Preserve, clarify, and extend debug information

`-Cdebuginfo=1` was never line tables only and
can't be due to backwards compatibility issues.
This was clarified and an option for line tables only
was added. Additionally an option for line info
directives only was added, which is well needed for
some targets. The debug info options should now
behave the same as clang's debug info options.

Author: jdtatz

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1019,24 +1019,7 @@ pub fn compile_unit_metadata(
     }
     .unwrap_or_default();
     let split_name = split_name.to_str().unwrap();
-
-    // FIXME(#60020):
-    //
-    //    This should actually be
-    //
-    //        let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
-    //
-    //    That is, we should set LLVM's emission kind to `LineTablesOnly` if
-    //    we are compiling with "limited" debuginfo. However, some of the
-    //    existing tools relied on slightly more debuginfo being generated than
-    //    would be the case with `LineTablesOnly`, and we did not want to break
-    //    these tools in a "drive-by fix", without a good idea or plan about
-    //    what limited debuginfo should exactly look like. So for now we keep
-    //    the emission kind as `FullDebug`.
-    //
-    //    See https://github.com/rust-lang/rust/issues/60020 for details.
-    let kind = DebugEmissionKind::FullDebug;
-    assert!(tcx.sess.opts.debuginfo != DebugInfo::None);
+    let kind = DebugEmissionKind::from_generic(tcx.sess.opts.debuginfo);
 
     unsafe {
         let compile_unit_file = llvm::LLVMRustDIBuilderCreateFile(

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -372,7 +372,7 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             cx: &CodegenCx<'ll, 'tcx>,
             fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
         ) -> &'ll DIArray {
-            if cx.sess().opts.debuginfo == DebugInfo::Limited {
+            if cx.sess().opts.debuginfo != DebugInfo::Full {
                 return create_DIArray(DIB(cx), &[]);
             }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -872,15 +872,17 @@ pub mod debuginfo {
         NoDebug,
         FullDebug,
         LineTablesOnly,
+        DebugDirectivesOnly,
     }
 
     impl DebugEmissionKind {
         pub fn from_generic(kind: rustc_session::config::DebugInfo) -> Self {
             use rustc_session::config::DebugInfo;
             match kind {
                 DebugInfo::None => DebugEmissionKind::NoDebug,
-                DebugInfo::Limited => DebugEmissionKind::LineTablesOnly,
-                DebugInfo::Full => DebugEmissionKind::FullDebug,
+                DebugInfo::LineDirectivesOnly => DebugEmissionKind::DebugDirectivesOnly,
+                DebugInfo::LineTablesOnly => DebugEmissionKind::LineTablesOnly,
+                DebugInfo::Limited | DebugInfo::Full => DebugEmissionKind::FullDebug,
             }
         }
     }

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1114,8 +1114,11 @@ impl<'a> Linker for EmLinker<'a> {
 
     fn debuginfo(&mut self, _strip: Strip) {
         // Preserve names or generate source maps depending on debug info
+        // For more information see https://emscripten.org/docs/tools_reference/emcc.html#emcc-g
         self.cmd.arg(match self.sess.opts.debuginfo {
             DebugInfo::None => "-g0",
+            DebugInfo::LineDirectivesOnly => "-g3",
+            DebugInfo::LineTablesOnly => "-g3",
             DebugInfo::Limited => "-g3",
             DebugInfo::Full => "-g4",
         });

compiler/rustc_interface/src/tests.rs

@@ -8,7 +8,7 @@ use rustc_session::config::{build_configuration, build_session_options, to_crate
 use rustc_session::config::{rustc_optgroups, ErrorOutputType, ExternLocation, Options, Passes};
 use rustc_session::config::{CFGuard, ExternEntry, LinkerPluginLto, LtoCli, SwitchWithOptPath};
 use rustc_session::config::{
-    Externs, OutputType, OutputTypes, SymbolManglingVersion, WasiExecModel,
+    DebugInfo, Externs, OutputType, OutputTypes, SymbolManglingVersion, WasiExecModel,
 };
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
@@ -564,7 +564,7 @@ fn test_codegen_options_tracking_hash() {
     tracked!(code_model, Some(CodeModel::Large));
     tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(debug_assertions, Some(true));
-    tracked!(debuginfo, 0xdeadbeef);
+    tracked!(debuginfo, DebugInfo::Limited);
     tracked!(embed_bitcode, false);
     tracked!(force_frame_pointers, Some(false));
     tracked!(force_unwind_tables, Some(true));

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -641,6 +641,7 @@ enum class LLVMRustDebugEmissionKind {
   NoDebug,
   FullDebug,
   LineTablesOnly,
+  DebugDirectivesOnly,
 };
 
 static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind) {
@@ -651,6 +652,8 @@ static DICompileUnit::DebugEmissionKind fromRust(LLVMRustDebugEmissionKind Kind)
     return DICompileUnit::DebugEmissionKind::FullDebug;
   case LLVMRustDebugEmissionKind::LineTablesOnly:
     return DICompileUnit::DebugEmissionKind::LineTablesOnly;
+  case LLVMRustDebugEmissionKind::DebugDirectivesOnly:
+    return DICompileUnit::DebugEmissionKind::DebugDirectivesOnly;
   default:
     report_fatal_error("bad DebugEmissionKind.");
   }

compiler/rustc_session/src/config.rs

@@ -201,6 +201,8 @@ impl_stable_hash_via_hash!(SymbolManglingVersion);
 #[derive(Clone, Copy, Debug, PartialEq, Hash)]
 pub enum DebugInfo {
     None,
+    LineDirectivesOnly,
+    LineTablesOnly,
     Limited,
     Full,
 }
@@ -1561,11 +1563,7 @@ fn parse_opt_level(
     }
 }
 
-fn select_debuginfo(
-    matches: &getopts::Matches,
-    cg: &CodegenOptions,
-    error_format: ErrorOutputType,
-) -> DebugInfo {
+fn select_debuginfo(matches: &getopts::Matches, cg: &CodegenOptions) -> DebugInfo {
     let max_g = matches.opt_positions("g").into_iter().max();
     let max_c = matches
         .opt_strs_pos("C")
@@ -1575,25 +1573,7 @@ fn select_debuginfo(
             if let Some("debuginfo") = s.splitn(2, '=').next() { Some(i) } else { None }
         })
         .max();
-    if max_g > max_c {
-        DebugInfo::Full
-    } else {
-        match cg.debuginfo {
-            0 => DebugInfo::None,
-            1 => DebugInfo::Limited,
-            2 => DebugInfo::Full,
-            arg => {
-                early_error(
-                    error_format,
-                    &format!(
-                        "debug info level needs to be between \
-                         0-2 (instead was `{}`)",
-                        arg
-                    ),
-                );
-            }
-        }
-    }
+    if max_g > max_c { DebugInfo::Full } else { cg.debuginfo }
 }
 
 fn parse_native_lib_kind(
@@ -2055,7 +2035,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
     // to use them interchangeably. See the note above (regarding `-O` and `-C opt-level`)
     // for more details.
     let debug_assertions = cg.debug_assertions.unwrap_or(opt_level == OptLevel::No);
-    let debuginfo = select_debuginfo(matches, &cg, error_format);
+    let debuginfo = select_debuginfo(matches, &cg);
 
     let mut search_paths = vec![];
     for s in &matches.opt_strs("L") {

compiler/rustc_session/src/options.rs

@@ -355,6 +355,7 @@ mod desc {
     pub const parse_sanitizer_memory_track_origins: &str = "0, 1, or 2";
     pub const parse_cfguard: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `checks`, or `nochecks`";
+    pub const parse_debuginfo: &str = "either an integer (0, 1, 2), `none`, `line-directives-only`, `line-tables-only`, `limited`, or `full`";
     pub const parse_strip: &str = "either `none`, `debuginfo`, or `symbols`";
     pub const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavor::one_of();
     pub const parse_optimization_fuel: &str = "crate=integer";
@@ -509,17 +510,6 @@ mod parse {
         }
     }
 
-    /// Use this for any numeric option that has a static default.
-    crate fn parse_number<T: Copy + FromStr>(slot: &mut T, v: Option<&str>) -> bool {
-        match v.and_then(|s| s.parse().ok()) {
-            Some(i) => {
-                *slot = i;
-                true
-            }
-            None => false,
-        }
-    }
-
     /// Use this for any numeric option that lacks a static default.
     crate fn parse_opt_number<T: Copy + FromStr>(slot: &mut Option<T>, v: Option<&str>) -> bool {
         match v {
@@ -633,6 +623,18 @@ mod parse {
         true
     }
 
+    crate fn parse_debuginfo(slot: &mut DebugInfo, v: Option<&str>) -> bool {
+        match v {
+            Some("0") | Some("none") => *slot = DebugInfo::None,
+            Some("line-directives-only") => *slot = DebugInfo::LineDirectivesOnly,
+            Some("line-tables-only") => *slot = DebugInfo::LineTablesOnly,
+            Some("1") | Some("limited") => *slot = DebugInfo::Limited,
+            Some("2") | Some("full") => *slot = DebugInfo::Full,
+            _ => return false,
+        }
+        true
+    }
+
     crate fn parse_linker_flavor(slot: &mut Option<LinkerFlavor>, v: Option<&str>) -> bool {
         match v.and_then(LinkerFlavor::from_str) {
             Some(lf) => *slot = Some(lf),
@@ -905,9 +907,9 @@ options! {
         "use Windows Control Flow Guard (default: no)"),
     debug_assertions: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the `cfg(debug_assertions)` directive"),
-    debuginfo: usize = (0, parse_number, [TRACKED],
-        "debug info emission level (0 = no debug info, 1 = line tables only, \
-        2 = full debug info with variable and type information; default: 0)"),
+    debuginfo: DebugInfo = (DebugInfo::None, parse_debuginfo, [TRACKED],
+        "debug info emission level (0-2, none, line-directives-only, \
+        line-tables-only, limited, or full; default: 0)"),
     default_linker_libraries: bool = (false, parse_bool, [UNTRACKED],
         "allow the linker to link its default libraries (default: no)"),
     embed_bitcode: bool = (true, parse_bool, [TRACKED],

src/doc/rustc/src/codegen-options/index.md

@@ -71,9 +71,11 @@ If not specified, debug assertions are automatically enabled only if the
 This flag controls the generation of debug information. It takes one of the
 following values:
 
-* `0`: no debug info at all (the default).
-* `1`: line tables only.
-* `2`: full debug info.
+* `0` or `none`: no debug info at all (the default).
+* `line-directives-only`: line info directives only.
+* `line-tables-only`: line tables only.
+* `1` or `limited`: debug info without type information.
+* `2` or `full`: full debug info.
 
 Note: The [`-g` flag][option-g-debug] is an alias for `-C debuginfo=2`.
 

src/test/codegen/debug-limited.rs

@@ -0,0 +1,28 @@
+// Verify that the limited debuginfo option emits llvm's FullDebugInfo, but no type info.
+//
+// ignore-windows
+// compile-flags: -C debuginfo=limited
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut* creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: FullDebug
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType

src/test/codegen/debug-line-directives-only.rs

@@ -0,0 +1,28 @@
+// Verify that the only debuginfo generated are the line directives.
+//
+// ignore-windows
+// compile-flags: -C debuginfo=line-directives-only
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut* creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: DebugDirectivesOnly
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType

src/test/codegen/debug-line-tables-only.rs

@@ -0,0 +1,28 @@
+// Verify that the only debuginfo generated are the line tables.
+//
+// ignore-windows
+// compile-flags: -C debuginfo=line-tables-only
+
+#[repr(C)]
+struct StructType {
+    a: i64,
+    b: i32
+}
+
+extern "C" {
+    fn creator() -> *mut StructType;
+    fn save(p: *const StructType);
+}
+
+fn main() {
+    unsafe {
+        let value: &mut StructType = &mut* creator();
+        value.a = 7;
+        save(value as *const StructType)
+    }
+}
+
+// CHECK: !DICompileUnit
+// CHECK: emissionKind: LineTablesOnly
+// CHECK: !DILocation
+// CHECK-NOT: !DIBasicType