Rollup merge of #141413 - est31:cfg_version_env_var, r=jieyouxu

Make #[cfg(version)] respect RUSTC_OVERRIDE_VERSION_STRING

The `#[cfg(version(...))]` feature is currently under-tested. Part of it is the difficulty that it is hard to write a test that never changes, while the version of the Rust compiler indeed *does* change.

PR #81468 added the first and so far only test of `#[cfg(version(...))]`'s functionality (there is one other test for the *syntax*, that also acts as feature gate). But that test uses a proc macro that parses the version: the text of the test doesn't contain the actual `#[cfg(version(...))]`.

This PR makes `#[cfg(version(...))]` respect `RUSTC_OVERRIDE_VERSION_STRING`, added by PR #124339, allowing us to virtually pin the rustc version and write tests from all directions against some specific version.

The PR also adds a functional test of `#[cfg(version(...))]` that leverages `RUSTC_OVERRIDE_VERSION_STRING`.

Pulled out of #141137.

Tracking issue: #64796

2 files changed, 47 insertions, 0 deletions

diff --git a/tests/ui/cfg/cfg-version/cfg-version-expand.rs b/tests/ui/cfg/cfg-version/cfg-version-expand.rs
new file mode 100644
index 00000000000..8c426b4a41f
--- /dev/null
+++ b/tests/ui/cfg/cfg-version/cfg-version-expand.rs
@@ -0,0 +1,30 @@
+//@ run-pass
+//@ rustc-env:RUSTC_OVERRIDE_VERSION_STRING=1.50.3
+
+#![feature(cfg_version)]
+
+#[cfg(version("1.49.0"))]
+const ON_1_49_0: bool = true;
+#[cfg(version("1.50"))]
+const ON_1_50_0: bool = true;
+#[cfg(not(version("1.51")))]
+const ON_1_51_0: bool = false;
+
+// This one uses the wrong syntax, so doesn't eval to true
+#[warn(unexpected_cfgs)]
+#[cfg(not(version = "1.48.0"))] //~ WARN unexpected `cfg` condition name: `version`
+const ON_1_48_0: bool = false;
+
+fn main() {
+    assert!(!ON_1_48_0);
+    assert!(ON_1_49_0);
+    assert!(ON_1_50_0);
+    assert!(!ON_1_51_0);
+    assert!(cfg!(version("1.1")));
+    assert!(cfg!(version("1.49")));
+    assert!(cfg!(version("1.50.0")));
+    assert!(cfg!(version("1.50.3")));
+    assert!(!cfg!(version("1.50.4")));
+    assert!(!cfg!(version("1.51")));
+    assert!(!cfg!(version("1.100")));
+}
diff --git a/tests/ui/cfg/cfg-version/cfg-version-expand.stderr b/tests/ui/cfg/cfg-version/cfg-version-expand.stderr
new file mode 100644
index 00000000000..a9a8d86c0fa
--- /dev/null
+++ b/tests/ui/cfg/cfg-version/cfg-version-expand.stderr
@@ -0,0 +1,17 @@
+warning: unexpected `cfg` condition name: `version`
+  --> $DIR/cfg-version-expand.rs:15:11
+   |
+LL | #[cfg(not(version = "1.48.0"))]
+   |           ^^^^^^^^^^^^^^^^^^
+   |
+   = help: to expect this configuration use `--check-cfg=cfg(version, values("1.48.0"))`
+   = 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
+help: there is a similar config predicate: `version("..")`
+   |
+LL - #[cfg(not(version = "1.48.0"))]
+LL + #[cfg(not(version("1.48.0")))]
+   |
+
+warning: 1 warning emitted
+