Auto merge of #17936 - Veykril:module_path, r=Veykril

feat: Implement `module_path` macro

Turns out this is a pain to implement because of our hir-def hir-expand split :)

crates/hir-expand/src/builtin.rs

@@ -1,6 +1,6 @@
 //! Builtin macros and attributes
 #[macro_use]
-mod quote;
+pub(crate) mod quote;
 
 mod attr_macro;
 mod derive_macro;

crates/hir-expand/src/builtin/fn_macro.rs

@@ -116,7 +116,6 @@ register_builtin! {
     (column, Column) => line_expand,
     (file, File) => file_expand,
     (line, Line) => line_expand,
-    (module_path, ModulePath) => module_path_expand,
     (assert, Assert) => assert_expand,
     (stringify, Stringify) => stringify_expand,
     (llvm_asm, LlvmAsm) => asm_expand,
@@ -142,7 +141,10 @@ register_builtin! {
     (include_bytes, IncludeBytes) => include_bytes_expand,
     (include_str, IncludeStr) => include_str_expand,
     (env, Env) => env_expand,
-    (option_env, OptionEnv) => option_env_expand
+    (option_env, OptionEnv) => option_env_expand,
+    // This isn't really eager, we have no inputs, but we abuse the fact how eager macros are
+    // handled in r-a to be able to thread the module path through.
+    (module_path, ModulePath) => module_path_expand
 }
 
 fn mk_pound(span: Span) -> tt::Subtree {
@@ -157,18 +159,6 @@ fn mk_pound(span: Span) -> tt::Subtree {
     )
 }
 
-fn module_path_expand(
-    _db: &dyn ExpandDatabase,
-    _id: MacroCallId,
-    _tt: &tt::Subtree,
-    span: Span,
-) -> ExpandResult<tt::Subtree> {
-    // Just return a dummy result.
-    ExpandResult::ok(quote! {span =>
-         "module::path"
-    })
-}
-
 fn line_expand(
     _db: &dyn ExpandDatabase,
     _id: MacroCallId,
@@ -904,6 +894,18 @@ fn option_env_expand(
     ExpandResult::ok(expanded)
 }
 
+fn module_path_expand(
+    _db: &dyn ExpandDatabase,
+    _id: MacroCallId,
+    tt: &tt::Subtree,
+    span: Span,
+) -> ExpandResult<tt::Subtree> {
+    // Note: The actual implementation of this is in crates\hir-expand\src\eager.rs
+    ExpandResult::ok(quote! {span =>
+         #tt
+    })
+}
+
 fn quote_expand(
     _db: &dyn ExpandDatabase,
     _arg_id: MacroCallId,

crates/hir-expand/src/builtin/quote.rs

@@ -128,7 +128,7 @@ macro_rules! quote_impl__ {
         }
     };
 }
-pub(super) use quote_impl__ as __quote;
+pub(crate) use quote_impl__ as __quote;
 
 /// FIXME:
 /// It probably should implement in proc-macro
@@ -137,7 +137,7 @@ macro_rules! quote_impl {
         $crate::builtin::quote::IntoTt::to_subtree($crate::builtin::quote::__quote!($span $($tt)*), $span)
     }
 }
-pub(super) use quote_impl as quote;
+pub(crate) use quote_impl as quote;
 
 pub(crate) trait IntoTt {
     fn to_subtree(self, span: Span) -> crate::tt::Subtree;

crates/hir-expand/src/eager.rs

@@ -32,6 +32,51 @@ use crate::{
     MacroCallId, MacroCallKind, MacroCallLoc, MacroDefId, MacroDefKind,
 };
 
+pub fn expand_module_path_as_eager(
+    db: &dyn ExpandDatabase,
+    krate: CrateId,
+    mod_path: String,
+    macro_call: &ast::MacroCall,
+    ast_id: AstId<ast::MacroCall>,
+    def: MacroDefId,
+    call_site: SyntaxContextId,
+) -> ExpandResult<Option<MacroCallId>> {
+    let expand_to = ExpandTo::from_call_site(macro_call);
+
+    // Note:
+    // When `lazy_expand` is called, its *parent* file must already exist.
+    // Here we store an eager macro id for the argument expanded subtree
+    // for that purpose.
+    let arg_id = MacroCallLoc {
+        def,
+        krate,
+        kind: MacroCallKind::FnLike { ast_id, expand_to: ExpandTo::Expr, eager: None },
+        ctxt: call_site,
+    }
+    .intern(db);
+    #[allow(deprecated)] // builtin eager macros are never derives
+    let (_, _, span) = db.macro_arg(arg_id);
+    let subtree = crate::builtin::quote::quote! {span => #mod_path};
+
+    let loc = MacroCallLoc {
+        def,
+        krate,
+        kind: MacroCallKind::FnLike {
+            ast_id,
+            expand_to,
+            eager: Some(Arc::new(EagerCallInfo {
+                arg: Arc::new(subtree),
+                arg_id,
+                error: None,
+                span,
+            })),
+        },
+        ctxt: call_site,
+    };
+
+    ExpandResult { value: Some(loc.intern(db)), err: None }
+}
+
 pub fn expand_eager_macro_input(
     db: &dyn ExpandDatabase,
     krate: CrateId,