This is to help with #9930
Example changes:
```diff
-[LOCKING] 4 packages
+[LOCKING] 4 packages to latest version
-[LOCKING] 2 packages
+[LOCKING] 2 packages to latest Rust 1.60.0 compatible versions
-[LOCKING] 2 packages
+[LOCKING] 2 packages to earliest versions
```
Benefits
- The package count is of "added" packages and this makes that more
logically clear
- This gives users transparency into what is happening, especially with
- what rust-version is use
- the transition to this feature in the new edition
- whether the planned config was applied or not (as I don't want it to
require an MSRV bump)
- Will make it easier in tests to show what changed
- Provides more motiviation to show this message in `cargo update` and
`cargo install` (that will be explored in a follow up PR)
This does come at the cost of more verbose output but hopefully not too
verbose. This is why I left off other factors, like avoid-dev-deps.
In #9930, it recommended improving the error for incompatible packages
so people can better get to the root of the problem.
For example, you might get an error about `clap_lex` but resolving the
error for the higher level `clap` could make the problem with `clap_lex`
go away.
Because I generally saw earlier packages in the graph reported, I
assumed we were reporting these errors bottom up.
It turns out, we are reporting them in the `UnitGraph`s order, which is
non-deterministic because it is built on a `HashMap`.
So this adds determinism and shows all incompatible dependencies
(not just the bottom or the root).
This is a first step.
We might find that we still want to only include the shallowest units,
rather than all.
At that point, we can add the complexity to address this by walking the
unit graph.
We could also further improve this by querying the index to suggest
compatible versions of packages.
This is another experiment for #9930.
Comparing preferring over exclusively using MSRV compatible:
Benefits
- Better error messages
- `--ignore-rust-version` is implicitly sticky
Downsides
- Can't backtrack for MSRV compatible version
- Still requires workspace-wide MSRV (compared to our desired end state of declaring MSRV as yet another dependency)
This builds on #12930
Generally, cargo avoids positional arguments. Mostly for the commands
that might forward arguments to another command, like `cargo test`.
It also allows some flexibility in turning flags into options.
For `cargo add` and `cargo remove`, we decided to accept positionals
because the motivations didn't seem to apply as much (similar to `cargo
install`).
This applies the pattern to `cargo update` as well which is in the same
category of commands as `cargo add` and `cargo remove`.
As for `--help` formatting, I'm mixed on whether `[SPEC]...` should be at the top like
other positionals or should be relegated to "Package selection". I went
with the latter mostly to make it easier to visualize the less common
choice.
Switching to a positional for `cargo update` (while keeping `-p` for
backwards compatibility) was referenced in #12425.
Packages in the local workspace can't get updated this way; the user
just needs to point to a different source, or otherwise update the
package themselves.
People encountering a dependency with a newer `rust-version` requirement
may not know about `cargo update --precise`, or may consider alternate
approaches that may be harmful (such as pinning with a `=` dependency).
Provide specific guidance in the error message.
If the user is using `cargo install`, suggest `cargo install --locked` instead.
Ed Page
Scott Schafer
Josh Triplett
Dirkjan Ochtman