chore(ci): remove clippy.sh

- Only one source of truth for lints, main Cargo.toml, making clippy.sh
  unnecessary.
- Warnings no longer denied, only in the CI. To preserve existing
  behaviors users can add `-Dwarnings` to local RUSTFLAGS.

We still need to enforce in workspace tests that all crates inherit
workspace lints.

Cargo.toml

@@ -251,13 +251,12 @@ void = "1.0.2"
 zstd = "0.13.1"
 
 [workspace.lints.rust]
-future-incompatible = "deny"
-nonstandard-style = "deny"
-rust-2018-idioms = "deny"
+future-incompatible = "warn"
+nonstandard-style = "warn"
+rust-2018-idioms = "warn"
 # See [here](https://github.com/taiki-e/cargo-llvm-cov/issues/370) for a discussion on why this is
 # needed (from rust 1.80).
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(coverage_nightly)'] }
-warnings = "deny"
 
 [workspace.lints.clippy]
-as_conversions = "deny"
+as_conversions = "warn"

scripts/run_tests.py

@@ -25,11 +25,12 @@ class BaseCommand(Enum):
 
     def cmd(self, crates: Set[str]) -> List[str]:
         package_args = []
+        operands = ["--", "-Dwarning"]  # "--" must be the first element.
         for package in crates:
             package_args.extend(["--package", package])
 
         if self == BaseCommand.TEST:
-            return ["cargo", "test"] + package_args
+            return ["cargo", "test"] + package_args + operands
         elif self == BaseCommand.CODECOV:
             return [
                 "cargo",
@@ -40,14 +41,19 @@ def cmd(self, crates: Set[str]) -> List[str]:
                 "codecov.json",
             ] + package_args
         elif self == BaseCommand.RUSTFMT:
+            operands += ["--check"]
             fmt_args = package_args if len(package_args) > 0 else ["--all"]
-            return ["scripts/rust_fmt.sh"] + fmt_args + ["--", "--check"]
+            return ["scripts/rust_fmt.sh"] + fmt_args + operands
         elif self == BaseCommand.CLIPPY:
             clippy_args = package_args if len(package_args) > 0 else ["--workspace"]
-            return ["scripts/clippy.sh"] + clippy_args
+            return ["cargo", "clippy"] + clippy_args + operands
         elif self == BaseCommand.DOC:
             doc_args = package_args if len(package_args) > 0 else ["--workspace"]
-            return ["cargo", "doc", "-r", "--document-private-items", "--no-deps"] + doc_args
+            return (
+                ["cargo", "doc", "-r", "--document-private-items", "--no-deps"]
+                + doc_args
+                + operands
+            )
 
         raise NotImplementedError(f"Command {self} not implemented.")