Update /NODEFAUTLIB comment for msvc

ChrisDenton · ChrisDenton · commit aeec0d1269ee · 2024-03-11T18:31:50.000Z
diff --git a/compiler/rustc_target/src/spec/base/windows_msvc.rs b/compiler/rustc_target/src/spec/base/windows_msvc.rs
@@ -17,15 +17,19 @@ pub fn opts() -> TargetOptions {
         crt_static_allows_dylibs: true,
         crt_static_respected: true,
         requires_uwtable: true,
-        // Currently we don't pass the /NODEFAULTLIB flag to the linker on MSVC
-        // as there's been trouble in the past of linking the C++ standard
-        // library required by LLVM. This likely needs to happen one day, but
-        // in general Windows is also a more controlled environment than
-        // Unix, so it's not necessarily as critical that this be implemented.
+        // We don't pass the /NODEFAULTLIB flag to the linker on MSVC
+        // as that prevents linker directives embedded in object files from
+        // including other necessary libraries.
         //
-        // Note that there are also some licensing worries about statically
-        // linking some libraries which require a specific agreement, so it may
-        // not ever be possible for us to pass this flag.
+        // For example, msvcrt.lib embeds a linker directive like:
+        //    /DEFAULTLIB:vcruntime.lib /DEFAULTLIB:ucrt.lib
+        // So that vcruntime.lib and ucrt.lib are included when the entry point
+        // in msvcrt.lib is used. Using /NODEFAULTLIB would mean having to
+        // manually add those two libraries and potentially further dependencies
+        // they bring in.
+        //
+        // See also https://learn.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=msvc-170#lib
+        // for documention on including library dependencies in C/C++ code.
         no_default_libraries: false,
         has_thread_local: true,
 
