From 61ece4ca3ca0bc893fccd0cf1d26deb2c5dd8c74 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Thu, 6 Oct 2022 17:36:06 -0700
Subject: [PATCH] Fix left shift after macro metavariable in type position

---
 src/expr.rs | 12 +++++++++---
 src/ty.rs   | 24 ++++++++++++++++++------
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/src/expr.rs b/src/expr.rs
index fbab681474..93a59b0e20 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -1371,7 +1371,9 @@ pub(crate) mod parsing {
                 });
             } else if Precedence::Cast >= base && input.peek(Token![as]) {
                 let as_token: Token![as] = input.parse()?;
-                let ty = input.call(Type::without_plus)?;
+                let allow_plus = false;
+                let allow_group_generic = false;
+                let ty = ty::parsing::ambig_ty(input, allow_plus, allow_group_generic)?;
                 check_cast(input)?;
                 lhs = Expr::Cast(ExprCast {
                     attrs: Vec::new(),
@@ -1381,7 +1383,9 @@ pub(crate) mod parsing {
                 });
             } else if Precedence::Cast >= base && input.peek(Token![:]) && !input.peek(Token![::]) {
                 let colon_token: Token![:] = input.parse()?;
-                let ty = input.call(Type::without_plus)?;
+                let allow_plus = false;
+                let allow_group_generic = false;
+                let ty = ty::parsing::ambig_ty(input, allow_plus, allow_group_generic)?;
                 check_cast(input)?;
                 lhs = Expr::Type(ExprType {
                     attrs: Vec::new(),
@@ -1429,7 +1433,9 @@ pub(crate) mod parsing {
                 });
             } else if Precedence::Cast >= base && input.peek(Token![as]) {
                 let as_token: Token![as] = input.parse()?;
-                let ty = input.call(Type::without_plus)?;
+                let allow_plus = false;
+                let allow_group_generic = false;
+                let ty = ty::parsing::ambig_ty(input, allow_plus, allow_group_generic)?;
                 check_cast(input)?;
                 lhs = Expr::Cast(ExprCast {
                     attrs: Vec::new(),
diff --git a/src/ty.rs b/src/ty.rs
index 3322709294..4068be3c75 100644
--- a/src/ty.rs
+++ b/src/ty.rs
@@ -343,7 +343,8 @@ pub mod parsing {
     impl Parse for Type {
         fn parse(input: ParseStream) -> Result<Self> {
             let allow_plus = true;
-            ambig_ty(input, allow_plus)
+            let allow_group_generic = true;
+            ambig_ty(input, allow_plus, allow_group_generic)
         }
     }
 
@@ -356,11 +357,16 @@ pub mod parsing {
         #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
         pub fn without_plus(input: ParseStream) -> Result<Self> {
             let allow_plus = false;
-            ambig_ty(input, allow_plus)
+            let allow_group_generic = true;
+            ambig_ty(input, allow_plus, allow_group_generic)
         }
     }
 
-    fn ambig_ty(input: ParseStream, allow_plus: bool) -> Result<Type> {
+    pub(crate) fn ambig_ty(
+        input: ParseStream,
+        allow_plus: bool,
+        allow_group_generic: bool,
+    ) -> Result<Type> {
         let begin = input.fork();
 
         if input.peek(token::Group) {
@@ -381,7 +387,9 @@ pub mod parsing {
                         path: Path::parse_helper(input, false)?,
                     }));
                 }
-            } else if input.peek(Token![<]) || input.peek(Token![::]) && input.peek3(Token![<]) {
+            } else if input.peek(Token![<]) && allow_group_generic
+                || input.peek(Token![::]) && input.peek3(Token![<])
+            {
                 if let Type::Path(mut ty) = *group.elem {
                     let arguments = &mut ty.path.segments.last_mut().unwrap().arguments;
                     if let PathArguments::None = arguments {
@@ -863,7 +871,8 @@ pub mod parsing {
         pub(crate) fn parse(input: ParseStream, allow_plus: bool) -> Result<Self> {
             if input.peek(Token![->]) {
                 let arrow = input.parse()?;
-                let ty = ambig_ty(input, allow_plus)?;
+                let allow_group_generic = true;
+                let ty = ambig_ty(input, allow_plus, allow_group_generic)?;
                 Ok(ReturnType::Type(arrow, Box::new(ty)))
             } else {
                 Ok(ReturnType::Default)
@@ -986,7 +995,10 @@ pub mod parsing {
             let content;
             Ok(TypeParen {
                 paren_token: parenthesized!(content in input),
-                elem: Box::new(ambig_ty(&content, allow_plus)?),
+                elem: Box::new({
+                    let allow_group_generic = true;
+                    ambig_ty(&content, allow_plus, allow_group_generic)?
+                }),
             })
         }
     }