Disallow setting some built-in cfg via set the command-line

Author: Urgau

compiler/rustc_session/messages.ftl

@@ -14,6 +14,10 @@ session_crate_name_empty = crate name must not be empty
 
 session_crate_name_invalid = crate names cannot start with a `-`, but `{$s}` has a leading hyphen
 
+session_disallow_cli_cfg = unexpected `--cfg {$cfg}` flag
+    .controlled_by = config `{$cfg_name}` is only supposed to be controlled by `{$controlled_by}`
+    .issue = see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+
 session_expr_parentheses_needed = parentheses are required to parse this as an expression
 
 session_failed_to_create_profiler = failed to create profiler: {$err}

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

@@ -26,6 +26,7 @@ use rustc_target::spec::{PanicStrategy, RelocModel, SanitizerSet};
 use rustc_target::spec::{Target, TargetTriple, TARGETS};
 
 use crate::config::CrateType;
+use crate::errors::DisallowConfig;
 use crate::Session;
 
 use std::hash::Hash;
@@ -379,3 +380,54 @@ impl CheckCfg {
         ins!(sym::windows, no_values);
     }
 }
+
+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.dcx().emit_fatal(DisallowConfig { cfg, cfg_name, controlled_by })
+    };
+
+    // We want to restrict setting cfgs that will produce "incoherent" behavior between
+    // the cfg and the "real" flag that sets it, but not all cfgs produce incoherent
+    // behavior, we therefore exclude those cfgs:
+    //
+    //  - test
+    //  - clippy
+    //  - doc
+    //  - doctest
+    //  - miri
+    //  - rustfmt
+    //  - overflow_checks
+    //  - debug_assertions
+    //  - ub_checks
+
+    for cfg in user_cfgs {
+        match cfg {
+            (sym::proc_macro, None) => disallow(cfg, "--crate-type proc-macro"),
+            (sym::panic, Some(sym::abort)) => disallow(cfg, "-C panic"),
+            (sym::panic, Some(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"),
+            _ => {}
+        }
+    }
+}

compiler/rustc_session/src/errors.rs

@@ -472,3 +472,13 @@ pub(crate) struct FunctionReturnThunkExternRequiresNonLargeCodeModel;
 pub(crate) struct FailedToCreateProfiler {
     pub(crate) err: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(session_disallow_cli_cfg)]
+#[note(session_controlled_by)]
+#[note(session_issue)]
+pub(crate) struct DisallowConfig {
+    pub(crate) cfg: String,
+    pub(crate) cfg_name: Symbol,
+    pub(crate) controlled_by: &'static str,
+}

tests/ui/cfg/disallowed-cli-cfgs.debug_assertions.stderr

@@ -0,0 +1,5 @@
+error: unexpected `--cfg debug_assertions` flag
+   |
+   = note: config `debug_assertions` is only supposed to be controlled by `-C debug_assertions`
+   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+

tests/ui/cfg/disallowed-cli-cfgs.panic.stderr

@@ -0,0 +1,5 @@
+error: unexpected `--cfg panic="abort"` flag
+   |
+   = note: config `panic` is only supposed to be controlled by `-C panic`
+   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+

tests/ui/cfg/disallowed-cli-cfgs.proc_macro.stderr

@@ -0,0 +1,5 @@
+error: unexpected `--cfg proc_macro` flag
+   |
+   = note: config `proc_macro` is only supposed to be controlled by `--crate-type proc-macro`
+   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+

tests/ui/cfg/disallowed-cli-cfgs.relocation_model.stderr

@@ -0,0 +1,5 @@
+error: unexpected `--cfg relocation_model="a"` flag
+   |
+   = note: config `relocation_model` is only supposed to be controlled by `--target`
+   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+

tests/ui/cfg/disallowed-cli-cfgs.rs

@@ -0,0 +1,27 @@
+//@ check-fail
+//@ revisions: proc_macro panic target_feature unix windows target_abi
+//@ revisions: target_arch target_endian target_env target_family target_os target_pointer_width
+//@ revisions: target_vendor target_has_atomic target_has_atomic_equal_alignment
+//@ revisions: target_has_atomic_load_store target_thread_local relocation_model
+
+//@ [proc_macro]compile-flags: --cfg proc_macro
+//@ [panic]compile-flags: --cfg panic="abort"
+//@ [target_feature]compile-flags: --cfg target_feature="sse3"
+//@ [unix]compile-flags: --cfg unix
+//@ [windows]compile-flags: --cfg windows
+//@ [target_abi]compile-flags: --cfg target_abi="gnu"
+//@ [target_arch]compile-flags: --cfg target_arch="arm"
+//@ [target_endian]compile-flags: --cfg target_endian="little"
+//@ [target_env]compile-flags: --cfg target_env
+//@ [target_family]compile-flags: --cfg target_family="unix"
+//@ [target_os]compile-flags: --cfg target_os="linux"
+//@ [target_pointer_width]compile-flags: --cfg target_pointer_width="32"
+//@ [target_vendor]compile-flags: --cfg target_vendor
+//@ [target_has_atomic]compile-flags: --cfg target_has_atomic="32"
+//@ [target_has_atomic_equal_alignment]compile-flags: --cfg target_has_atomic_equal_alignment="32"
+//@ [target_has_atomic_load_store]compile-flags: --cfg target_has_atomic_load_store="32"
+//@ [target_thread_local]compile-flags: --cfg target_thread_local
+//@ [relocation_model]compile-flags: --cfg relocation_model="a"
+
+
+fn main() {}

tests/ui/cfg/disallowed-cli-cfgs.target_abi.stderr

@@ -0,0 +1,5 @@
+error: unexpected `--cfg target_abi` flag
+   |
+   = note: config `target_abi` is only supposed to be controlled by `--target`
+   = note: see <https://github.com/rust-lang/rust/issues/xxxxx> for more information
+