Auto merge of #18131 - ChayimFriedman2:macro-expand-dollar-crate, r=Veykril

fix: Get rid of `$crate` in expansions shown to the user

Be it "Expand Macro Recursively", "Inline macro" or few other things.

We replace it with the crate name, as should've always been.

Probably fixes some issues, but I don't know what they are.

crates/hir-expand/src/lib.rs

@@ -21,6 +21,7 @@ pub mod span_map;
 
 mod cfg_process;
 mod fixup;
+mod prettify_macro_expansion_;
 
 use attrs::collect_attrs;
 use rustc_hash::FxHashMap;
@@ -51,11 +52,13 @@ use crate::{
     span_map::{ExpansionSpanMap, SpanMap},
 };
 
-pub use crate::files::{AstId, ErasedAstId, FileRange, InFile, InMacroFile, InRealFile};
+pub use crate::{
+    files::{AstId, ErasedAstId, FileRange, InFile, InMacroFile, InRealFile},
+    prettify_macro_expansion_::prettify_macro_expansion,
+};
 
 pub use mbe::{DeclarativeMacro, ValueResult};
 pub use span::{HirFileId, MacroCallId, MacroFileId};
-pub use syntax_bridge::insert_whitespace_into_node;
 
 pub mod tt {
     pub use span::Span;

crates/hir-expand/src/prettify_macro_expansion_.rs

@@ -0,0 +1,60 @@
+//! Pretty printing of macros output.
+
+use base_db::CrateId;
+use rustc_hash::FxHashMap;
+use syntax::NodeOrToken;
+use syntax::{ast::make, SyntaxNode};
+
+use crate::{db::ExpandDatabase, span_map::ExpansionSpanMap};
+
+/// Inserts whitespace and replaces `$crate` in macro expansions.
+#[expect(deprecated)]
+pub fn prettify_macro_expansion(
+    db: &dyn ExpandDatabase,
+    syn: SyntaxNode,
+    span_map: &ExpansionSpanMap,
+    target_crate_id: CrateId,
+) -> SyntaxNode {
+    let crate_graph = db.crate_graph();
+    let target_crate = &crate_graph[target_crate_id];
+    let mut syntax_ctx_id_to_dollar_crate_replacement = FxHashMap::default();
+    syntax_bridge::prettify_macro_expansion::prettify_macro_expansion(syn, &mut |dollar_crate| {
+        let ctx = span_map.span_at(dollar_crate.text_range().start()).ctx;
+        let replacement =
+            syntax_ctx_id_to_dollar_crate_replacement.entry(ctx).or_insert_with(|| {
+                let ctx_data = db.lookup_intern_syntax_context(ctx);
+                let macro_call_id =
+                    ctx_data.outer_expn.expect("`$crate` cannot come from `SyntaxContextId::ROOT`");
+                let macro_call = db.lookup_intern_macro_call(macro_call_id);
+                let macro_def_crate = macro_call.def.krate;
+                // First, if this is the same crate as the macro, nothing will work but `crate`.
+                // If not, if the target trait has the macro's crate as a dependency, using the dependency name
+                // will work in inserted code and match the user's expectation.
+                // If not, the crate's display name is what the dependency name is likely to be once such dependency
+                // is inserted, and also understandable to the user.
+                // Lastly, if nothing else found, resort to leaving `$crate`.
+                if target_crate_id == macro_def_crate {
+                    make::tokens::crate_kw()
+                } else if let Some(dep) =
+                    target_crate.dependencies.iter().find(|dep| dep.crate_id == macro_def_crate)
+                {
+                    make::tokens::ident(&dep.name)
+                } else if let Some(crate_name) = &crate_graph[macro_def_crate].display_name {
+                    make::tokens::ident(crate_name.crate_name())
+                } else {
+                    return dollar_crate.clone();
+                }
+            });
+        if replacement.text() == "$crate" {
+            // The parent may have many children, and looking for the token may yield incorrect results.
+            return dollar_crate.clone();
+        }
+        // We need to `clone_subtree()` but rowan doesn't provide such operation for tokens.
+        let parent = replacement.parent().unwrap().clone_subtree().clone_for_update();
+        parent
+            .children_with_tokens()
+            .filter_map(NodeOrToken::into_token)
+            .find(|it| it.kind() == replacement.kind())
+            .unwrap()
+    })
+}