2 files changed, 20 insertions, 1 deletions

diff --git a/crates/ra_hir_expand/src/builtin_macro.rs b/crates/ra_hir_expand/src/builtin_macro.rs
index 35f99b2bc..e0709704a 100644
--- a/crates/ra_hir_expand/src/builtin_macro.rs
+++ b/crates/ra_hir_expand/src/builtin_macro.rs
@@ -49,7 +49,11 @@ register_builtin! {
     (COMPILE_ERROR_MACRO, CompileError) => compile_error_expand,
     (FILE_MACRO, File) => file_expand,
     (LINE_MACRO, Line) => line_expand,
-    (STRINGIFY_MACRO, Stringify) => stringify_expand
+    (STRINGIFY_MACRO, Stringify) => stringify_expand,
+    (FORMAT_ARGS_MACRO, FormatArgs) => format_args_expand,
+    // format_args_nl only differs in that it adds a newline in the end,
+    // so we use the same stub expansion for now
+    (FORMAT_ARGS_NL_MACRO, FormatArgsNl) => format_args_expand
 }
 
 fn to_line_number(db: &dyn AstDatabase, file: HirFileId, pos: TextUnit) -> usize {
@@ -200,6 +204,19 @@ fn compile_error_expand(
     Err(mbe::ExpandError::BindingError("Must be a string".into()))
 }
 
+fn format_args_expand(
+    _db: &dyn AstDatabase,
+    _id: MacroCallId,
+    _tt: &tt::Subtree,
+) -> Result<tt::Subtree, mbe::ExpandError> {
+    // FIXME this is just a stub to make format macros type-check without mismatches
+    // We should make this at least insert the arguments, so that go to def etc. work within format macros
+    let expanded = quote! {
+        std::fmt::Arguments::new_v1(&[], &[])
+    };
+    Ok(expanded)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/crates/ra_hir_expand/src/name.rs b/crates/ra_hir_expand/src/name.rs
index c5a191160..34edf2003 100644
--- a/crates/ra_hir_expand/src/name.rs
+++ b/crates/ra_hir_expand/src/name.rs
@@ -159,6 +159,8 @@ pub const COLUMN_MACRO: Name = Name::new_inline_ascii(6, b"column");
 pub const COMPILE_ERROR_MACRO: Name = Name::new_inline_ascii(13, b"compile_error");
 pub const LINE_MACRO: Name = Name::new_inline_ascii(4, b"line");
 pub const STRINGIFY_MACRO: Name = Name::new_inline_ascii(9, b"stringify");
+pub const FORMAT_ARGS_MACRO: Name = Name::new_inline_ascii(11, b"format_args");
+pub const FORMAT_ARGS_NL_MACRO: Name = Name::new_inline_ascii(14, b"format_args_nl");
 
 // Builtin derives
 pub const COPY_TRAIT: Name = Name::new_inline_ascii(4, b"Copy");