linker: Fix escaping style for response files on Windows

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1726,8 +1726,12 @@ fn exec_linker(
         args.push_str(
             &Escape {
                 arg: arg.to_str().unwrap(),
-                // LLD also uses MSVC-like parsing for @-files by default when running on windows hosts
-                is_like_msvc: sess.target.is_like_msvc || (cfg!(windows) && flavor.uses_lld()),
+                // Windows-style escaping for @-files is used by
+                // - all linkers targeting MSVC-like targets, including LLD
+                // - all LLD flavors running on Windows hosts
+                // С/С++ compilers use Posix-style escaping (except clang-cl, which we do not use).
+                is_like_msvc: sess.target.is_like_msvc
+                    || (cfg!(windows) && flavor.uses_lld() && !flavor.uses_cc()),
             }
             .to_string(),
         );

src/bootstrap/src/core/build_steps/test.rs

@@ -269,7 +269,13 @@ impl Step for Cargotest {
             .args(builder.config.test_args())
             .env("RUSTC", builder.rustc(compiler))
             .env("RUSTDOC", builder.rustdoc(compiler));
-        add_rustdoc_cargo_linker_args(&mut cmd, builder, compiler.host, LldThreads::No);
+        add_rustdoc_cargo_linker_args(
+            &mut cmd,
+            builder,
+            compiler.host,
+            LldThreads::No,
+            compiler.stage,
+        );
         cmd.delay_failure().run(builder);
     }
 }
@@ -847,7 +853,7 @@ impl Step for RustdocTheme {
             .env("CFG_RELEASE_CHANNEL", &builder.config.channel)
             .env("RUSTDOC_REAL", builder.rustdoc(self.compiler))
             .env("RUSTC_BOOTSTRAP", "1");
-        cmd.args(linker_args(builder, self.compiler.host, LldThreads::No));
+        cmd.args(linker_args(builder, self.compiler.host, LldThreads::No, self.compiler.stage));
 
         cmd.delay_failure().run(builder);
     }
@@ -1023,7 +1029,13 @@ impl Step for RustdocGUI {
         cmd.env("RUSTDOC", builder.rustdoc(self.compiler))
             .env("RUSTC", builder.rustc(self.compiler));
 
-        add_rustdoc_cargo_linker_args(&mut cmd, builder, self.compiler.host, LldThreads::No);
+        add_rustdoc_cargo_linker_args(
+            &mut cmd,
+            builder,
+            self.compiler.host,
+            LldThreads::No,
+            self.compiler.stage,
+        );
 
         for path in &builder.paths {
             if let Some(p) = helpers::is_valid_test_suite_arg(path, "tests/rustdoc-gui", builder) {
@@ -1883,7 +1895,7 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
 
         let mut hostflags = flags.clone();
         hostflags.push(format!("-Lnative={}", builder.test_helpers_out(compiler.host).display()));
-        hostflags.extend(linker_flags(builder, compiler.host, LldThreads::No));
+        hostflags.extend(linker_flags(builder, compiler.host, LldThreads::No, compiler.stage));
 
         let mut targetflags = flags;
         targetflags.push(format!("-Lnative={}", builder.test_helpers_out(target).display()));

src/bootstrap/src/core/builder/cargo.rs

@@ -260,7 +260,7 @@ impl Cargo {
             }
         }
 
-        for arg in linker_args(builder, compiler.host, LldThreads::Yes) {
+        for arg in linker_args(builder, compiler.host, LldThreads::Yes, 0) {
             self.hostflags.arg(&arg);
         }
 
@@ -270,10 +270,10 @@ impl Cargo {
         }
         // We want to set -Clinker using Cargo, therefore we only call `linker_flags` and not
         // `linker_args` here.
-        for flag in linker_flags(builder, target, LldThreads::Yes) {
+        for flag in linker_flags(builder, target, LldThreads::Yes, compiler.stage) {
             self.rustflags.arg(&flag);
         }
-        for arg in linker_args(builder, target, LldThreads::Yes) {
+        for arg in linker_args(builder, target, LldThreads::Yes, compiler.stage) {
             self.rustdocflags.arg(&arg);
         }
 

src/bootstrap/src/core/builder/mod.rs

@@ -1462,7 +1462,7 @@ impl<'a> Builder<'a> {
             cmd.arg("-Dwarnings");
         }
         cmd.arg("-Znormalize-docs");
-        cmd.args(linker_args(self, compiler.host, LldThreads::Yes));
+        cmd.args(linker_args(self, compiler.host, LldThreads::Yes, compiler.stage));
         cmd
     }
 

src/bootstrap/src/utils/helpers.rs

@@ -430,8 +430,9 @@ pub fn linker_args(
     builder: &Builder<'_>,
     target: TargetSelection,
     lld_threads: LldThreads,
+    stage: u32,
 ) -> Vec<String> {
-    let mut args = linker_flags(builder, target, lld_threads);
+    let mut args = linker_flags(builder, target, lld_threads, stage);
 
     if let Some(linker) = builder.linker(target) {
         args.push(format!("-Clinker={}", linker.display()));
@@ -446,12 +447,18 @@ pub fn linker_flags(
     builder: &Builder<'_>,
     target: TargetSelection,
     lld_threads: LldThreads,
+    stage: u32,
 ) -> Vec<String> {
     let mut args = vec![];
     if !builder.is_lld_direct_linker(target) && builder.config.lld_mode.is_used() {
         match builder.config.lld_mode {
             LldMode::External => {
-                args.push("-Clinker-flavor=gnu-lld-cc".to_string());
+                // cfg(bootstrap) - remove after updating bootstrap compiler (#137498)
+                if stage == 0 && target.is_windows() {
+                    args.push("-Clink-arg=-fuse-ld=lld".to_string());
+                } else {
+                    args.push("-Clinker-flavor=gnu-lld-cc".to_string());
+                }
                 // FIXME(kobzol): remove this flag once MCP510 gets stabilized
                 args.push("-Zunstable-options".to_string());
             }
@@ -479,8 +486,9 @@ pub fn add_rustdoc_cargo_linker_args(
     builder: &Builder<'_>,
     target: TargetSelection,
     lld_threads: LldThreads,
+    stage: u32,
 ) {
-    let args = linker_args(builder, target, lld_threads);
+    let args = linker_args(builder, target, lld_threads, stage);
     let mut flags = cmd
         .get_envs()
         .find_map(|(k, v)| if k == OsStr::new("RUSTDOCFLAGS") { v } else { None })