Auto merge of #15006 - HKalbasi:format-panic, r=HKalbasi

Fix unwrap on None in expanding format args

fix #15002

Author: bors

crates/hir-def/src/macro_expansion_tests/builtin_fn_macro.rs

@@ -207,6 +207,44 @@ fn main() {
     );
 }
 
+#[test]
+fn regression_15002() {
+    check(
+        r#"
+#[rustc_builtin_macro]
+macro_rules! format_args {
+    ($fmt:expr) => ({ /* compiler built-in */ });
+    ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ })
+}
+
+fn main() {
+    format_args!(x = 2);
+    format_args!(x =);
+    format_args!(x =, x = 2);
+    format_args!("{}", x =);
+    format_args!(=, "{}", x =);
+    format_args!(x = 2, "{}", 5);
+}
+"#,
+        expect![[r##"
+#[rustc_builtin_macro]
+macro_rules! format_args {
+    ($fmt:expr) => ({ /* compiler built-in */ });
+    ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ })
+}
+
+fn main() {
+    /* error: no rule matches input tokens */;
+    /* error: no rule matches input tokens */;
+    /* error: no rule matches input tokens */;
+    /* error: no rule matches input tokens */::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::Argument::new(&(), ::core::fmt::Display::fmt), ]);
+    /* error: no rule matches input tokens */;
+    ::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::Argument::new(&(5), ::core::fmt::Display::fmt), ]);
+}
+"##]],
+    );
+}
+
 #[test]
 fn test_format_args_expand_with_comma_exprs() {
     check(

crates/hir-expand/src/builtin_fn_macro.rs

@@ -262,9 +262,6 @@ fn format_args_expand_general(
     let expand_error =
         ExpandResult::new(tt::Subtree::empty(), mbe::ExpandError::NoMatchingRule.into());
 
-    if args.is_empty() {
-        return expand_error;
-    }
     let mut key_args = FxHashMap::default();
     let mut args = args.into_iter().filter_map(|mut arg| {
         // Remove `key =`.
@@ -281,7 +278,9 @@ fn format_args_expand_general(
         Some(arg)
     }).collect::<Vec<_>>().into_iter();
     // ^^^^^^^ we need this collect, to enforce the side effect of the filter_map closure (building the `key_args`)
-    let format_subtree = args.next().unwrap();
+    let Some(format_subtree) = args.next() else {
+        return expand_error;
+    };
     let format_string = (|| {
         let token_tree = format_subtree.token_trees.get(0)?;
         match token_tree {