Bump the MSRV to 1.64.0

[Rustin170506]

If the rust toolchain lower than v1.64.0 then you will get a compile error:

error[E0106]: missing lifetime specifier
  --> /Users/hi-rustin/.cargo/registry/src/github.com-1ecc6299db9ec823/inferno-0.11.15/src/flamegraph/color/mod.rs:83:25
   |
83 |     pub const VARIANTS: &[&'static str] = &[
   |                         ^ expected named lifetime parameter
   |
help: consider using the `'static` lifetime
   |
83 |     pub const VARIANTS: &'static [&'static str] = &[
   |                          +++++++
help: consider introducing a named lifetime parameter
   |
81 ~ impl<'a> Palette {
82 |     /// The valid set of palettes (via `FromStr`).
83 ~     pub const VARIANTS: &'a [&'static str] = &[

[Rustin170506]

Also, you can see an error for other packages:

error: package `rayon-core v1.11.0` cannot be built because it requires rustc 1.59 or newer, while the currently active rustc version is 1.56.1
Error: The process '/home/runner/.cargo/bin/cargo' failed with exit code 101

See: https://github.com/tikv/pprof-rs/actions/runs/4474804380/jobs/7863621636

error: package `prost v0.11.8` cannot be built because it requires rustc 1.60 or newer, while the currently active rustc version is 1.56.1
Error: The process '/home/runner/.cargo/bin/cargo' failed with exit code 101

See: https://github.com/tikv/pprof-rs/actions/runs/4474804380/jobs/7863622817?pr=204

[Rustin170506]

I am not sure does it make sense to keep or remove it. @YangKeao Could you please explain a bit why we use different Cargo.toml in CI and codebase? Thanks! It is a little bit confusing to have different Cargo.toml in the same project.

[Rustin170506]

For example:
Cargo always uses inferno 0.11.15 when building pprof-rs. You have to use cargo update -p inferno --precise 0.11.1 to work around.

[Rustin170506]

Another example:

➜  vsc cargo new --bin pporf-rs-test
     Created binary (application) `pporf-rs-test` package
➜  vsc cd pporf-rs-test
➜  pporf-rs-test git:(master) ✗ cargo add pprof -F flamegraph
    Updating crates.io index
➜  pporf-rs-test git:(master) ✗ cargo b
error[E0106]: missing lifetime specifier
  --> /Users/hi-rustin/.cargo/registry/src/github.com-1ecc6299db9ec823/inferno-0.11.15/src/flamegraph/color/mod.rs:83:25
   |
83 |     pub const VARIANTS: &[&'static str] = &[
   |                         ^ expected named lifetime parameter
   |
help: consider using the `'static` lifetime
   |
83 |     pub const VARIANTS: &'static [&'static str] = &[
   |                          +++++++
help: consider introducing a named lifetime parameter
   |
81 ~ impl<'a> Palette {
82 |     /// The valid set of palettes (via `FromStr`).
83 ~     pub const VARIANTS: &'a [&'static str] = &[
   |

My toolchain:

active toolchain
----------------

1.60.0-aarch64-apple-darwin (directory override for '/Users/hi-rustin/vsc/pporf-rs-test')
rustc 1.60.0 (7737e0b5c 2022-04-04)

[YangKeao]

Could you please explain a bit why we use different Cargo.toml in CI and codebase? Thanks! It is a little bit confusing to have different Cargo.toml in the same project.

For the MSRV actually. It proved pprof-rs can actually work on 1.56 with some dependency specified, so this only modified the dependencies for CI with 1.56 rust.

I'm not sure whether the dependencies of pprof-rs will be automatically updated when running cargo update -p pprof. If not, this behavior enables the user to update pprof-rs even when they are on 1.56 rust. (Even if not, it's also possible for them to downgrade the dependencies of pprof-rs to solve this problem)

[Rustin170506]

For the MSRV actually. It proved pprof-rs can actually work on 1.56 with some dependency specified, so this only modified the dependencies for CI with 1.56 rust.

Got it. Then probably the better solution is we set the correct version in the Cargo.toml instead of letting the user manually downgrade the deps of pprof-rs.

[Rustin170506]

Because there are some deps of pprof-rs that require a higher rust toolchain to build it. And Cargo does not consider the rust-version of Cargo.toml when it resolves the deps.

[Rustin170506]

instead of letting the user manually downgrade the deps of pprof-rs.

And there are no tips for users to work around this issue.

[YangKeao]

Got it. Then probably the better solution is we set the correct version in the Cargo.toml instead of letting the user manually downgrade the deps of pprof-rs.

I also don't want to specify a too low version (of dependencies) for users, because it will avoid the users from using newer dependencies. It cloud also cause the dependency conflict, so I usually use x.y but not x.y.z in most cases. Do you have any better idea on this? (Upgrading MSRV can be a choice, but it's actually avoidable, by specifying dependencies manually 🤦 .)

And Cargo does not consider the rust-version of Cargo.toml when it resolves the deps.

This is exactly the problem. The cargo will not automatically choose the newest valid version. As a developer of library, I also cannot specify different dependencies for different rust version.

Because there are some deps of pprof-rs that require a higher rust toolchain to build it.

All of them are here: inferno and criterion. And the solution is to downgrade them (by the user manually, as shown in the github.yml). The lower version are allowed in the range specified in Cargo.toml of pprof-rs. The sed in ci only sets the version precisely (from x.y to x.y.z).

[YangKeao]

And there are no tips for users to work around #204 (comment)

Yes 🤦 . I should add document for it.

[YangKeao]

LGTM

Though the MSRV increased passively, we have to accept it 😮‍💨

[Rustin170506]

Thanks for your review! 💚 💙 💜 💛 ❤️