Emit warning when there is no space between `-o` and arg #143719

xizheyin · 2025-07-10T06:22:37Z

getopt doesn't seem to have an API to check this, so we have to check the args manually.

r? compiler

rustbot · 2025-07-10T06:22:45Z

This PR modifies run-make tests.

jieyouxu

This seems reasonable, though I can imagine this might be a bit annoying. I'll defer to @wesleywiser for a second opinion.

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

jieyouxu · 2025-07-10T06:26:07Z

r? @wesleywiser (re. #142812)

rustbot · 2025-07-10T06:26:13Z

wesleywiser is not on the review rotation at the moment.
They may take a while to respond.

jieyouxu · 2025-07-10T06:26:43Z

Ah right. I'll wait a bit in case Wesley has feedback.
r? jieyouxu

jieyouxu · 2025-07-10T06:31:42Z

compiler/rustc_driver_impl/src/lib.rs

+    // 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));
+        }
+    }


Suggestion: if we're going to emit this warning, can you also include a bit more context on why this is warned on in the first place and how users can address this warning? I.e. for the wording, I suggest

warning: option `-o` has no space between flag name and value, which can be confusing help: option `-o {}` is applied instead of a flag named `o{}` help: if you meant to specify output filename `{}`, write `-o {}` instead

Suggestion: also, maybe remark this case in the rustc book on compiler flags.

Good suggestions, I will finish this later.

You might want to hold off on changing this for a moment, still discussing formulation of this warning in the linked thread

jieyouxu · 2025-07-10T06:47:15Z

Asking for some more opinions about if warning on -ofilename might be too annoying. Let's give it sometime for the vibecheck, flip this to review / ping me by next thursday (2025-07-17) if we don't have a resolution by then yet.

cf. #t-compiler > Warn on `-ofilename`/`-Lpath` without space

@rustbot label: -S-waiting-on-review +S-waiting-on-team

xizheyin · 2025-07-11T09:53:59Z

Now, it prints like this

$ rustc +stage1 src/main.rs -optimize
warning: option `-o` has no space between flag name and value, which can be confusing

note: option `-o ptimize` is applied instead of a flag named `optimize` to specify output filename `ptimize`

$ rustc +stage1 src/main.rs -out-dir
warning: option `-o` has no space between flag name and value, which can be confusing

note: option `-o ut-dir` is applied instead of a flag named `out-dir` to specify output filename `ut-dir`

note: Do you mean `--out-dir`?

$ rustc +stage1 src/main.rs -overflow-checks
warning: option `-o` has no space between flag name and value, which can be confusing

note: option `-o verflow-checks` is applied instead of a flag named `overflow-checks` to specify output filename `verflow-checks`

note: Do you mean `-C overflow_checks`?

$ rustc +stage1 src/main.rs -overflow_checks
warning: option `-o` has no space between flag name and value, which can be confusing

note: option `-o verflow_checks` is applied instead of a flag named `overflow_checks` to specify output filename `verflow_checks`

note: Do you mean `-C overflow_checks`?

$ rustc +stage1 src/main.rs -o3
warning: option `-o` has no space between flag name and value, which can be confusing

note: option `-o 3` is applied instead of a flag named `o3` to specify output filename `3`

xizheyin

@rustbot ready

jieyouxu

Thanks, some thoughts. Mostly to make this even more conservative.

compiler/rustc_driver_impl/src/lib.rs

compiler/rustc_driver_impl/src/args.rs

jieyouxu · 2025-07-15T02:41:46Z

compiler/rustc_driver_impl/src/args.rs

+    for option in optgroups {
+        let prefix = String::from("--");
+        if starts_with_ignoring_separators(option.long_name(), suspect) {
+            return Some(prefix + option.long_name());
+        }
+    }


Suggestion: I would also not bother with e.g. --oprint

Currently, -oprint won't emit a warning, do you mean we should emit a warning?

Hm, I'm not sure what I meant by this, I meant we should not.

Yes, that's the way it is now. it match oprint which does not exist in rustc option group.

compiler/rustc_driver_impl/src/lib.rs

jieyouxu · 2025-07-15T02:54:13Z

@rustbot author

rustbot · 2025-07-15T02:54:17Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

Signed-off-by: xizheyin <[email protected]>

xizheyin · 2025-07-16T15:42:26Z

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

+// This test is to check if the warning is emitted when no space
+// between `-o` and arg is applied, see issue #142812
+
+//@ ignore-cross-compile
+use run_make_support::rustc;


Oh, I see now. I added it on top of the test,

jieyouxu · 2025-07-16T15:47:06Z

@bors r+

bors · 2025-07-16T15:47:09Z

📌 Commit af39c0c has been approved by jieyouxu

It is now in the queue for this repository.

rustbot assigned jieyouxu Jul 10, 2025

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 10, 2025

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xizheyin force-pushed the 142812-1 branch from 98e5c53 to 9bacaf7 Compare July 10, 2025 06:29

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xizheyin force-pushed the 142812-1 branch from 9bacaf7 to 0cd9eda Compare July 11, 2025 09:49

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

af39c0c

Signed-off-by: xizheyin <[email protected]>

xizheyin force-pushed the 142812-1 branch from 2110bc1 to af39c0c Compare July 16, 2025 15:41

xizheyin commented Jul 16, 2025

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Rollup of 11 pull requests #144109

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bors merged commit 26f5936 into rust-lang:master Jul 18, 2025
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rustbot added this to the 1.90.0 milestone Jul 18, 2025

xizheyin deleted the 142812-1 branch July 21, 2025 14:21

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Emit warning when there is no space between -o and arg #143719

Emit warning when there is no space between -o and arg #143719

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Emit warning when there is no space between `-o` and arg #143719

Emit warning when there is no space between `-o` and arg #143719

xizheyin commented Jul 10, 2025 •

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