Fix ICE from cfg_attr_trace

compiler/rustc_hir/src/hir.rs

@@ -1304,6 +1304,15 @@ impl Attribute {
             Attribute::Unparsed(_) => false,
         }
     }
+
+    pub fn is_prefix_attr_for_suggestions(&self) -> bool {
+        match self {
+            Attribute::Unparsed(attr) => attr.span.desugaring_kind().is_none(),
+            // Other parsed attributes that can appear on expressions originate from source and
+            // should make suggestions treat the expression like a prefixed form.
+            Attribute::Parsed(_) => true,
+        }
+    }
 }
 
 impl AttributeExt for Attribute {

compiler/rustc_hir_typeck/src/expr.rs

@@ -57,25 +57,7 @@ use crate::{
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub(crate) fn precedence(&self, expr: &hir::Expr<'_>) -> ExprPrecedence {
         let has_attr = |id: HirId| -> bool {
-            for attr in self.tcx.hir_attrs(id) {
-                // For the purpose of rendering suggestions, disregard attributes
-                // that originate from desugaring of any kind. For example, `x?`
-                // desugars to `#[allow(unreachable_code)] match ...`. Failing to
-                // ignore the prefix attribute in the desugaring would cause this
-                // suggestion:
-                //
-                //     let y: u32 = x?.try_into().unwrap();
-                //                    ++++++++++++++++++++
-                //
-                // to be rendered as:
-                //
-                //     let y: u32 = (x?).try_into().unwrap();
-                //                  +  +++++++++++++++++++++
-                if attr.span().desugaring_kind().is_none() {
-                    return true;
-                }
-            }
-            false
+            self.tcx.hir_attrs(id).iter().any(hir::Attribute::is_prefix_attr_for_suggestions)
         };
 
         // Special case: range expressions are desugared to struct literals in HIR,

compiler/rustc_lint/src/context.rs

@@ -845,12 +845,7 @@ impl<'tcx> LateContext<'tcx> {
     /// be used for pretty-printing HIR by rustc_hir_pretty.
     pub fn precedence(&self, expr: &hir::Expr<'_>) -> ExprPrecedence {
         let has_attr = |id: hir::HirId| -> bool {
-            for attr in self.tcx.hir_attrs(id) {
-                if attr.span().desugaring_kind().is_none() {
-                    return true;
-                }
-            }
-            false
+            self.tcx.hir_attrs(id).iter().any(hir::Attribute::is_prefix_attr_for_suggestions)
         };
         expr.precedence(&has_attr)
     }

tests/ui/conditional-compilation/cfg-attr-parsed-span-issue-154801.rs

@@ -0,0 +1,11 @@
+fn main() {
+    let _x = 30;
+    #[cfg_attr(, (cc))] //~ ERROR expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found `,`
+    _x //~ ERROR mismatched types
+}
+
+fn inline_case() {
+    let _x = 30;
+    #[inline] //~ ERROR `#[inline]` attribute cannot be used on expressions
+    _x //~ ERROR mismatched types
+}

tests/ui/conditional-compilation/cfg-attr-parsed-span-issue-154801.stderr

@@ -0,0 +1,42 @@
+error: expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found `,`
+  --> $DIR/cfg-attr-parsed-span-issue-154801.rs:3:16
+   |
+LL |     #[cfg_attr(, (cc))]
+   |                ^
+   |
+   = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute>
+help: must be of the form
+   |
+LL -     #[cfg_attr(, (cc))]
+LL +     #[cfg_attr(predicate, attr1, attr2, ...)]
+   |
+
+error: `#[inline]` attribute cannot be used on expressions
+  --> $DIR/cfg-attr-parsed-span-issue-154801.rs:9:5
+   |
+LL |     #[inline]
+   |     ^^^^^^^^^
+   |
+   = help: `#[inline]` can only be applied to functions
+
+error[E0308]: mismatched types
+  --> $DIR/cfg-attr-parsed-span-issue-154801.rs:4:5
+   |
+LL | fn main() {
+   |          - expected `()` because of default return type
+...
+LL |     _x
+   |     ^^ expected `()`, found integer
+
+error[E0308]: mismatched types
+  --> $DIR/cfg-attr-parsed-span-issue-154801.rs:10:5
+   |
+LL | fn inline_case() {
+   |                 - help: try adding a return type: `-> i32`
+...
+LL |     _x
+   |     ^^ expected `()`, found integer
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0308`.