Improve debugging for metadata structures

I had to do a lot of debug by printing; having these `Debug` traits in
place made it easier. Additionally, add some more information to
existing `info!` statements.

compiler/rustc_metadata/src/creader.rs

@@ -147,6 +147,7 @@ impl<'a> std::fmt::Debug for CrateDump<'a> {
             writeln!(fmt, "  cnum: {cnum}")?;
             writeln!(fmt, "  hash: {}", data.hash())?;
             writeln!(fmt, "  reqd: {:?}", data.dep_kind())?;
+            writeln!(fmt, "  priv: {:?}", data.is_private_dep())?;
             let CrateSource { dylib, rlib, rmeta } = data.source();
             if let Some(dylib) = dylib {
                 writeln!(fmt, "  dylib: {}", dylib.0.display())?;
@@ -770,7 +771,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
 
         match result {
             (LoadResult::Previous(cnum), None) => {
-                info!("library for `{}` was loaded previously", name);
+                info!("library for `{}` was loaded previously, cnum {cnum}", name);
                 // When `private_dep` is none, it indicates the directly dependent crate. If it is
                 // not specified by `--extern` on command line parameters, it may be
                 // `private-dependency` when `register_crate` is called for the first time. Then it must be updated to

compiler/rustc_metadata/src/locator.rs

@@ -260,7 +260,7 @@ pub(crate) struct CrateLocator<'a> {
     crate_rejections: CrateRejections,
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub(crate) struct CratePaths {
     pub(crate) name: Symbol,
     source: CrateSource,
@@ -272,7 +272,7 @@ impl CratePaths {
     }
 }
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub(crate) enum CrateFlavor {
     Rlib,
     Rmeta,
@@ -893,13 +893,13 @@ fn get_flavor_from_path(path: &Path) -> CrateFlavor {
 
 // ------------------------------------------ Error reporting -------------------------------------
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 struct CrateMismatch {
     path: PathBuf,
     got: String,
 }
 
-#[derive(Clone, Default)]
+#[derive(Clone, Debug, Default)]
 struct CrateRejections {
     via_hash: Vec<CrateMismatch>,
     via_triple: Vec<CrateMismatch>,
@@ -912,6 +912,7 @@ struct CrateRejections {
 /// Candidate rejection reasons collected during crate search.
 /// If no candidate is accepted, then these reasons are presented to the user,
 /// otherwise they are ignored.
+#[derive(Debug)]
 pub(crate) struct CombinedLocatorError {
     crate_name: Symbol,
     dep_root: Option<CratePaths>,
@@ -921,6 +922,7 @@ pub(crate) struct CombinedLocatorError {
     crate_rejections: CrateRejections,
 }
 
+#[derive(Debug)]
 pub(crate) enum CrateError {
     NonAsciiName(Symbol),
     ExternLocationNotExist(Symbol, PathBuf),

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1936,6 +1936,10 @@ impl CrateMetadata {
         self.root.needs_panic_runtime
     }
 
+    pub(crate) fn is_private_dep(&self) -> bool {
+        self.private_dep
+    }
+
     pub(crate) fn is_panic_runtime(&self) -> bool {
         self.root.panic_runtime
     }