[crater] Make missing_fragment_specifier an unconditional error

[tgross35]

This was attempted in 1 then reverted in 2 because of fallout. Recently, this was made an edition-dependent error in 3.

Experiment with turning missing fragment specifiers an unconditional error again.

More context: #128006

r? @petrochenkov

[tgross35]

This is just to test the diagnostics, none of the possible code cleanup is included.

@petrochenkov please take a look when you get the chance and start crater if the change seems correct.

@bors try

[bors]

⌛ Trying commit c2492ec with merge 063c08d...

[bors]

☀️ Try build successful - checks-actions
Build commit: 063c08d (063c08dd8db6ff113bb809c130456f1781abe72c)

[petrochenkov]

@craterbot check

[craterbot]

👌 Experiment pr-128425 created and queued.
🤖 Automatically detected try build 063c08d
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-128425 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-128425 is completed!
📊 156 regressed and 2 fixed (487733 total)
📰 Open the full report.

⚠️ If you notice any spurious failure please add them to the blacklist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[tgross35]

rg 'missing fragment specifier' -l --stats in the logs reports 373 matches. The previous attempt in 2020 had 475 regressions per #76605, so that is slight improvement but not much.

Like the previous run, almost all of these (361) come from clap <= 2.20, based on a crude rg 'missing fragment specifier.*\n.*clap' -l --stats -U. Remaining 12:

build-fail/reg/sem/0.1.0/master#83dcdb3a5dad0ed1e3e1fadc848d3f7727b41aa5.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/master#83dcdb3a5dad0ed1e3e1fadc848d3f7727b41aa5.txt-[INFO] [stdout]    --> src/macros.rs:136:17
build-fail/reg/sem/0.1.0/master#83dcdb3a5dad0ed1e3e1fadc848d3f7727b41aa5.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/master#83dcdb3a5dad0ed1e3e1fadc848d3f7727b41aa5.txt-[INFO] [stdout]    --> src/macros.rs:136:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:136:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:136:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:121:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:136:17
build-fail/reg/sem/0.1.0/try#063c08dd8db6ff113bb809c130456f1781abe72c.txt-[INFO] [stdout]    --> src/macros.rs:136:17

We could let this simmer for a while with the new error in deps level (#128122) and/or the edition-dependent lint (#128006). I don't really know how to feel about these results because all of the relevant clap versions have been yanked for ~4 years, per clap-rs/clap#2076.

Requesting compiler feedback for how to proceed. Context: this was made an e2024 error in #128006, making it an error in all editions is being considered here.

@rustbot label +I-compiler-nominated

[wesleywiser]

Discussed briefly in the compiler team triage meeting. Given that nearly all regressions are on very old versions of clap and this has been a compatibility warning since 2017, we think it's reasonable to make this an unconditional error.

[tgross35]

Thanks for discussing this. I'll wait for the next beta branch so #128122 is on stable for at least a cycle, then continue pushing this forward.

[tgross35]

To reflect my above comment

@rustbot blocked

[apiraino]

@tgross35 friendly ping in case you still want to pursuit this (I think formally this is not blocked anymore)

@rustbot label -S-blocked