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

compiler/rustc_driver_impl/src/args.rs

@@ -1,6 +1,6 @@
 use std::{env, error, fmt, fs, io};
 
-use rustc_session::EarlyDiagCtxt;
+use rustc_session::{EarlyDiagCtxt, config};
 
 /// Expands argfiles in command line arguments.
 #[derive(Default)]
@@ -153,3 +153,40 @@ impl fmt::Display for Error {
 }
 
 impl error::Error for Error {}
+
+/// check if suspect is a confusables of any option or arg in rustc or fake_args
+pub(crate) fn check_confusables(suspect: &str, fake_args: &[&str]) -> Option<String> {
+    let suspect = suspect.strip_prefix("-").unwrap_or(suspect);
+    // Check if s1 starts with s2, ignoring hyphens vs underscores
+    fn starts_with_ignoring_separators(s1: &str, s2: &str) -> bool {
+        let normalized_s1 = s1.replace('-', "_");
+        let normalized_s2 = s2.replace('-', "_");
+        normalized_s1.starts_with(&normalized_s2)
+    }
+
+    let optgroups = config::rustc_optgroups();
+    for option in optgroups {
+        let prefix = String::from("--");
+        if starts_with_ignoring_separators(option.long_name(), suspect) {
+            return Some(prefix + option.long_name());
+        }
+    }
+    for option in config::CG_OPTIONS {
+        let prefix = String::from("-C ");
+        if starts_with_ignoring_separators(option.name(), suspect) {
+            return Some(prefix + option.name());
+        }
+    }
+    for option in config::Z_OPTIONS {
+        let prefix = String::from("-Z ");
+        if starts_with_ignoring_separators(option.name(), suspect) {
+            return Some(prefix + option.name());
+        }
+    }
+    for arg in fake_args {
+        if starts_with_ignoring_separators(arg, suspect) {
+            return Some("".to_string());
+        }
+    }
+    None
+}

compiler/rustc_driver_impl/src/lib.rs

@@ -103,6 +103,7 @@ mod signal_handler {
     pub(super) fn install() {}
 }
 
+use crate::args::check_confusables;
 use crate::session_diagnostics::{
     CantEmitMIR, RLinkEmptyVersionNumber, RLinkEncodingVersionMismatch, RLinkRustcVersionMismatch,
     RLinkWrongFileType, RlinkCorruptFile, RlinkNotAFile, RlinkUnableToRead, UnstableFeatureUsage,
@@ -1237,6 +1238,26 @@ 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`, `-out-dir`, is applied, see issue #142812
+    if let Some(name) = matches.opt_str("o")
+        && let Some(suspect) = args.iter().find(|arg| arg.starts_with("-o") && *arg != "-o")
+    {
+        let confusables = ["optimize", "o0", "o1", "o2", "o3", "ofast", "og", "os", "oz"];
+        if let Some(confusable) = check_confusables(&suspect, &confusables) {
+            early_dcx.early_warn(
+                "option `-o` has no space between flag name and value, which can be confusing",
+            );
+            early_dcx.early_note(format!(
+                "option `-o {}` is applied instead of a flag named `o{}` to specify output filename `{}`",
+                name, name, name
+            ));
+            if !confusable.is_empty() {
+                early_dcx.early_note(format!("Do you mean `{}`?", confusable));
+            }
+        }
+    }
+
     Some(matches)
 }
 

compiler/rustc_session/src/config.rs

@@ -1653,6 +1653,10 @@ impl RustcOptGroup {
             OptionKind::FlagMulti => options.optflagmulti(short_name, long_name, desc),
         };
     }
+
+    pub fn long_name(&self) -> &str {
+        self.long_name
+    }
 }
 
 pub fn make_opt(

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 +1,82 @@
+// 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() {
+    // test fake args
+    rustc()
+        .input("main.rs")
+        .arg("-optimize")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains(
+            "note: option `-o ptimize` is applied instead of a flag named `optimize`",
+        )
+        .assert_stderr_contains("to specify output filename `ptimize`");
+    rustc()
+        .input("main.rs")
+        .arg("-o0")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains("note: option `-o 0` is applied instead of a flag named `o0`")
+        .assert_stderr_contains("to specify output filename `0`");
+    rustc().input("main.rs").arg("-o1").run();
+    // test real args by iter optgroups
+    rustc()
+        .input("main.rs")
+        .arg("-out-dir")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains(
+            "note: option `-o ut-dir` is applied instead of a flag named `out-dir`",
+        )
+        .assert_stderr_contains("to specify output filename `ut-dir`")
+        .assert_stderr_contains("Do you mean `--out-dir`?");
+    // test real args by iter CG_OPTIONS
+    rustc()
+        .input("main.rs")
+        .arg("-opt-level")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains(
+            "note: option `-o pt-level` is applied instead of a flag named `opt-level`",
+        )
+        .assert_stderr_contains("to specify output filename `pt-level`")
+        .assert_stderr_contains("Do you mean `-C opt_level`?");
+    rustc()
+        .input("main.rs")
+        .arg("-overflow-checks")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains(
+            "note: option `-o verflow-checks` is applied instead of a flag named `overflow-checks`",
+        )
+        .assert_stderr_contains("to specify output filename `verflow-checks`")
+        .assert_stderr_contains("Do you mean `-C overflow_checks`?");
+    // test real args by iter Z_OPTIONS
+    rustc()
+        .input("main.rs")
+        .arg("-oom")
+        .run()
+        .assert_stderr_contains(
+            "warning: option `-o` has no space between flag name and value, which can be confusing",
+        )
+        .assert_stderr_contains("note: option `-o om` is applied instead of a flag named `oom`")
+        .assert_stderr_contains("to specify output filename `om`")
+        .assert_stderr_contains("note: Do you mean `-Z oom`?");
+
+    // test no warning when there is space between `-o` and arg
+    rustc().input("main.rs").arg("-o").arg("ptimize").run().assert_stderr_equals("");
+    rustc().input("main.rs").arg("--out-dir").arg("xxx").run().assert_stderr_equals("");
+    rustc().input("main.rs").arg("-o").arg("out-dir").run().assert_stderr_equals("");
+}