Rollup merge of #121237 - Urgau:better-cargo-heuristic, r=compiler-errors

Use better heuristic for printing Cargo specific diagnostics

It was [reported](https://github.com/rust-lang/rust/issues/82450#issuecomment-1948574677) in the check-cfg call for testing that the Rust for Linux project is setting the `CARGO` env without compiling with it, which is an issue since we are using the `CARGO` env as a proxy for "was launched from Cargo".

This PR switch to the `CARGO_CRATE_NAME` [Cargo env](https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates), which shouldn't collide (as much) with other build systems. I also took the opportunity to consolidate all the checks under the same function.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 3c3a8d6fbb9..674f7218ea6 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/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 }