Fix ICE from cfg_attr_trace by storing span

Author: chenyukang

compiler/rustc_attr_parsing/src/early_parsed.rs

@@ -18,9 +18,10 @@ pub(crate) struct EarlyParsedState {
     cfg_trace: ThinVec<(CfgEntry, Span)>,
 
     /// Attribute state for `#[cfg_attr]` trace attributes
-    /// The arguments of these attributes is no longer relevant for any later passes, only their presence.
-    /// So we discard the arguments here.
-    cfg_attr_trace: bool,
+    /// The arguments of these attributes are no longer relevant for later passes,
+    /// but we still keep a source span so downstream diagnostics can tell that the
+    /// original expression had a prefix attribute.
+    cfg_attr_trace: Option<Span>,
 }
 
 impl EarlyParsedState {
@@ -37,7 +38,7 @@ impl EarlyParsedState {
                 self.cfg_trace.push((cfg, attr_span));
             }
             EarlyParsedAttribute::CfgAttrTrace => {
-                self.cfg_attr_trace = true;
+                self.cfg_attr_trace.get_or_insert(attr_span);
             }
         }
     }
@@ -46,8 +47,8 @@ impl EarlyParsedState {
         if !self.cfg_trace.is_empty() {
             attributes.push(Attribute::Parsed(AttributeKind::CfgTrace(self.cfg_trace)));
         }
-        if self.cfg_attr_trace {
-            attributes.push(Attribute::Parsed(AttributeKind::CfgAttrTrace));
+        if let Some(span) = self.cfg_attr_trace {
+            attributes.push(Attribute::Parsed(AttributeKind::CfgAttrTrace(span)));
         }
     }
 }

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1095,7 +1095,7 @@ pub enum AttributeKind {
     AutomaticallyDerived(Span),
 
     /// Represents the trace attribute of `#[cfg_attr]`
-    CfgAttrTrace,
+    CfgAttrTrace(Span),
 
     /// Represents the trace attribute of `#[cfg]`
     CfgTrace(ThinVec<(CfgEntry, Span)>),

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -21,7 +21,7 @@ impl AttributeKind {
             AllowInternalUnsafe(..) => Yes,
             AllowInternalUnstable(..) => Yes,
             AutomaticallyDerived(..) => Yes,
-            CfgAttrTrace => Yes,
+            CfgAttrTrace(..) => Yes,
             CfgTrace(..) => Yes,
             CfiEncoding { .. } => Yes,
             Cold(..) => No,

compiler/rustc_hir/src/hir.rs

@@ -1308,6 +1308,7 @@ impl Attribute {
     pub fn has_span_without_desugaring_kind(&self) -> bool {
         let span = match self {
             Attribute::Unparsed(attr) => attr.span,
+            Attribute::Parsed(AttributeKind::CfgAttrTrace(span)) => *span,
             Attribute::Parsed(AttributeKind::Deprecated { span, .. }) => *span,
             Attribute::Parsed(AttributeKind::LintAttributes(sub_attrs)) => {
                 return sub_attrs.iter().any(|attr| attr.attr_span.desugaring_kind().is_none());

compiler/rustc_passes/src/check_attr.rs

@@ -226,7 +226,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     // tidy-alphabetical-start
                     AttributeKind::RustcAllowIncoherentImpl(..)
                     | AttributeKind::AutomaticallyDerived(..)
-                    | AttributeKind::CfgAttrTrace
+                    | AttributeKind::CfgAttrTrace(..)
                     | AttributeKind::CfgTrace(..)
                     | AttributeKind::CfiEncoding { .. }
                     | AttributeKind::Cold(..)

src/tools/clippy/clippy_lints/src/incompatible_msrv.rs

@@ -269,5 +269,5 @@ impl<'tcx> LateLintPass<'tcx> for IncompatibleMsrv {
 fn is_under_cfg_attribute(cx: &LateContext<'_>, hir_id: HirId) -> bool {
     cx.tcx
         .hir_parent_id_iter(hir_id)
-        .any(|id| find_attr!(cx.tcx, id, CfgTrace(..) | CfgAttrTrace))
+        .any(|id| find_attr!(cx.tcx, id, CfgTrace(..) | CfgAttrTrace(..)))
 }

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

@@ -0,0 +1,5 @@
+fn main() {
+    let _x = 30;
+    #[cfg_attr(, (cc))] //~ ERROR expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found `,`
+    _x //~ ERROR mismatched types
+}

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

@@ -0,0 +1,20 @@
+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))]
+   |     -----------^------- help: must be of the form: `#[cfg_attr(predicate, attr1, attr2, ...)]`
+   |
+   = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute>
+
+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: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.