Restrict value in key-value attributes to literals

src/libsyntax/parse/attr.rs

@@ -158,11 +158,21 @@ impl<'a> Parser<'a> {
                    self.parse_token_tree().into()
             } else if self.eat(&token::Eq) {
                 let eq = TokenTree::Token(self.prev_span, token::Eq);
-                let tree = match self.token {
-                    token::CloseDelim(_) | token::Eof => self.unexpected()?,
-                    _ => self.parse_token_tree(),
+                let mut is_interpolated_expr = false;
+                if let token::Interpolated(nt) = &self.token {
+                    if let token::NtExpr(..) = **nt {
+                        is_interpolated_expr = true;
+                    }
+                }
+                let tokens = if is_interpolated_expr {
+                    // We need to accept arbitrary interpolated expressions to continue
+                    // supporting things like `doc = $expr` that work on stable.
+                    // Non-literal interpolated expressions are rejected after expansion.
+                    self.parse_token_tree().into()
+                } else {
+                    self.parse_unsuffixed_lit()?.tokens()
                 };
-                TokenStream::new(vec![eq.into(), tree.into()])
+                TokenStream::from_streams(vec![eq.into(), tokens])
             } else {
                 TokenStream::empty()
             };

src/libsyntax/tokenstream.rs

@@ -254,7 +254,7 @@ impl TokenStream {
         }
     }
 
-    fn from_streams(mut streams: Vec<TokenStream>) -> TokenStream {
+    pub(crate) fn from_streams(mut streams: Vec<TokenStream>) -> TokenStream {
         match streams.len() {
             0 => TokenStream::empty(),
             1 => streams.pop().unwrap(),

src/test/ui/attr-eq-token-tree.rs

@@ -1,6 +1,4 @@
-// compile-pass
-
 #![feature(custom_attribute, unrestricted_attribute_tokens)]
 
-#[my_attr = !] // OK under feature gate
+#[my_attr = !] //~ ERROR unexpected token: `!`
 fn main() {}

src/test/ui/attr-eq-token-tree.stderr

@@ -0,0 +1,8 @@
+error: unexpected token: `!`
+  --> $DIR/attr-eq-token-tree.rs:3:11
+   |
+LL | #[my_attr = !] //~ ERROR unexpected token: `!`
+   |           ^
+
+error: aborting due to previous error
+

src/test/ui/macros/macro-attribute.rs

@@ -1,4 +1,4 @@
 #![feature(unrestricted_attribute_tokens)]
 
-#[doc = $not_there] //~ ERROR expected `]`, found `not_there`
+#[doc = $not_there] //~ ERROR unexpected token: `$`
 fn main() { }

src/test/ui/macros/macro-attribute.stderr

@@ -1,8 +1,8 @@
-error: expected `]`, found `not_there`
-  --> $DIR/macro-attribute.rs:3:10
+error: unexpected token: `$`
+  --> $DIR/macro-attribute.rs:3:7
    |
-LL | #[doc = $not_there] //~ ERROR expected `]`, found `not_there`
-   |          ^^^^^^^^^ expected `]`
+LL | #[doc = $not_there] //~ ERROR unexpected token: `$`
+   |       ^
 
 error: aborting due to previous error
 

src/test/ui/malformed/malformed-interpolated.rs

@@ -0,0 +1,18 @@
+#![feature(custom_attribute)]
+
+macro_rules! check {
+    ($expr: expr) => (
+        #[my_attr = $expr] //~ ERROR suffixed literals are not allowed in attributes
+                           //~| ERROR unexpected token: `-0`
+                           //~| ERROR unexpected token: `0 + 0`
+        use main as _;
+    );
+}
+
+check!("0"); // OK
+check!(0); // OK
+check!(0u8); // ERROR, see above
+check!(-0); // ERROR, see above
+check!(0 + 0); // ERROR, see above
+
+fn main() {}

src/test/ui/malformed/malformed-interpolated.stderr

@@ -0,0 +1,35 @@
+error: suffixed literals are not allowed in attributes
+  --> $DIR/malformed-interpolated.rs:5:21
+   |
+LL |         #[my_attr = $expr] //~ ERROR suffixed literals are not allowed in attributes
+   |                     ^^^^^
+...
+LL | check!(0u8); // ERROR, see above
+   | ------------ in this macro invocation
+   |
+   = help: instead of using a suffixed literal (1u8, 1.0f32, etc.), use an unsuffixed version (1, 1.0, etc.).
+
+error: unexpected token: `-0`
+  --> $DIR/malformed-interpolated.rs:5:19
+   |
+LL |         #[my_attr = $expr] //~ ERROR suffixed literals are not allowed in attributes
+   |                   ^
+...
+LL | check!(-0); // ERROR, see above
+   | ----------- in this macro invocation
+   |
+   = help: try enabling `#![feature(unrestricted_attribute_tokens)]`
+
+error: unexpected token: `0 + 0`
+  --> $DIR/malformed-interpolated.rs:5:19
+   |
+LL |         #[my_attr = $expr] //~ ERROR suffixed literals are not allowed in attributes
+   |                   ^
+...
+LL | check!(0 + 0); // ERROR, see above
+   | -------------- in this macro invocation
+   |
+   = help: try enabling `#![feature(unrestricted_attribute_tokens)]`
+
+error: aborting due to 3 previous errors
+

src/test/ui/parser/attr-bad-meta-2.stderr

@@ -1,8 +1,8 @@
 error: unexpected token: `]`
-  --> $DIR/attr-bad-meta-2.rs:1:9
+  --> $DIR/attr-bad-meta-2.rs:1:8
    |
 LL | #[path =] //~ ERROR unexpected token: `]`
-   |         ^ unexpected token after this
+   |        ^
 
 error: aborting due to previous error
 

src/test/ui/proc-macro/proc-macro-gates.rs

@@ -19,7 +19,7 @@ mod _test2_inner {
           //~| ERROR: non-builtin inner attributes are unstable
 }
 
-#[a = y] //~ ERROR: must only be followed by a delimiter token
+#[a = "y"] //~ ERROR: must only be followed by a delimiter token
 fn _test3() {}
 
 fn attrs() {

src/test/ui/proc-macro/proc-macro-gates.stderr

@@ -33,8 +33,8 @@ LL |     #![a] //~ ERROR: custom attributes cannot be applied to modules
 error: custom attribute invocations must be of the form #[foo] or #[foo(..)], the macro name must only be followed by a delimiter token
   --> $DIR/proc-macro-gates.rs:22:1
    |
-LL | #[a = y] //~ ERROR: must only be followed by a delimiter token
-   | ^^^^^^^^
+LL | #[a = "y"] //~ ERROR: must only be followed by a delimiter token
+   | ^^^^^^^^^^
 
 error[E0658]: custom attributes cannot be applied to statements (see issue #54727)
   --> $DIR/proc-macro-gates.rs:31:5