compiler/rustc_parse/src/parser/mod.rs",
-    "compiler/rustc_parse/src/parser/stmt.rs",
-    "compiler/rustc_privacy/src/lib.rs",
-    "compiler/rustc_resolve/src/imports.rs",
-    "compiler/rustc_resolve/src/lib.rs",
-    "compiler/rustc_session/src/config.rs",
-    "compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs",
-    "src/tools/clippy/tests/ui/exhaustive_items.rs",
-    "src/tools/rust-analyzer/crates/parser/test_data/parser/inline/ok/record_field_default_values.rs",
-    "src/tools/rustfmt/tests/source/default-field-values.rs",
-    "src/tools/rustfmt/tests/target/default-field-values.rs",
-    "tests/ui/structs/default-field-values/auxiliary/struct_field_default.rs",
-    "tests/ui/structs/default-field-values/const-trait-default-field-value.rs",
-    "tests/ui/structs/default-field-values/field-references-param.rs",
-    "tests/ui/structs/default-field-values/support.rs",
-    "tests/ui/structs/default-field-values/use-normalized-ty-for-default-struct-value.rs",
-
     // TODO: final associated functions: `final fn`
     // https://github.com/dtolnay/syn/issues/1981
     "library/core/src/io/size_hint.rs",