I am just starting to use rust. I have installed rust with cargo and subsequently installed some packages, so that now ~/.cargo/registry/cache/github.com-1ecc6299db9ec823 folder has many crates:
aho-corasick-0.5.3.crate env_logger-0.4.3.crate open-1.2.2.crate regex-0.1.80.crate textwrap-0.11.0.crate
aho-corasick-0.6.10.crate gcc-0.3.55.crate rand-0.3.23.crate regex-0.2.11.crate thread-id-2.0.0.crate
aho-corasick-0.7.3.crate getrandom-0.1.2.crate rand-0.4.6.crate regex-1.1.6.crate thread_local-0.2.7.crate
ansi_term-0.11.0.crate hoedown-6.0.0.crate rand-0.6.5.crate regex-syntax-0.3.9.crate thread_local-0.3.6.crate
atty-0.2.11.crate itertools-0.5.10.crate rand_chacha-0.1.1.crate regex-syntax-0.5.6.crate time-0.1.42.crate
autocfg-0.1.2.crate kernel32-sys-0.2.2.crate rand_core-0.3.1.crate regex-syntax-0.6.6.crate toml-0.2.1.crate
bitflags-0.5.0.crate lazy_static-0.2.11.crate rand_core-0.4.0.crate rustc-serialize-0.3.24.crate ucd-util-0.1.3.crate
bitflags-1.0.4.crate lazy_static-1.3.0.crate rand_hc-0.1.0.crate rustc_version-0.1.7.crate unicode-width-0.1.5.crate
cargo-script-0.2.8.crate libc-0.2.51.crate rand_isaac-0.1.1.crate semver-0.1.20.crate utf8-ranges-0.1.3.crate
cfg-if-0.1.7.crate log-0.3.9.crate rand_jitter-0.1.3.crate semver-0.5.1.crate utf8-ranges-1.0.2.crate
chan-0.1.23.crate log-0.4.6.crate rand_os-0.1.3.crate semver-parser-0.6.2.crate vec_map-0.8.1.crate
clap-2.33.0.crate memchr-0.1.11.crate rand_pcg-0.1.2.crate shaman-0.1.0.crate winapi-0.2.8.crate
either-1.5.2.crate memchr-2.2.0.crate rand_xorshift-0.1.1.crate strsim-0.8.0.crate winapi-build-0.1.1.crate
I now want to use rustc command with -L option for a simple source file from here:
extern crate regex;
use regex::Regex;
fn main() {
let re = Regex::new(r"^\d{4}-\d{2}-\d{2}$").unwrap();
println!("Did our date match? {}", re.is_match("2014-01-01"));
}
However, this fails with following error:
$ rustc -L ~/.cargo/registry/cache/github.com-1ecc6299db9ec823 hellomain.rs
error[E0463]: can't find crate for `regex`
--> hellomain.rs:4:1
|
4 | extern crate regex;
| ^^^^^^^^^^^^^^^^^^^ can't find crate
error: aborting due to previous error
For more information about this error, try `rustc --explain E0463`.
Why is rustc not finding crate and how can this be corrected? Thanks for your help.
Edit: same error occurs even if I specify the crate file name:
$ rustc -L ~/.cargo/registry/cache/github.com-1ecc6299db9ec823/regex-1.1.6.crate hellomain.rs
error[E0463]: can't find crate for `regex`
--> hellomain.rs:4:1
|
4 | extern crate regex;
| ^^^^^^^^^^^^^^^^^^^ can't find crate
error: aborting due to previous error
For more information about this error, try `rustc --explain E0463`.
The .crate files you are trying to link to are not compiled binary artifacts. The format is (as far as I know) just a .gz of the crate's source code. It is the output format of cargo package. Also the -L flag typically is for library directories and -l is used for particular libraries to link (though you'll see below that rustc uses --extern for Rust dependencies).
In order to use the regex crate it must first be built. However as of now, it requires two other crates, regex_syntax and regex_automata, which need to be built first. Each one requires a rustc call separately, building off of each other, until you can finally build your executable.
Here are all those commands (using ./deps as build cache):
rustc --out-dir ./deps --crate-type lib --emit=metadata,link --crate-name regex_syntax --edition=2021 ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/regex-syntax-0.8.4/src/lib.rs
rustc --out-dir ./deps --crate-type lib --emit=metadata,link --crate-name regex_automata --edition=2021 ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/regex-automata-0.4.7/src/lib.rs --cfg 'feature="alloc"' --cfg 'feature="meta"' --cfg 'feature="nfa-pikevm"' --cfg 'feature="nfa-thompson"' --cfg 'feature="syntax"' -L dependency=./deps --extern regex_syntax=./deps/libregex_syntax.rmeta
rustc --out-dir ./deps --crate-type lib --emit=metadata,link --crate-name regex --edition=2021 ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/regex-1.10.5/src/lib.rs -L dependency=./deps --extern regex_automata=./deps/libregex_automata.rmeta --extern regex_syntax=./deps/libregex_syntax.rmeta
rustc --out-dir ./deps --crate-type bin --emit=link --crate-name mycrate --edition=2021 src/main.rs -L dependency=./deps --extern regex=./deps/libregex.rlib
This actually doesn't successfully run your code since I didn't include the 17 feature flags that the regex crate enables by default.
Running rustc commands manually like this assumes the sources are already available somewhere like in ~/.cargo/registry. This also doesn't specify optimization flags or codegen options. This neglects generating debug info. This also doesn't handle conflicts if two versions of the same crate both need to be built and linked. This also requires you to understand and propagate feature unification yourself. This also neglects all the environment variables that are passed by cargo during the compilation which some crates depend on.
This obviously gets more complicated as you depend on more crates and worse if there are build scripts. You can use cargo build -vv to see the normally generated commands. Just use cargo.