Make it case-insensitive in Windows environment and add examples

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

@@ -775,13 +775,29 @@ impl LocalFingerprint {
         key: K,
         envs: &BTreeMap<String, Option<OsString>>,
     ) -> LocalFingerprint {
-        let key = key.as_ref();
+        fn get_envs_case_insensitive(
+            key: &str,
+            envs: &BTreeMap<String, Option<OsString>>,
+        ) -> Option<OsString> {
+            let upper_case_key: String = key.to_uppercase();
+            for (k, v) in envs {
+                if k.to_uppercase().eq(&upper_case_key) {
+                    return v.to_owned();
+                }
+            }
+            None
+        }
+
+        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> = if cfg!(windows) {
+            get_envs_case_insensitive(key, envs)
+        } else {
+            envs.get(key).and_then(|v| v.to_owned())
+        }
+        .xor(env::var_os(key))
+        .and_then(|os_str| os_str.into_string().ok());
 
         LocalFingerprint::RerunIfEnvChanged { var, val }
     }

tests/testsuite/build_script_env.rs

@@ -20,13 +20,13 @@ fn rerun_if_env_changes_config() {
         .file(
             "build.rs",
             r#"
-                fn main() {
-                    println!("cargo:rerun-if-env-changed=FOO");
-                    if let Ok(foo) = std::env::var("FOO") {
-                        assert!(&foo != "bad");
-                    }
-                }
-            "#,
+fn main() {
+    println!("cargo:rerun-if-env-changed=FOO");
+    if let Ok(foo) = std::env::var("FOO") {
+        assert!(&foo != "bad");
+    }
+}
+"#,
         )
         .build();
 
@@ -48,12 +48,63 @@ 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();
+}
+
+#[cfg(windows)]
+#[cargo_test]
+fn rerun_if_env_changes_config_in_windows() {
+    let p = project()
+        .file("Cargo.toml", &basic_manifest("foo", "0.1.0"))
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            ".cargo/config.toml",
+            r#"
+                [env]
+                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");
+    }
+}
+"#,
+        )
+        .build();
+
+    p.cargo("check")
+        .with_stderr_data(str![[r#"
+[COMPILING] foo v0.1.0 ([ROOT]/foo)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]])
+        .run();
+
+    p.change_file(
+        ".cargo/config.toml",
+        r#"
+            [env]
+            FoO = "bad"
+        "#,
+    );
+
+    p.cargo("check")
+        .with_status(101)
+        .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();
 }