rust-lang · azhogin · Mar 9, 2025 · wesleywiser · Mar 13, 2025 · Noratrieb
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -39,6 +39,7 @@ const GATED_CFGS: &[GatedCfg] = &[
     // this is consistent with naming of the compiler flag it's for
     (sym::fmt_debug, sym::fmt_debug, Features::fmt_debug),
     (sym::emscripten_wasm_eh, sym::cfg_emscripten_wasm_eh, Features::cfg_emscripten_wasm_eh),
+    (sym::c_char_type, sym::c_char_type, Features::c_char_type),
 ];
 
 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.

diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
@@ -390,6 +390,8 @@ declare_features! (
     (unstable, async_for_loop, "1.77.0", Some(118898)),
     /// Allows `async` trait bound modifier.
     (unstable, async_trait_bounds, "1.85.0", Some(62290)),
+    // Allows customized c_char type (u8/i8)
+    (unstable, c_char_type, "1.86.0", Some(138446)),
     /// Allows using C-variadics.
     (unstable, c_variadic, "1.34.0", Some(44930)),
     /// Allows the use of `#[cfg(<true/false>)]`.

diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
@@ -9,7 +9,7 @@ use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_errors::emitter::HumanReadableErrorType;
 use rustc_errors::{ColorConfig, registry};
 use rustc_session::config::{
-    AutoDiff, BranchProtection, CFGuard, Cfg, CollapseMacroDebuginfo, CoverageLevel,
+    AutoDiff, BranchProtection, CCharType, CFGuard, Cfg, CollapseMacroDebuginfo, CoverageLevel,
     CoverageOptions, DebugInfo, DumpMonoStatsFormat, ErrorOutputType, ExternEntry, ExternLocation,
     Externs, FmtDebug, FunctionReturn, InliningThreshold, Input, InstrumentCoverage,
     InstrumentXRay, LinkSelfContained, LinkerPluginLto, LocationDetail, LtoCli, MirIncludeSpans,
@@ -769,6 +769,7 @@ fn test_unstable_options_tracking_hash() {
             pac_ret: Some(PacRet { leaf: true, pc: true, key: PAuthKey::B })
         })
     );
+    tracked!(c_char_type, CCharType::Unsigned);
     tracked!(codegen_backend, Some("abc".to_string()));
     tracked!(
         coverage_options,

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
@@ -23,7 +23,7 @@ use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::edition::{DEFAULT_EDITION, EDITION_NAME_LIST, Edition, LATEST_STABLE_EDITION};
 use rustc_span::source_map::FilePathMapping;
 use rustc_span::{
-    FileName, FileNameDisplayPreference, RealFileName, SourceFileHashAlgorithm, Symbol, sym,
+    FileName, FileNameDisplayPreference, RealFileName, SourceFileHashAlgorithm, Symbol, kw, sym,
 };
 use rustc_target::spec::{
     FramePointer, LinkSelfContainedComponents, LinkerFeatures, SplitDebuginfo, Target, TargetTuple,
@@ -2931,13 +2931,13 @@ pub(crate) mod dep_tracking {
     };
 
     use super::{
-        AutoDiff, BranchProtection, CFGuard, CFProtection, CollapseMacroDebuginfo, CoverageOptions,
-        CrateType, DebugInfo, DebugInfoCompression, ErrorOutputType, FmtDebug, FunctionReturn,
-        InliningThreshold, InstrumentCoverage, InstrumentXRay, LinkerPluginLto, LocationDetail,
-        LtoCli, MirStripDebugInfo, NextSolverConfig, OomStrategy, OptLevel, OutFileName,
-        OutputType, OutputTypes, PatchableFunctionEntry, Polonius, RemapPathScopeComponents,
-        ResolveDocLinks, SourceFileHashAlgorithm, SplitDwarfKind, SwitchWithOptPath,
-        SymbolManglingVersion, WasiExecModel,
+        AutoDiff, BranchProtection, CCharType, CFGuard, CFProtection, CollapseMacroDebuginfo,
+        CoverageOptions, CrateType, DebugInfo, DebugInfoCompression, ErrorOutputType, FmtDebug,
+        FunctionReturn, InliningThreshold, InstrumentCoverage, InstrumentXRay, LinkerPluginLto,
+        LocationDetail, LtoCli, MirStripDebugInfo, NextSolverConfig, OomStrategy, OptLevel,
+        OutFileName, OutputType, OutputTypes, PatchableFunctionEntry, Polonius,
+        RemapPathScopeComponents, ResolveDocLinks, SourceFileHashAlgorithm, SplitDwarfKind,
+        SwitchWithOptPath, SymbolManglingVersion, WasiExecModel,
     };
     use crate::lint;
     use crate::utils::NativeLib;
@@ -3040,6 +3040,7 @@ pub(crate) mod dep_tracking {
         FunctionReturn,
         WasmCAbi,
         Align,
+        CCharType,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)
@@ -3314,3 +3315,31 @@ impl MirIncludeSpans {
         self == MirIncludeSpans::On
     }
 }
+
+/// The different settings that the `-Zc-char-type` flag can have.
+#[derive(Clone, Copy, PartialEq, Hash, Debug, Default)]
+pub enum CCharType {
+    /// Use default signed/unsigned c_char according to target configuration
+    #[default]
+    Default,
+
+    /// Set c_char to signed i8
+    Signed,
+
+    /// Set c_char to unsigned u8
+    Unsigned,
+}
+
+impl CCharType {
+    pub const fn desc_symbol(&self) -> Symbol {
+        match *self {
+            Self::Default => kw::Default,
+            Self::Signed => sym::signed,
+            Self::Unsigned => sym::unsigned,
+        }
+    }
+
+    pub const fn all() -> [Symbol; 3] {
+        [Self::Unsigned.desc_symbol(), Self::Signed.desc_symbol(), Self::Default.desc_symbol()]
+    }
+}
diff --git a/compiler/rustc_session/src/config/cfg.rs b/compiler/rustc_session/src/config/cfg.rs
@@ -32,7 +32,7 @@ use rustc_span::{Symbol, sym};
 use rustc_target::spec::{PanicStrategy, RelocModel, SanitizerSet, Target};
 
 use crate::Session;
-use crate::config::{CrateType, FmtDebug};
+use crate::config::{CCharType, CrateType, FmtDebug};
 
 /// The parsed `--cfg` options that define the compilation environment of the
 /// crate, used to drive conditional compilation.
@@ -144,6 +144,7 @@ pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
             | (sym::target_has_atomic_load_store, Some(_))
             | (sym::target_thread_local, None) => disallow(cfg, "--target"),
             (sym::fmt_debug, None | Some(_)) => disallow(cfg, "-Z fmt-debug"),
+            (sym::c_char_type, None | Some(_)) => disallow(cfg, "-Z c-char-type"),
             (sym::emscripten_wasm_eh, None | Some(_)) => disallow(cfg, "-Z emscripten_wasm_eh"),
             _ => {}
         }
@@ -306,6 +307,10 @@ pub(crate) fn default_configuration(sess: &Session) -> Cfg {
         ins_none!(sym::contract_checks);
     }
 
+    if sess.is_nightly_build() {
+        ins_sym!(sym::c_char_type, sess.opts.unstable_opts.c_char_type.desc_symbol());
+    }
+
     ret
 }
 
@@ -470,5 +475,7 @@ impl CheckCfg {
 
         ins!(sym::unix, no_values);
         ins!(sym::windows, no_values);
+
+        ins!(sym::c_char_type, empty_values).extend(CCharType::all());
     }
 }
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
@@ -794,6 +794,7 @@ mod desc {
     pub(crate) const parse_mir_include_spans: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), or `nll` (default: `nll`)";
     pub(crate) const parse_align: &str = "a number that is a power of 2 between 1 and 2^29";
+    pub(crate) const parse_c_char_type: &str = "one of `default`, `unsigned`, `signed`";
 }
 
 pub mod parse {
@@ -954,6 +955,16 @@ pub mod parse {
         true
     }
 
+    pub(crate) fn parse_c_char_type(slot: &mut CCharType, v: Option<&str>) -> bool {
+        *slot = match v {
+            Some("unsigned") => CCharType::Unsigned,
+            Some("signed") => CCharType::Signed,
+            Some("default") => CCharType::Default,
+            _ => return false,
+        };
+        true
+    }
+
     pub(crate) fn parse_location_detail(ld: &mut LocationDetail, v: Option<&str>) -> bool {
         if let Some(v) = v {
             ld.line = false;
@@ -2099,6 +2110,8 @@ options! {
         "emit noalias metadata for box (default: yes)"),
     branch_protection: Option<BranchProtection> = (None, parse_branch_protection, [TRACKED],
         "set options for branch target identification and pointer authentication on AArch64"),
+    c_char_type: CCharType = (CCharType::default(), parse_c_char_type, [TRACKED TARGET_MODIFIER],
+        "Make c_char type unsigned [default|signed|unsigned]"),
     cf_protection: CFProtection = (CFProtection::None, parse_cfprotection, [TRACKED],
         "instrument control-flow architecture protection"),
     check_cfg_all_expected: bool = (false, parse_bool, [UNTRACKED],

diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -557,6 +557,7 @@ symbols! {
         btreeset_iter,
         builtin_syntax,
         c,
+        c_char_type,
         c_dash_variadic,
         c_str,
         c_str_literals,
@@ -1855,6 +1856,7 @@ symbols! {
         shr_assign,
         sig_dfl,
         sig_ign,
+        signed,
         simd,
         simd_add,
         simd_and,
@@ -2169,6 +2171,7 @@ symbols! {
         unsafe_fields,
         unsafe_no_drop_flag,
         unsafe_pin_internals,
+        unsigned,
         unsize,
         unsized_const_param_ty,
         unsized_const_params,

diff --git a/library/core/Cargo.toml b/library/core/Cargo.toml
@@ -25,6 +25,8 @@ optimize_for_size = []
 debug_refcell = []
 # Make `TypeId` store a reference to the name of the type, so that it can print that name.
 debug_typeid = []
+#Allow -Zc-char-type='unsigned|signed|default' for c_char override
+c_char_type = []
 
 [lints.rust.unexpected_cfgs]
 level = "warn"
@@ -38,4 +40,5 @@ check-cfg = [
     # and to stdarch `core_arch` crate which messes-up with Cargo list
     # of declared features, we therefor expect any feature cfg
     'cfg(feature, values(any()))',
+    'cfg(c_char_type, values(any()))'
 ]
diff --git a/library/core/src/ffi/primitives.rs b/library/core/src/ffi/primitives.rs
@@ -105,28 +105,59 @@ mod c_char_definition {
         //   architecture defaults). As we only have a target for userspace apps so there are no
         //   special cases for L4Re below.
         //   https://github.com/rust-lang/rust/pull/132975#issuecomment-2484645240
-        if #[cfg(all(
-            not(windows),
-            not(target_vendor = "apple"),
-            not(target_os = "vita"),
-            any(
-                target_arch = "aarch64",
-                target_arch = "arm",
-                target_arch = "csky",
-                target_arch = "hexagon",
-                target_arch = "msp430",
-                target_arch = "powerpc",
-                target_arch = "powerpc64",
-                target_arch = "riscv32",
-                target_arch = "riscv64",
-                target_arch = "s390x",
-                target_arch = "xtensa",
-            )
-        ))] {
-            pub(super) type c_char = u8;
+        if #[cfg(feature = "c_char_type")] {
+            cfg_if! {
+                if #[cfg(any(c_char_type = "unsigned", all(
+                    not(c_char_type = "signed"),
+                    not(windows),
+                    not(target_vendor = "apple"),
+                    not(target_os = "vita"),
+                    any(
+                        target_arch = "aarch64",
+                        target_arch = "arm",
+                        target_arch = "csky",
+                        target_arch = "hexagon",
+                        target_arch = "msp430",
+                        target_arch = "powerpc",
+                        target_arch = "powerpc64",
+                        target_arch = "riscv32",
+                        target_arch = "riscv64",
+                        target_arch = "s390x",
+                        target_arch = "xtensa",
+                    )
+                )))] {
+                    pub(super) type c_char = u8;
+                } else {
+                    // On every other target, c_char is signed.
+                    pub(super) type c_char = i8;
+                }
+            }
         } else {
-            // On every other target, c_char is signed.
-            pub(super) type c_char = i8;
+            cfg_if! {
+                if #[cfg(all(
+                    not(windows),
+                    not(target_vendor = "apple"),
+                    not(target_os = "vita"),
+                    any(
+                        target_arch = "aarch64",
+                        target_arch = "arm",
+                        target_arch = "csky",
+                        target_arch = "hexagon",
+                        target_arch = "msp430",
+                        target_arch = "powerpc",
+                        target_arch = "powerpc64",
+                        target_arch = "riscv32",
+                        target_arch = "riscv64",
+                        target_arch = "s390x",
+                        target_arch = "xtensa",
+                    )
+                ))] {
+                    pub(super) type c_char = u8;
+                } else {
+                    // On every other target, c_char is signed.
+                    pub(super) type c_char = i8;
+                }
+            }
         }
     }
 }

diff --git a/tests/ui/cfg/disallowed-cli-cfgs.c_char_type_.stderr b/tests/ui/cfg/disallowed-cli-cfgs.c_char_type_.stderr
@@ -0,0 +1,8 @@
+error: unexpected `--cfg c_char_type="unsigned"` flag
+   |
+   = note: config `c_char_type` is only supposed to be controlled by `-Z c-char-type`
+   = note: manually setting a built-in cfg can and does create incoherent behaviors
+   = note: `#[deny(explicit_builtin_cfgs_in_flags)]` on by default
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/cfg/disallowed-cli-cfgs.rs b/tests/ui/cfg/disallowed-cli-cfgs.rs
@@ -8,6 +8,7 @@
 //@ revisions: target_thread_local_ relocation_model_
 //@ revisions: fmt_debug_
 //@ revisions: emscripten_wasm_eh_
+//@ revisions: c_char_type_
 
 //@ [overflow_checks_]compile-flags: --cfg overflow_checks
 //@ [debug_assertions_]compile-flags: --cfg debug_assertions
@@ -35,5 +36,6 @@
 //@ [relocation_model_]compile-flags: --cfg relocation_model="a"
 //@ [fmt_debug_]compile-flags: --cfg fmt_debug="shallow"
 //@ [emscripten_wasm_eh_]compile-flags: --cfg emscripten_wasm_eh
+//@ [c_char_type_]compile-flags: --cfg c_char_type="unsigned"
 
 fn main() {}
diff --git a/tests/ui/check-cfg/cargo-build-script.stderr b/tests/ui/check-cfg/cargo-build-script.stderr
@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `has_foo`
 LL | #[cfg(has_foo)]
    |       ^^^^^^^
    |
-   = help: expected names are: `has_bar` and 31 more
+   = help: expected names are: `has_bar` and 32 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]

diff --git a/tests/ui/check-cfg/cargo-feature.none.stderr b/tests/ui/check-cfg/cargo-feature.none.stderr
@@ -25,7 +25,7 @@ warning: unexpected `cfg` condition name: `tokio_unstable`
 LL | #[cfg(tokio_unstable)]
    |       ^^^^^^^^^^^^^^
    |
-   = help: expected names are: `docsrs`, `feature`, and `test` and 31 more
+   = help: expected names are: `docsrs`, `feature`, and `test` and 32 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]

diff --git a/tests/ui/check-cfg/cargo-feature.some.stderr b/tests/ui/check-cfg/cargo-feature.some.stderr
@@ -25,7 +25,7 @@ warning: unexpected `cfg` condition name: `tokio_unstable`
 LL | #[cfg(tokio_unstable)]
    |       ^^^^^^^^^^^^^^
    |
-   = help: expected names are: `CONFIG_NVME`, `docsrs`, `feature`, and `test` and 31 more
+   = help: expected names are: `CONFIG_NVME`, `docsrs`, `feature`, and `test` and 32 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]

diff --git a/tests/ui/check-cfg/cfg-value-for-cfg-name-duplicate.stderr b/tests/ui/check-cfg/cfg-value-for-cfg-name-duplicate.stderr
@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `value`
 LL | #[cfg(value)]
    |       ^^^^^
    |
-   = help: expected names are: `bar`, `bee`, `cow`, and `foo` and 31 more
+   = help: expected names are: `bar`, `bee`, `cow`, and `foo` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(value)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

diff --git a/tests/ui/check-cfg/cfg-value-for-cfg-name-multiple.stderr b/tests/ui/check-cfg/cfg-value-for-cfg-name-multiple.stderr
@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `my_value`
 LL | #[cfg(my_value)]
    |       ^^^^^^^^
    |
-   = help: expected names are: `bar` and `foo` and 31 more
+   = help: expected names are: `bar` and `foo` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(my_value)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

diff --git a/tests/ui/check-cfg/exhaustive-names-values.feature.stderr b/tests/ui/check-cfg/exhaustive-names-values.feature.stderr
@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `feature` and 31 more
+   = help: expected names are: `feature` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

diff --git a/tests/ui/check-cfg/exhaustive-names-values.full.stderr b/tests/ui/check-cfg/exhaustive-names-values.full.stderr
@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `feature` and 31 more
+   = help: expected names are: `feature` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

diff --git a/tests/ui/check-cfg/mix.stderr b/tests/ui/check-cfg/mix.stderr
@@ -44,7 +44,7 @@ warning: unexpected `cfg` condition name: `uu`
 LL | #[cfg_attr(uu, unix)]
    |            ^^
    |
-   = help: expected names are: `feature` and 31 more
+   = help: expected names are: `feature` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(uu)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
 

diff --git a/tests/ui/check-cfg/raw-keywords.edition2015.stderr b/tests/ui/check-cfg/raw-keywords.edition2015.stderr
@@ -14,7 +14,7 @@ warning: unexpected `cfg` condition name: `r#false`
 LL | #[cfg(r#false)]
    |       ^^^^^^^
    |
-   = help: expected names are: `async`, `edition2015`, `edition2021`, and `r#true` and 31 more
+   = help: expected names are: `async`, `edition2015`, `edition2021`, and `r#true` and 32 more
    = help: to expect this configuration use `--check-cfg=cfg(r#false)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration