Add an error when full metadata was not found

compiler/rustc_metadata/messages.ftl

@@ -97,6 +97,10 @@ metadata_found_staticlib =
     found staticlib `{$crate_name}` instead of rlib or dylib{$add_info}
     .help = please recompile that crate using --crate-type lib
 
+metadata_full_metadata_not_found =
+    only metadata stub found for `{$flavor}` dependency `{$crate_name}`
+    please provide path to the corresponding .rmeta file with full metadata
+
 metadata_global_alloc_required =
     no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait
 

compiler/rustc_metadata/src/errors.rs

@@ -525,6 +525,15 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for MultipleCandidates {
     }
 }
 
+#[derive(Diagnostic)]
+#[diag(metadata_full_metadata_not_found)]
+pub(crate) struct FullMetadataNotFound {
+    #[primary_span]
+    pub span: Span,
+    pub flavor: CrateFlavor,
+    pub crate_name: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(metadata_symbol_conflicts_current, code = E0519)]
 pub struct SymbolConflictsCurrent {

compiler/rustc_metadata/src/locator.rs

@@ -654,7 +654,24 @@ impl<'a> CrateLocator<'a> {
                     continue;
                 }
             }
-            *slot = Some((hash, metadata, lib.clone()));
+
+            // We error eagerly here. If we're locating a rlib, then in theory the full metadata
+            // could still be in a (later resolved) dylib. In practice, if the rlib and dylib
+            // were produced in a way where one has full metadata and the other hasn't, it would
+            // mean that they were compiled using different compiler flags and probably also have
+            // a different SVH value.
+            if metadata.get_header().is_stub {
+                // `is_stub` should never be true for .rmeta files.
+                assert_ne!(flavor, CrateFlavor::Rmeta);
+
+                // Because rmeta files are resolved before rlib/dylib files, if this is a stub and
+                // we haven't found a slot already, it means that the full metadata is missing.
+                if slot.is_none() {
+                    return Err(CrateError::FullMetadataNotFound(self.crate_name, flavor));
+                }
+            } else {
+                *slot = Some((hash, metadata, lib.clone()));
+            }
             ret = Some((lib, kind));
         }
 
@@ -916,6 +933,7 @@ pub(crate) enum CrateError {
     ExternLocationNotExist(Symbol, PathBuf),
     ExternLocationNotFile(Symbol, PathBuf),
     MultipleCandidates(Symbol, CrateFlavor, Vec<PathBuf>),
+    FullMetadataNotFound(Symbol, CrateFlavor),
     SymbolConflictsCurrent(Symbol),
     StableCrateIdCollision(Symbol, Symbol),
     DlOpen(String, String),
@@ -966,6 +984,9 @@ impl CrateError {
             CrateError::MultipleCandidates(crate_name, flavor, candidates) => {
                 dcx.emit_err(errors::MultipleCandidates { span, crate_name, flavor, candidates });
             }
+            CrateError::FullMetadataNotFound(crate_name, flavor) => {
+                dcx.emit_err(errors::FullMetadataNotFound { span, crate_name, flavor });
+            }
             CrateError::SymbolConflictsCurrent(root_name) => {
                 dcx.emit_err(errors::SymbolConflictsCurrent { span, crate_name: root_name });
             }