Make it case-insensitive in Windows environment and add examples

Author: heisen-li

src/cargo/core/compiler/fingerprint/mod.rs

@@ -775,13 +775,24 @@ impl LocalFingerprint {
         key: K,
         envs: &BTreeMap<String, Option<OsString>>,
     ) -> LocalFingerprint {
-        let key = key.as_ref();
+        fn get_env_value(key: &str, envs: &BTreeMap<String, Option<OsString>>) -> Option<OsString> {
+            if cfg!(windows) {
+                let upper_case_key: String = key.to_uppercase();
+                if let Some(v) = envs.get(&upper_case_key) {
+                    return v.to_owned();
+                }
+            }
+            env::var_os(key)
+        }
+
+        let key: &str = key.as_ref();
         let var = key.to_owned();
-        let val = envs
-            .get(key)
-            .map(|v| v.to_owned())
-            .or_else(|| Some(env::var_os(key)))
-            .and_then(|os_str| os_str?.into_string().ok());
+
+        let val: Option<String> = match envs.get(key) {
+            Some(v) => v.to_owned(),
+            None => get_env_value(key, envs),
+        }
+        .and_then(|os_str| os_str.into_string().ok());
 
         LocalFingerprint::RerunIfEnvChanged { var, val }
     }

tests/testsuite/build_script_env.rs

@@ -7,6 +7,27 @@ use cargo_test_support::str;
 
 #[cargo_test]
 fn rerun_if_env_changes_config() {
+    let build = if cfg!(windows) {
+        r#"
+fn main() {
+    println!("cargo:rerun-if-env-changed=fOO");
+    println!("aaaaaa");
+    if let Ok(foo) = std::env::var("Foo") {
+        assert!(&foo != "bad");
+    }
+}
+"#
+    } else {
+        r#"
+fn main() {
+    println!("cargo:rerun-if-env-changed=FOO");
+    if let Ok(foo) = std::env::var("FOO") {
+        assert!(&foo != "bad");
+    }
+}
+"#
+    };
+
     let p = project()
         .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
         .file("src/main.rs", "fn main() {}")
@@ -17,17 +38,7 @@ fn rerun_if_env_changes_config() {
                 FOO = "good"
             "#,
         )
-        .file(
-            "build.rs",
-            r#"
-                fn main() {
-                    println!("cargo:rerun-if-env-changed=FOO");
-                    if let Ok(foo) = std::env::var("FOO") {
-                        assert!(&foo != "bad");
-                    }
-                }
-            "#,
-        )
+        .file("build.rs", build)
         .build();
 
     p.cargo("check")
@@ -48,12 +59,11 @@ fn rerun_if_env_changes_config() {
 
     p.cargo("check")
         .with_status(101)
-        .with_stderr_data(
-            "\
+        .with_stderr_data(str![[r#"
 [COMPILING] foo v0.1.0 ([ROOT]/foo)
 [ERROR] failed to run custom build command for `foo v0.1.0 ([ROOT]/foo)`
-...",
-        )
+...
+"#]])
         .run();
 }