Expand relative assets to a placeholder if we are running in rust (#4860)

analyzer

packages/manganis/manganis-macro/src/lib.rs

@@ -209,6 +209,16 @@ fn resolve_path(raw: &str, span: Span) -> Result<PathBuf, AssetParseError> {
         if let Some(local_folder) = span.local_file().as_ref().and_then(|f| f.parent()) {
             local_folder.join(raw)
         } else {
+            // If we are running in rust analyzer, just assume the path is valid and return an error when
+            // we compile if it doesn't exist
+            if looks_like_rust_analyzer(&span) {
+                return Ok(
+                    "The asset macro was expanded under Rust Analyzer which doesn't support paths or local assets yet"
+                        .into(),
+                );
+            }
+
+            // Otherwise, return an error about the version of rust required for relative assets
             return Err(AssetParseError::RelativeAssetPath);
         }
     } else {
@@ -328,3 +338,22 @@ impl std::fmt::Display for AssetParseError {
         }
     }
 }
+
+/// Rust analyzer doesn't provide a stable way to detect if macros are running under it.
+/// This function uses heuristics to determine if we are running under rust analyzer for better error
+/// messages.
+fn looks_like_rust_analyzer(span: &Span) -> bool {
+    // Rust analyzer spans have a struct debug impl compared to rustcs custom debug impl
+    // RA Example: SpanData { range: 45..58, anchor: SpanAnchor(EditionedFileId(0, Edition2024), ErasedFileAstId { kind: Fn, index: 0, hash: 9CD8 }), ctx: SyntaxContext(4294967036) }
+    // Rustc Example: #0 bytes(70..83)
+    let looks_like_rust_analyzer_span = format!("{:?}", span).contains("ctx:");
+    // The rust analyzer macro expander runs under RUST_ANALYZER_INTERNALS_DO_NOT_USE
+    let looks_like_rust_analyzer_env = std::env::var("RUST_ANALYZER_INTERNALS_DO_NOT_USE").is_ok();
+    // The rust analyzer executable is named rust-analyzer-proc-macro-srv
+    let looks_like_rust_analyzer_exe = std::env::current_exe().ok().is_some_and(|p| {
+        p.file_stem()
+            .and_then(|s| s.to_str())
+            .is_some_and(|s| s.contains("rust-analyzer"))
+    });
+    looks_like_rust_analyzer_span || looks_like_rust_analyzer_env || looks_like_rust_analyzer_exe
+}