Test that env! works with incremental compilation

This currently works because it's part of expansion, and that isn't yet
tracked by the query system. But we want to ensure it continues working,
even if that is changed.

tests/incremental/env/env_macro.rs

@@ -0,0 +1,18 @@
+// Check that changes to environment variables are propagated to `env!`.
+//
+// This test is intentionally written to not use any `#[cfg(rpass*)]`, to
+// _really_ test that we re-compile if the environment variable changes.
+
+//@ revisions: cfail1 rpass2 rpass3 cfail4
+//@ [cfail1]unset-rustc-env:EXAMPLE_ENV
+//@ [rpass2]rustc-env:EXAMPLE_ENV=one
+//@ [rpass2]exec-env:EXAMPLE_ENV=one
+//@ [rpass3]rustc-env:EXAMPLE_ENV=two
+//@ [rpass3]exec-env:EXAMPLE_ENV=two
+//@ [cfail4]unset-rustc-env:EXAMPLE_ENV
+
+fn main() {
+    assert_eq!(env!("EXAMPLE_ENV"), std::env::var("EXAMPLE_ENV").unwrap());
+    //[cfail1]~^ ERROR environment variable `EXAMPLE_ENV` not defined at compile time
+    //[cfail4]~^^ ERROR environment variable `EXAMPLE_ENV` not defined at compile time
+}

tests/incremental/env/option_env_macro.rs

@@ -0,0 +1,18 @@
+// Check that changes to environment variables are propagated to `option_env!`.
+//
+// This test is intentionally written to not use any `#[cfg(rpass*)]`, to
+// _really_ test that we re-compile if the environment variable changes.
+
+//@ revisions: rpass1 rpass2 rpass3 rpass4
+//@ [rpass1]unset-rustc-env:EXAMPLE_ENV
+//@ [rpass1]unset-exec-env:EXAMPLE_ENV
+//@ [rpass2]rustc-env:EXAMPLE_ENV=one
+//@ [rpass2]exec-env:EXAMPLE_ENV=one
+//@ [rpass3]rustc-env:EXAMPLE_ENV=two
+//@ [rpass3]exec-env:EXAMPLE_ENV=two
+//@ [rpass4]unset-rustc-env:EXAMPLE_ENV
+//@ [rpass4]unset-exec-env:EXAMPLE_ENV
+
+fn main() {
+    assert_eq!(option_env!("EXAMPLE_ENV"), std::env::var("EXAMPLE_ENV").ok().as_deref());
+}