accept cfg on the first template

Author: folkertdev

compiler/rustc_builtin_macros/src/asm.rs

@@ -140,8 +140,23 @@ pub fn parse_asm_args<'a>(
         return Err(dcx.create_err(errors::AsmRequiresTemplate { span: sp }));
     }
 
-    let _attributes = AsmAttrVec::parse(ecx, p)?;
-    let first_template = p.parse_expr()?;
+    let first_template = loop {
+        let attributes = AsmAttrVec::parse(ecx, p)?;
+        let is_configured_out =
+            ecx.ecfg.features.asm_cfg() && strip_unconfigured.configure(attributes).is_none();
+
+        let template = p.parse_expr()?;
+
+        if !is_configured_out {
+            break template;
+        }
+
+        if !p.eat(exp!(Comma)) {
+            // After a template string, we always expect *only* a comma...
+            return Err(dcx.create_err(errors::AsmExpectedComma { span: p.token.span }));
+        }
+    };
+
     let mut args = AsmArgs {
         templates: vec![first_template],
         operands: vec![],

tests/ui/asm/cfg.rs

@@ -83,18 +83,32 @@ fn template_allowed() {
     }
 }
 
+#[unsafe(naked)]
+extern "C" fn first_template() -> u64 {
+    naked_asm!(
+        #[cfg(reva)]
+        "mov rax, 5",
+        #[cfg(revb)]
+        "mov rax, 10",
+        "ret",
+    )
+}
+
 pub fn main() {
     std::cfg_match! {
         reva => {
             assert_eq!(const_operand(), 5);
             assert_eq!(ignore_const_operand_cfg_attr(), 5);
             assert_eq!(ignore_const_operand(), 5);
+            assert_eq!(first_template(), 5);
 
         }
         revb => {
             assert_eq!(const_operand(), 10);
             assert_eq!(ignore_const_operand_cfg_attr(), 10);
             assert_eq!(ignore_const_operand(), 10);
+            assert_eq!(first_template(), 10);
+
         }
     }
     options();