Auto merge of rust-lang#9169 - Liberatys:emit-warning-on-env-variable…

…-case-mismatch, r=ehuss

Emit warning on env variable case mismatch

When running a command like `cargo --target TRIPPLE` cargo expects to find the environment variable CARGO_TARGET_[TRIPPLE]_* with uppercase and underscores. This check emits a warning if the checked environment variable has a mismatching case and/or contains dashes rather than underscores. The warning contains the given env variable as well as an explanation for the cause of the warning.

The check is skipped on windows as environment variables are treated as case insensitive on the platform.

Fixes rust-lang#8285

src/cargo/util/config/mod.rs

@@ -167,6 +167,8 @@ pub struct Config {
     target_dir: Option<Filesystem>,
     /// Environment variables, separated to assist testing.
     env: HashMap<String, String>,
+    /// Environment variables, converted to uppercase to check for case mismatch
+    upper_case_env: HashMap<String, String>,
     /// Tracks which sources have been updated to avoid multiple updates.
     updated_sources: LazyCell<RefCell<HashSet<SourceId>>>,
     /// Lock, if held, of the global package cache along with the number of
@@ -211,6 +213,15 @@ impl Config {
             })
             .collect();
 
+        let upper_case_env = if cfg!(windows) {
+            HashMap::new()
+        } else {
+            env.clone()
+                .into_iter()
+                .map(|(k, _)| (k.to_uppercase().replace("-", "_"), k))
+                .collect()
+        };
+
         let cache_rustc_info = match env.get("CARGO_CACHE_RUSTC_INFO") {
             Some(cache) => cache != "0",
             _ => true,
@@ -244,6 +255,7 @@ impl Config {
             creation_time: Instant::now(),
             target_dir: None,
             env,
+            upper_case_env,
             updated_sources: LazyCell::new(),
             package_cache_lock: RefCell::new(None),
             http_config: LazyCell::new(),
@@ -525,7 +537,10 @@ impl Config {
                     definition,
                 }))
             }
-            None => Ok(None),
+            None => {
+                self.check_environment_key_case_mismatch(key);
+                Ok(None)
+            }
         }
     }
 
@@ -545,9 +560,27 @@ impl Config {
                 return true;
             }
         }
+        self.check_environment_key_case_mismatch(key);
+
         false
     }
 
+    fn check_environment_key_case_mismatch(&self, key: &ConfigKey) {
+        if cfg!(windows) {
+            // In the case of windows the check for case mismatch in keys can be skipped
+            // as windows already converts its environment keys into the desired format.
+            return;
+        }
+
+        if let Some(env_key) = self.upper_case_env.get(key.as_env_key()) {
+            let _ = self.shell().warn(format!(
+                "Environment variables are expected to use uppercase letters and underscores, \
+                the variable `{}` will be ignored and have no effect",
+                env_key
+            ));
+        }
+    }
+
     /// Get a string config value.
     ///
     /// See `get` for more details.
@@ -640,7 +673,10 @@ impl Config {
     ) -> CargoResult<()> {
         let env_val = match self.env.get(key.as_env_key()) {
             Some(v) => v,
-            None => return Ok(()),
+            None => {
+                self.check_environment_key_case_mismatch(key);
+                return Ok(());
+            }
         };
 
         let def = Definition::Environment(key.as_env_key().to_string());

tests/testsuite/tool_paths.rs

@@ -353,6 +353,31 @@ fn custom_linker_env() {
         .run();
 }
 
+#[cargo_test]
+fn target_in_environment_contains_lower_case() {
+    let p = project().file("src/main.rs", "fn main() {}").build();
+
+    let target_keys = [
+        "CARGO_TARGET_X86_64_UNKNOWN_LINUX_musl_LINKER",
+        "CARGO_TARGET_x86_64_unknown_linux_musl_LINKER",
+    ];
+
+    for target_key in &target_keys {
+        let mut execs = p.cargo("build -v --target x86_64-unknown-linux-musl");
+        execs.env(target_key, "nonexistent-linker").with_status(101);
+        if cfg!(windows) {
+            execs.with_stderr_does_not_contain("warning:[..]");
+        } else {
+            execs.with_stderr_contains(format!(
+                "warning: Environment variables are expected to use uppercase letters and underscores, \
+                the variable `{}` will be ignored and have no effect",
+                target_key
+            ));
+        }
+        execs.run();
+    }
+}
+
 #[cargo_test]
 fn cfg_ignored_fields() {
     // Test for some ignored fields in [target.'cfg()'] tables.