Use better heuristic for printing Cargo specific diagnostics

compiler/rustc_codegen_ssa/src/errors.rs

@@ -362,8 +362,11 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for LinkingFailed<'_> {
  // which by now we have no way to translate.
  if contains_undefined_ref {
  diag.note(fluent::codegen_ssa_extern_funcs_not_found)
- .note(fluent::codegen_ssa_specify_libraries_to_link)
- .note(fluent::codegen_ssa_use_cargo_directive);
+ .note(fluent::codegen_ssa_specify_libraries_to_link);
+
+ if rustc_session::utils::was_invoked_from_cargo() {
+ diag.note(fluent::codegen_ssa_use_cargo_directive);
+ }
  }
  diag
  }

compiler/rustc_hir_typeck/src/errors.rs

@@ -293,7 +293,7 @@ pub enum HelpUseLatestEdition {
 impl HelpUseLatestEdition {
  pub fn new() -> Self {
  let edition = LATEST_STABLE_EDITION;
- if std::env::var_os("CARGO").is_some() {
+ if rustc_session::utils::was_invoked_from_cargo() {
  Self::Cargo { edition }
  } else {
  Self::Standalone { edition }

compiler/rustc_incremental/src/persist/fs.rs

@@ -492,7 +492,7 @@ fn lock_directory(
  lock_err,
  session_dir,
  is_unsupported_lock,
- is_cargo: std::env::var_os("CARGO").map(|_| ()),
+ is_cargo: rustc_session::utils::was_invoked_from_cargo().then_some(()),
  }))
  }
  }

compiler/rustc_lint/src/context/diagnostics.rs

@@ -205,7 +205,7 @@ pub(super) fn builtin(
  Vec::new()
  };
 
- let is_from_cargo = std::env::var_os("CARGO").is_some();
+ let is_from_cargo = rustc_session::utils::was_invoked_from_cargo();
  let mut is_feature_cfg = name == sym::feature;
 
  if is_feature_cfg && is_from_cargo {
@@ -340,7 +340,7 @@ pub(super) fn builtin(
  .copied()
  .flatten()
  .collect();
- let is_from_cargo = std::env::var_os("CARGO").is_some();
+ let is_from_cargo = rustc_session::utils::was_invoked_from_cargo();
 
  // Show the full list if all possible values for a given name, but don't do it
  // for names as the possibilities could be very long

compiler/rustc_parse/src/errors.rs

@@ -2545,7 +2545,7 @@ pub enum HelpUseLatestEdition {
 impl HelpUseLatestEdition {
  pub fn new() -> Self {
  let edition = LATEST_STABLE_EDITION;
- if std::env::var_os("CARGO").is_some() {
+ if rustc_session::utils::was_invoked_from_cargo() {
  Self::Cargo { edition }
  } else {
  Self::Standalone { edition }

compiler/rustc_session/src/utils.rs

@@ -1,7 +1,10 @@
 use crate::session::Session;
 use rustc_data_structures::profiling::VerboseTimingGuard;
 use rustc_fs_util::try_canonicalize;
-use std::path::{Path, PathBuf};
+use std::{
+ path::{Path, PathBuf},
+ sync::OnceLock,
+};
 
 impl Session {
  pub fn timer(&self, what: &'static str) -> VerboseTimingGuard<'_> {
@@ -158,3 +161,18 @@ pub fn extra_compiler_flags() -> Option<(Vec<String>, bool)> {
 
  if !result.is_empty() { Some((result, excluded_cargo_defaults)) } else { None }
 }
+
+/// Returns whenever rustc was launched by Cargo as opposed to another build system.
+///
+/// To be used in diagnostics to avoid printing Cargo specific suggestions to other
+/// build systems (like Bazel, Buck2, Makefile, ...).
+pub fn was_invoked_from_cargo() -> bool {
+ static FROM_CARGO: OnceLock<bool> = OnceLock::new();
+
+ // To be able to detect Cargo, we use the simplest and least intrusive
+ // way: we check whenever the `CARGO_CRATE_NAME` env is set.
+ //
+ // Note that it is common in Makefiles to define the `CARGO` env even
+ // though we may not have been called by Cargo, so we avoid using it.
+ *FROM_CARGO.get_or_init(|| std::env::var_os("CARGO_CRATE_NAME").is_some())
+}

tests/ui/async-await/suggest-switching-edition-on-await-cargo.rs

@@ -1,4 +1,4 @@
-//@ rustc-env:CARGO=/usr/bin/cargo
+//@ rustc-env:CARGO_CRATE_NAME=foo
 
 use std::pin::Pin;
 use std::future::Future;

tests/ui/check-cfg/cargo-feature.rs

@@ -4,7 +4,7 @@
 //
 //@ check-pass
 //@ revisions: some none
-//@ rustc-env:CARGO=/usr/bin/cargo
+//@ rustc-env:CARGO_CRATE_NAME=foo
 //@ compile-flags: -Z unstable-options
 //@ [none]compile-flags: --check-cfg=cfg(feature,values())
 //@ [some]compile-flags: --check-cfg=cfg(feature,values("bitcode"))

tests/ui/check-cfg/diagnotics.rs

@@ -1,7 +1,7 @@
 //@ check-pass
 //@ revisions: cargo rustc
-//@ [rustc]unset-rustc-env:CARGO
-//@ [cargo]rustc-env:CARGO=/usr/bin/cargo
+//@ [rustc]unset-rustc-env:CARGO_CRATE_NAME
+//@ [cargo]rustc-env:CARGO_CRATE_NAME=foo
 //@ compile-flags: --check-cfg=cfg(feature,values("foo")) --check-cfg=cfg(no_values) -Z unstable-options
 
 #[cfg(featur)]

tests/ui/crate-loading/missing-std.rs

@@ -1,6 +1,6 @@
 //@ compile-flags: --target x86_64-unknown-uefi
 //@ needs-llvm-components: x86
-//@ rustc-env:CARGO=/usr/bin/cargo
+//@ rustc-env:CARGO_CRATE_NAME=foo
 #![feature(no_core)]
 #![no_core]
 extern crate core;