Remove `CodegenBackend::target_override`.

Backend and target selection is a mess: the target can override the
backend (via `Target::default_codegen_backend`), *and* the backend can
override the target (via `CodegenBackend::target_override`).

The code that handles this is ugly. It calls `build_target_config`
twice, once before getting the backend and once again afterward. It also
must check that both overrides aren't triggering at the same time.

This commit removes the latter override. It's used in rust-gpu but
@eddyb said via Zulip that removing it would be ok. This simplifies the
code greatly, and will allow some nice follow-up refactorings.

1 files changed, 18 insertions, 27 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index e6eb1a3e83c..a88ae268e27 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -22,7 +22,7 @@ use rustc_span::{FileName, FileNameDisplayPreference, RealFileName, SourceFileHa
 use rustc_target::abi::Align;
 use rustc_target::spec::LinkSelfContainedComponents;
 use rustc_target::spec::{PanicStrategy, RelocModel, SanitizerSet, SplitDebuginfo};
-use rustc_target::spec::{Target, TargetTriple, TargetWarnings, TARGETS};
+use rustc_target::spec::{Target, TargetTriple, TARGETS};
 use std::collections::btree_map::{
     Iter as BTreeMapIter, Keys as BTreeMapKeysIter, Values as BTreeMapValuesIter,
 };
@@ -1549,34 +1549,25 @@ pub fn build_configuration(sess: &Session, mut user_cfg: Cfg) -> Cfg {
     user_cfg
 }
 
-pub fn build_target_config(
-    early_dcx: &EarlyDiagCtxt,
-    opts: &Options,
-    target_override: Option<Target>,
-    sysroot: &Path,
-) -> Target {
-    let target_result = target_override.map_or_else(
-        || Target::search(&opts.target_triple, sysroot),
-        |t| Ok((t, TargetWarnings::empty())),
-    );
-    let (target, target_warnings) = target_result.unwrap_or_else(|e| {
-        early_dcx.early_fatal(format!(
+pub fn build_target_config(early_dcx: &EarlyDiagCtxt, opts: &Options, sysroot: &Path) -> Target {
+    match Target::search(&opts.target_triple, sysroot) {
+        Ok((target, warnings)) => {
+            for warning in warnings.warning_messages() {
+                early_dcx.early_warn(warning)
+            }
+            if !matches!(target.pointer_width, 16 | 32 | 64) {
+                early_dcx.early_fatal(format!(
+                    "target specification was invalid: unrecognized target-pointer-width {}",
+                    target.pointer_width
+                ))
+            }
+            target
+        }
+        Err(e) => early_dcx.early_fatal(format!(
             "Error loading target specification: {e}. \
-                 Run `rustc --print target-list` for a list of built-in targets"
-        ))
-    });
-    for warning in target_warnings.warning_messages() {
-        early_dcx.early_warn(warning)
-    }
-
-    if !matches!(target.pointer_width, 16 | 32 | 64) {
-        early_dcx.early_fatal(format!(
-            "target specification was invalid: unrecognized target-pointer-width {}",
-            target.pointer_width
-        ))
+                     Run `rustc --print target-list` for a list of built-in targets"
+        )),
     }
-
-    target
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]