rustdoc: fix --emit=dep-info on scraped examples

[notriddle]

Makes sure both stages (the scraping process itself, and the doc build) emit complete dependency lists.

CC #146220
Part of #83784

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[jieyouxu]

r? rustdoc

[GuillaumeGomez]

Thanks!

@bors r+ rollup

[bors]

📌 Commit 8611f0b has been approved by GuillaumeGomez

It is now in the queue for this repository.

[fmease]

Failed in rollup: #148308 (comment) (job: aarch64-msvc-1)
@bors r-

[notriddle]

foobar.d: rustdoc\ex.calls src/lib.rs

rustdoc\ex.calls:
src/lib.rs:

Does anybody know whether it's okay to use backslashes in these dep files? Should I fix the test, or the emitter?

[notriddle]

Lacking any other resource to work with, I checked Cargo's dep info parser and the GNU Make docs. Both of these seem to imply that backslashes are fine, as long as they don't immediately precede a special character (like another backslash, a newline, or an asterisk):

https://doc.rust-lang.org/1.91.0/nightly-rustc/src/cargo/core/compiler/fingerprint/dep_info.rs.html#401-418

        } else if let Some(pos) = line.find(": ") {
            if found_deps {
                continue;
            }
            found_deps = true;
            let mut deps = line[pos + 2..].split_whitespace();

            while let Some(s) = deps.next() {
                let mut file = s.to_string();
                while file.ends_with('\\') {
                    file.pop();
                    file.push(' ');
                    file.push_str(deps.next().ok_or_else(|| {
                        crate::util::internal("malformed dep-info format, trailing \\")
                    })?);
                }
                ret.files.entry(file.into()).or_default();
            }

https://www.gnu.org/software/make/manual/make.html#Wildcard-Pitfall

Microsoft operating systems (MS-DOS and MS-Windows) use backslashes to separate directories in pathnames, like so:

  c:\foo\bar\baz.c

This is equivalent to the Unix-style c:/foo/bar/baz.c (the c: part is the so-called drive letter). When make runs on these systems, it supports backslashes as well as the Unix-style forward slashes in pathnames.

[notriddle]

@rustbot ready

[GuillaumeGomez]

Please note that / work in windows paths as well.

[notriddle]

Is there anything I need to change about this code?