Replace spaghetti with a simple errors enum

compiler/rustc_driver/src/lib.rs

@@ -18,7 +18,7 @@ extern crate tracing;
 pub extern crate rustc_plugin_impl as plugin;
 
 use rustc_ast as ast;
-use rustc_codegen_ssa::{traits::CodegenBackend, CodegenResults};
+use rustc_codegen_ssa::{traits::CodegenBackend, CodegenErrors, CodegenResults};
 use rustc_data_structures::profiling::{get_resident_set_size, print_time_passes_entry};
 use rustc_data_structures::sync::SeqCst;
 use rustc_errors::registry::{InvalidErrorCode, Registry};
@@ -60,7 +60,10 @@ pub mod args;
 pub mod pretty;
 mod session_diagnostics;
 
-use crate::session_diagnostics::{RlinkNotAFile, RlinkUnableToDeserialize, RlinkUnableToRead};
+use crate::session_diagnostics::{
+    RLinkEmptyVersionNumber, RLinkEncodingVersionMismatch, RLinkRustcVersionMismatch,
+    RLinkWrongFileType, RlinkNotAFile, RlinkUnableToRead,
+};
 
 /// Exit status code used for successful compilation and help output.
 pub const EXIT_SUCCESS: i32 = 0;
@@ -591,7 +594,24 @@ pub fn try_process_rlink(sess: &Session, compiler: &interface::Compiler) -> Comp
             let codegen_results = match CodegenResults::deserialize_rlink(rlink_data) {
                 Ok(codegen) => codegen,
                 Err(err) => {
-                    sess.emit_fatal(RlinkUnableToDeserialize { err });
+                    match err {
+                        CodegenErrors::WrongFileType => sess.emit_fatal(RLinkWrongFileType),
+                        CodegenErrors::EmptyVersionNumber => {
+                            sess.emit_fatal(RLinkEmptyVersionNumber)
+                        }
+                        CodegenErrors::EncodingVersionMismatch { version_array, rlink_version } => {
+                            sess.emit_fatal(RLinkEncodingVersionMismatch {
+                                version_array,
+                                rlink_version,
+                            })
+                        }
+                        CodegenErrors::RustcVersionMismatch { rustc_version, current_version } => {
+                            sess.emit_fatal(RLinkRustcVersionMismatch {
+                                rustc_version,
+                                current_version,
+                            })
+                        }
+                    };
                 }
             };
             let result = compiler.codegen_backend().link(sess, codegen_results, &outputs);

compiler/rustc_driver/src/session_diagnostics.rs

@@ -1,4 +1,3 @@
-use rustc_codegen_ssa::session_diagnostic::DeserializeRlinkError;
 use rustc_macros::SessionDiagnostic;
 
 #[derive(SessionDiagnostic)]
@@ -8,9 +7,25 @@ pub(crate) struct RlinkUnableToRead {
 }
 
 #[derive(SessionDiagnostic)]
-#[diag(driver::rlink_unable_to_deserialize)]
-pub(crate) struct RlinkUnableToDeserialize {
-    pub err: DeserializeRlinkError,
+#[diag(driver::rlink_wrong_file_type)]
+pub(crate) struct RLinkWrongFileType;
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_empty_version_number)]
+pub(crate) struct RLinkEmptyVersionNumber;
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_encoding_version_mismatch)]
+pub(crate) struct RLinkEncodingVersionMismatch {
+    pub version_array: String,
+    pub rlink_version: String,
+}
+
+#[derive(SessionDiagnostic)]
+#[diag(driver::rlink_rustc_version_mismatch)]
+pub(crate) struct RLinkRustcVersionMismatch {
+    pub rustc_version: String,
+    pub current_version: String,
 }
 
 #[derive(SessionDiagnostic)]