Emit warning when there is no space between -o and arg

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

Author: xizheyin

compiler/rustc_driver_impl/src/lib.rs

@@ -1237,6 +1237,14 @@ pub fn handle_options(early_dcx: &EarlyDiagCtxt, args: &[String]) -> Option<geto
         return None;
     }
 
+    // To avoid confusion, emit warning if no space
+    // between `-o` and arg, e.g.`-optimize`, is applied, see issue #142812
+    if let Some(name) = matches.opt_str("o") {
+        if args.iter().any(|arg| arg.starts_with("-o") && !arg.starts_with("-o=") && arg.ne("-o")) {
+            early_dcx.early_warn(format!("option `-o {}` is applied", name));
+        }
+    }
+
     Some(matches)
 }
 

tests/run-make/option-output-no-space/main.rs

@@ -0,0 +1 @@
+fn main() {}

tests/run-make/option-output-no-space/rmake.rs

@@ -0,0 +1,12 @@
+// This test is to check if the warning is emitted when no space
+// between `-o` and arg is applied, see issue #142812
+use run_make_support::rustc;
+
+fn main() {
+    rustc()
+        .input("main.rs")
+        .arg("-optimize")
+        .run()
+        .assert_stderr_contains("warning: option `-o ptimize` is applied");
+    rustc().input("main.rs").arg("-o").arg("ptimize").run().assert_stderr_equals("");
+}

tests/ui/unpretty/avoid-crash.stderr

@@ -1,3 +1,5 @@
+warning: option `-o .` is applied
+
 error: failed to write `.` due to $ERROR_MESSAGE
 
 error: aborting due to 1 previous error