applying /Brepro in bootstrap on MSVC and adding a run-make test.

src/bootstrap/src/core/build_steps/compile.rs

@@ -1248,6 +1248,14 @@ pub fn rustc_cargo(
     // <https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Internal.20lint.20for.20raw.20.60print!.60.20and.20.60println!.60.3F>.
     cargo.rustflag("-Zon-broken-pipe=kill");
 
+    // /Brepro tells the MSVC linker to omit non-deterministic COFF data
+    // (namely the PE timestamp) from the produced binary. Only applied when
+    // building rustc itself via bootstrap. See discussion:
+    // https://github.com/rust-lang/rust/pull/158873
+    if target.is_msvc() {
+        cargo.rustflag("-Clink-arg=/Brepro");
+    }
+
     // Building with protected visibility reduces the number of dynamic relocations needed, giving
     // us a faster startup time. However GNU ld < 2.40 will error if we try to link a shared object
     // with direct references to protected symbols, so for now we only use protected symbols if

tests/run-make/brepro-msvc-determinism/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("brepro");
+}

tests/run-make/brepro-msvc-determinism/rmake.rs

@@ -0,0 +1,73 @@
+use std::path::PathBuf;
+
+use object::pod::slice_from_all_bytes;
+use object::read::pe::{ImageNtHeaders, PeFile, PeFile32, PeFile64};
+use object::{FileKind, Object, pe};
+use run_make_support::{bin_name, is_windows_msvc, object, rfs, rustc};
+
+// Returns the TimeDateStamp values from every IMAGE_DEBUG_DIRECTORY entry
+// in a parsed PE image.
+// Shared by both PE32 and PE32+ binaries.
+fn timestamps<Pe: ImageNtHeaders>(obj: &PeFile<'_, Pe>) -> Vec<u32> {
+    let data_dir =
+        obj.data_directory(pe::IMAGE_DIRECTORY_ENTRY_DEBUG).expect("no debug directory found");
+
+    let debug_data =
+        data_dir.data(obj.data(), &obj.section_table()).expect("failed to read debug directory");
+
+    let debug_dirs = slice_from_all_bytes::<pe::ImageDebugDirectory>(debug_data)
+        .expect("invalid IMAGE_DEBUG_DIRECTORY");
+
+    let mut stamps = Vec::new();
+
+    // COFF file header TimeDateStamp.
+    stamps.push(obj.nt_headers().file_header().time_date_stamp.get(object::LittleEndian));
+
+    // IMAGE_DEBUG_DIRECTORY TimeDateStamp values.
+    stamps.extend(debug_dirs.iter().map(|d| d.time_date_stamp.get(object::LittleEndian)));
+
+    stamps
+}
+
+fn main() {
+    if !is_windows_msvc() {
+        return;
+    }
+
+    // Compile the test crate and collect the
+    // IMAGE_DEBUG_DIRECTORY timestamps from the resulting executable.
+    let build = || -> Vec<u32> {
+        rustc().input("main.rs").arg("-Clink-arg=/Brepro").output(bin_name("brepro-test")).run();
+
+        let bytes = rfs::read(bin_name("brepro-test"));
+
+        // Parse the generated executable according to its PE format so the
+        // test works for both 32-bit and 64-bit MSVC targets.
+        match FileKind::parse(bytes.as_slice()).unwrap() {
+            FileKind::Pe32 => {
+                let obj = PeFile32::parse(bytes.as_slice()).unwrap();
+                timestamps(&obj)
+            }
+            FileKind::Pe64 => {
+                let obj = PeFile64::parse(bytes.as_slice()).unwrap();
+                timestamps(&obj)
+            }
+            kind => panic!("unexpected file kind: {kind:?}"),
+        }
+    };
+
+    // First build.
+    let stamps_a = build();
+
+    // Remove the generated PDB so the second build starts fresh.
+    rfs::remove_file(PathBuf::from(bin_name("brepro-test")).with_extension("pdb"));
+
+    // Second build.
+    let stamps_b = build();
+
+    assert!(!stamps_a.is_empty(), "no IMAGE_DEBUG_DIRECTORY entries found");
+
+    // /Brepro should make the linker emit deterministic timestamps across
+    // identical builds.
+    assert_eq!(stamps_a, stamps_b, "TimeDateStamp differs between identical builds");
+}