Clean up uses of the unstable dwarf_version option

- Consolidate calculation of the effective value.
- Check the target `DebuginfoKind` instead of using `is_like_msvc`.

Author: wesleywiser

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -919,8 +919,7 @@ pub(crate) fn build_compile_unit_di_node<'ll, 'tcx>(
         .unwrap_or_default();
     let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
 
-    let dwarf_version =
-        tcx.sess.opts.unstable_opts.dwarf_version.unwrap_or(tcx.sess.target.default_dwarf_version);
+    let dwarf_version = tcx.sess.dwarf_version();
     let is_dwarf_kind =
         matches!(tcx.sess.target.debuginfo_kind, DebuginfoKind::Dwarf | DebuginfoKind::DwarfDsym);
     // Don't emit `.debug_pubnames` and `.debug_pubtypes` on DWARFv4 or lower.

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -22,6 +22,7 @@ use rustc_session::config::{self, DebugInfo};
 use rustc_span::{
     BytePos, Pos, SourceFile, SourceFileAndLine, SourceFileHash, Span, StableSourceFileId, Symbol,
 };
+use rustc_target::spec::DebuginfoKind;
 use smallvec::SmallVec;
 use tracing::debug;
 
@@ -93,29 +94,31 @@ impl<'ll, 'tcx> CodegenUnitDebugContext<'ll, 'tcx> {
 
     pub(crate) fn finalize(&self, sess: &Session) {
         unsafe { llvm::LLVMRustDIBuilderFinalize(self.builder) };
-        if !sess.target.is_like_msvc {
-            // Debuginfo generation in LLVM by default uses a higher
-            // version of dwarf than macOS currently understands. We can
-            // instruct LLVM to emit an older version of dwarf, however,
-            // for macOS to understand. For more info see #11352
-            // This can be overridden using --llvm-opts -dwarf-version,N.
-            // Android has the same issue (#22398)
-            let dwarf_version =
-                sess.opts.unstable_opts.dwarf_version.unwrap_or(sess.target.default_dwarf_version);
-            llvm::add_module_flag_u32(
-                self.llmod,
-                llvm::ModuleFlagMergeBehavior::Warning,
-                "Dwarf Version",
-                dwarf_version,
-            );
-        } else {
-            // Indicate that we want CodeView debug information on MSVC
-            llvm::add_module_flag_u32(
-                self.llmod,
-                llvm::ModuleFlagMergeBehavior::Warning,
-                "CodeView",
-                1,
-            );
+
+        match sess.target.debuginfo_kind {
+            DebuginfoKind::Dwarf | DebuginfoKind::DwarfDsym => {
+                // Debuginfo generation in LLVM by default uses a higher
+                // version of dwarf than macOS currently understands. We can
+                // instruct LLVM to emit an older version of dwarf, however,
+                // for macOS to understand. For more info see #11352
+                // This can be overridden using --llvm-opts -dwarf-version,N.
+                // Android has the same issue (#22398)
+                llvm::add_module_flag_u32(
+                    self.llmod,
+                    llvm::ModuleFlagMergeBehavior::Warning,
+                    "Dwarf Version",
+                    sess.dwarf_version(),
+                );
+            }
+            DebuginfoKind::Pdb => {
+                // Indicate that we want CodeView debug information
+                llvm::add_module_flag_u32(
+                    self.llmod,
+                    llvm::ModuleFlagMergeBehavior::Warning,
+                    "CodeView",
+                    1,
+                );
+            }
         }
 
         // Prevent bitcode readers from deleting the debug info.

compiler/rustc_session/src/options.rs

@@ -1803,6 +1803,7 @@ options! {
         "output statistics about monomorphization collection"),
     dump_mono_stats_format: DumpMonoStatsFormat = (DumpMonoStatsFormat::Markdown, parse_dump_mono_stats, [UNTRACKED],
         "the format to use for -Z dump-mono-stats (`markdown` (default) or `json`)"),
+    #[rustc_lint_opt_deny_field_access("use `Session::dwarf_version` instead of this field")]
     dwarf_version: Option<u32> = (None, parse_opt_number, [TRACKED],
         "version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
     dylib_lto: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_session/src/session.rs

@@ -732,6 +732,11 @@ impl Session {
         self.opts.cg.split_debuginfo.unwrap_or(self.target.split_debuginfo)
     }
 
+    /// Returns the DWARF version passed on the CLI or the default for the target.
+    pub fn dwarf_version(&self) -> u32 {
+        self.opts.unstable_opts.dwarf_version.unwrap_or(self.target.default_dwarf_version)
+    }
+
     pub fn stack_protector(&self) -> StackProtector {
         if self.target.options.supports_stack_protector {
             self.opts.unstable_opts.stack_protector
@@ -1263,8 +1268,7 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
     }
 
     if sess.opts.unstable_opts.embed_source {
-        let dwarf_version =
-            sess.opts.unstable_opts.dwarf_version.unwrap_or(sess.target.default_dwarf_version);
+        let dwarf_version = sess.dwarf_version();
 
         if dwarf_version < 5 {
             sess.dcx().emit_warn(errors::EmbedSourceInsufficientDwarfVersion { dwarf_version });