Disallow setting built-in cfgs via set the command-line

Author: Urgau

compiler/rustc_lint/messages.ftl

@@ -741,6 +741,10 @@ lint_undropped_manually_drops = calls to `std::mem::drop` with `std::mem::Manual
     .label = argument has type `{$arg_ty}`
     .suggestion = use `std::mem::ManuallyDrop::into_inner` to get the inner value
 
+lint_unexpected_builtin_cfg = unexpected `--cfg {$cfg}` flag
+    .controlled_by = config `{$cfg_name}` is only supposed to be controlled by `{$controlled_by}`
+    .incoherent = manually setting a built-in cfg does create incoherent behaviors
+
 lint_unexpected_cfg_add_build_rs_println = or consider adding `{$build_rs_println}` to the top of the `build.rs`
 lint_unexpected_cfg_add_cargo_feature = consider using a Cargo feature instead
 lint_unexpected_cfg_add_cargo_toml_lint_cfg = or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:{$cargo_toml_lint_cfg}

compiler/rustc_lint/src/context/diagnostics.rs

@@ -424,5 +424,8 @@ pub(super) fn decorate_lint(sess: &Session, diagnostic: BuiltinLintDiag, diag: &
             lints::InnerAttributeUnstable::CustomInnerAttribute
         }
         .decorate_lint(diag),
+        BuiltinLintDiag::UnexpectedBuiltinCfg { cfg, cfg_name, controlled_by } => {
+            lints::UnexpectedBuiltinCfg { cfg, cfg_name, controlled_by }.decorate_lint(diag)
+        }
     }
 }

compiler/rustc_lint/src/lints.rs

@@ -2319,6 +2319,16 @@ pub mod unexpected_cfg_value {
     }
 }
 
+#[derive(LintDiagnostic)]
+#[diag(lint_unexpected_builtin_cfg)]
+#[note(lint_controlled_by)]
+#[note(lint_incoherent)]
+pub struct UnexpectedBuiltinCfg {
+    pub(crate) cfg: String,
+    pub(crate) cfg_name: Symbol,
+    pub(crate) controlled_by: &'static str,
+}
+
 #[derive(LintDiagnostic)]
 #[diag(lint_macro_use_deprecated)]
 #[help]

compiler/rustc_lint_defs/src/builtin.rs

@@ -105,6 +105,7 @@ declare_lint_pass! {
         UNCONDITIONAL_RECURSION,
         UNCOVERED_PARAM_IN_PROJECTION,
         UNDEFINED_NAKED_FUNCTION_ABI,
+        UNEXPECTED_BUILTIN_CFGS,
         UNEXPECTED_CFGS,
         UNFULFILLED_LINT_EXPECTATIONS,
         UNINHABITED_STATIC,
@@ -3268,6 +3269,39 @@ declare_lint! {
     "detects unexpected names and values in `#[cfg]` conditions",
 }
 
+declare_lint! {
+    /// The `unexpected_builtin_cfgs` lint detects builtin cfgs set via the CLI, `--cfg`.
+    ///
+    /// ### Example
+    ///
+    /// ```text
+    /// rustc --cfg unix
+    /// ```
+    ///
+    /// ```rust,ignore (needs command line option)
+    /// fn main() {}
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// error: unexpected `--cfg unix` flag
+    ///   |
+    ///   = note: config `unix` is only supposed to be controlled by `--target`
+    ///   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+    ///   = note: `#[deny(unexpected_builtin_cfgs)]` on by default
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// Setting builtin cfgs can and does produce incoherent behavior, it's better to the use
+    /// the appropriate `rustc` flag that controls the config. For example setting the `windows`
+    /// cfg but on Linux based target.
+    pub UNEXPECTED_BUILTIN_CFGS,
+    Deny,
+    "detects builtin cfgs set via the `--cfg`"
+}
+
 declare_lint! {
     /// The `repr_transparent_external_private_fields` lint
     /// detects types marked `#[repr(transparent)]` that (transitively)

compiler/rustc_lint_defs/src/lib.rs

@@ -742,6 +742,11 @@ pub enum BuiltinLintDiag {
     InnerAttributeUnstable {
         is_macro: bool,
     },
+    UnexpectedBuiltinCfg {
+        cfg: String,
+        cfg_name: Symbol,
+        controlled_by: &'static str,
+    },
 }
 
 /// Lints that are buffered up early on in the `Session` before the

compiler/rustc_session/src/config.rs

@@ -1292,7 +1292,10 @@ pub(crate) const fn default_lib_output() -> CrateType {
 }
 
 pub fn build_configuration(sess: &Session, mut user_cfg: Cfg) -> Cfg {
-    // Combine the configuration requested by the session (command line) with
+    // First disallow some configuration given on the command line
+    cfg::disallow_cfgs(sess, &user_cfg);
+
+    // Then combine the configuration requested by the session (command line) with
     // some default and generated configuration items.
     user_cfg.extend(cfg::default_configuration(sess));
     user_cfg

compiler/rustc_session/src/config/cfg.rs

@@ -17,9 +17,13 @@
 //!  - Add the activation logic in [`default_configuration`]
 //!  - Add the cfg to [`CheckCfg::fill_well_known`] (and related files),
 //!    so that the compiler can know the cfg is expected
+//!  - Add the cfg in [`disallow_cfgs`] to disallow users from setting it via `--cfg`
 //!  - Add the feature gating in `compiler/rustc_feature/src/builtin_attrs.rs`
 
+use rustc_ast::ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
+use rustc_lint_defs::builtin::UNEXPECTED_BUILTIN_CFGS;
+use rustc_lint_defs::BuiltinLintDiag;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_target::abi::Align;
 use rustc_target::spec::{PanicStrategy, RelocModel, SanitizerSet};
@@ -83,6 +87,67 @@ impl<'a, T: Eq + Hash + Copy + 'a> Extend<&'a T> for ExpectedValues<T> {
     }
 }
 
+/// Disallow builtin cfgs from the CLI.
+pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
+    let disallow = |cfg: &(Symbol, Option<Symbol>), controlled_by| {
+        let cfg_name = cfg.0;
+        let cfg = if let Some(value) = cfg.1 {
+            format!(r#"{}="{}""#, cfg_name, value)
+        } else {
+            format!("{}", cfg_name)
+        };
+        sess.psess.opt_span_buffer_lint(
+            UNEXPECTED_BUILTIN_CFGS,
+            None,
+            ast::CRATE_NODE_ID,
+            BuiltinLintDiag::UnexpectedBuiltinCfg { cfg, cfg_name, controlled_by },
+        )
+    };
+
+    // We want to restrict setting builtin cfgs that will produce incoherent behavior
+    // between the cfg and the rustc cli flag that sets it.
+    //
+    // The tests are in tests/ui/cfg/disallowed-cli-cfgs.rs.
+
+    // By-default all builtin cfgs are disallowed, only those are allowed:
+    //  - test: as it makes sense to the have the `test` cfg active without the builtin
+    //          test harness. See Cargo `harness = false` config.
+    //
+    // Cargo `--cfg test`: https://github.com/rust-lang/cargo/blob/bc89bffa5987d4af8f71011c7557119b39e44a65/src/cargo/core/compiler/mod.rs#L1124
+
+    for cfg in user_cfgs {
+        match cfg {
+            (sym::overflow_checks, None) => disallow(cfg, "-C overflow-checks"),
+            (sym::debug_assertions, None) => disallow(cfg, "-C debug-assertions"),
+            (sym::ub_checks, None) => disallow(cfg, "-Z ub-checks"),
+            (sym::sanitize, None | Some(_)) => disallow(cfg, "-Z sanitizer"),
+            (
+                sym::sanitizer_cfi_generalize_pointers | sym::sanitizer_cfi_normalize_integers,
+                None | Some(_),
+            ) => disallow(cfg, "-Z sanitizer=cfi"),
+            (sym::proc_macro, None) => disallow(cfg, "--crate-type proc-macro"),
+            (sym::panic, Some(sym::abort | sym::unwind)) => disallow(cfg, "-C panic"),
+            (sym::target_feature, Some(_)) => disallow(cfg, "-C target-feature"),
+            (sym::unix, None)
+            | (sym::windows, None)
+            | (sym::relocation_model, Some(_))
+            | (sym::target_abi, None | Some(_))
+            | (sym::target_arch, Some(_))
+            | (sym::target_endian, Some(_))
+            | (sym::target_env, None | Some(_))
+            | (sym::target_family, Some(_))
+            | (sym::target_os, Some(_))
+            | (sym::target_pointer_width, Some(_))
+            | (sym::target_vendor, None | Some(_))
+            | (sym::target_has_atomic, Some(_))
+            | (sym::target_has_atomic_equal_alignment, Some(_))
+            | (sym::target_has_atomic_load_store, Some(_))
+            | (sym::target_thread_local, None) => disallow(cfg, "--target"),
+            _ => {}
+        }
+    }
+}
+
 /// Generate the default configs for a given session
 pub(crate) fn default_configuration(sess: &Session) -> Cfg {
     let mut ret = Cfg::default();

tests/codegen/aarch64-struct-align-128.rs

@@ -1,12 +1,12 @@
 // Test that structs aligned to 128 bits are passed with the correct ABI on aarch64.
 
-//@ revisions:linux darwin windows
+//@ revisions: linux darwin win
 //@[linux] compile-flags: --target aarch64-unknown-linux-gnu
 //@[darwin] compile-flags: --target aarch64-apple-darwin
-//@[windows] compile-flags: --target aarch64-pc-windows-msvc
+//@[win] compile-flags: --target aarch64-pc-windows-msvc
 //@[linux] needs-llvm-components: aarch64
 //@[darwin] needs-llvm-components: aarch64
-//@[windows] needs-llvm-components: aarch64
+//@[win] needs-llvm-components: aarch64
 
 #![feature(no_core, lang_items)]
 #![crate_type = "lib"]
@@ -41,7 +41,7 @@ pub struct Wrapped8 {
 extern "C" {
     // linux:   declare void @test_8([2 x i64], [2 x i64], [2 x i64])
     // darwin:  declare void @test_8([2 x i64], [2 x i64], [2 x i64])
-    // windows: declare void @test_8([2 x i64], [2 x i64], [2 x i64])
+    // win: declare void @test_8([2 x i64], [2 x i64], [2 x i64])
     fn test_8(a: Align8, b: Transparent8, c: Wrapped8);
 }
 
@@ -71,7 +71,7 @@ pub struct Wrapped16 {
 extern "C" {
     // linux:   declare void @test_16([2 x i64], [2 x i64], i128)
     // darwin:  declare void @test_16(i128, i128, i128)
-    // windows: declare void @test_16(i128, i128, i128)
+    // win: declare void @test_16(i128, i128, i128)
     fn test_16(a: Align16, b: Transparent16, c: Wrapped16);
 }
 
@@ -96,7 +96,7 @@ pub struct WrappedI128 {
 extern "C" {
     // linux:   declare void @test_i128(i128, i128, i128)
     // darwin:  declare void @test_i128(i128, i128, i128)
-    // windows: declare void @test_i128(i128, i128, i128)
+    // win: declare void @test_i128(i128, i128, i128)
     fn test_i128(a: I128, b: TransparentI128, c: WrappedI128);
 }
 
@@ -123,7 +123,7 @@ pub struct WrappedPacked {
 extern "C" {
     // linux:   declare void @test_packed([2 x i64], [2 x i64], [2 x i64])
     // darwin:  declare void @test_packed([2 x i64], [2 x i64], [2 x i64])
-    // windows: declare void @test_packed([2 x i64], [2 x i64], [2 x i64])
+    // win: declare void @test_packed([2 x i64], [2 x i64], [2 x i64])
     fn test_packed(a: Packed, b: TransparentPacked, c: WrappedPacked);
 }
 

tests/codegen/default-requires-uwtable.rs

@@ -1,9 +1,9 @@
-//@ revisions: WINDOWS ANDROID
+//@ revisions: WINDOWS_ ANDROID_
 //@ compile-flags: -C panic=abort -Copt-level=0
-//@ [WINDOWS] compile-flags: --target=x86_64-pc-windows-msvc
-//@ [WINDOWS] needs-llvm-components: x86
-//@ [ANDROID] compile-flags: --target=armv7-linux-androideabi
-//@ [ANDROID] needs-llvm-components: arm
+//@ [WINDOWS_] compile-flags: --target=x86_64-pc-windows-msvc
+//@ [WINDOWS_] needs-llvm-components: x86
+//@ [ANDROID_] compile-flags: --target=armv7-linux-androideabi
+//@ [ANDROID_] needs-llvm-components: arm
 
 #![feature(no_core, lang_items)]
 #![crate_type = "lib"]

tests/codegen/repr/transparent-sysv64.rs

@@ -1,12 +1,12 @@
-//@ revisions: linux apple windows
+//@ revisions: linux apple win
 //@ compile-flags: -O -C no-prepopulate-passes
 
 //@[linux] compile-flags: --target x86_64-unknown-linux-gnu
 //@[linux] needs-llvm-components: x86
 //@[apple] compile-flags: --target x86_64-apple-darwin
 //@[apple] needs-llvm-components: x86
-//@[windows] compile-flags: --target x86_64-pc-windows-msvc
-//@[windows] needs-llvm-components: x86
+//@[win] compile-flags: --target x86_64-pc-windows-msvc
+//@[win] needs-llvm-components: x86
 
 #![feature(no_core, lang_items)]
 #![crate_type = "lib"]