Avoid hashing CARGO_ variables that are redundant/unrelated

[kornelski]

Excludes more irrelevant/redundant CARGO_ variables based on a blocklist

(Another option could be to remove hashing of the CARGO_ variables completely — #2494)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.05%. Comparing base (1332701) to head (971b4e0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2495   +/-   ##
=======================================
  Coverage   71.05%   71.05%           
=======================================
  Files          64       64           
  Lines       35359    35364    +5     
=======================================
+ Hits        25124    25129    +5     
  Misses      10235    10235           

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[Xuanwo]

Thank you for this change!

[sylvestre]

would it be possible to have a test?

[sylvestre]

maybe something like:

Suggested change

	let may_skip = var == "CARGO_MAKEFLAGS" // will have jobserver info which is extremely non-cacheable.
	|| var == "CARGO_BUILD_JOBS" // does not affect results
	|| var.starts_with("CARGO_REGISTRIES_") // CARGO_REGISTRIES_*_TOKEN contains non-cacheable secrets, and package IDs already uniquely identify the relevant registries.
	|| var.starts_with("CARGO_REGISTRY_") // same as CARGO_REGISTRIES_*
	|| var == "CARGO_TARGET_DIR" // already included in the file paths
	|| var == "CARGO_BUILD_BUILD_DIR"
	|| var == "CARGO_BUILD_TARGET_DIR"
	|| var.starts_with("CARGO_HTTP_") // not relevant
	|| var.starts_with("CARGO_NET_")
	|| var.starts_with("CARGO_TERM_")
	|| var.starts_with("CARGO_ALIAS_")
	|| var == "CARGO_CACHE_AUTO_CLEAN_FREQUENCY";
	if may_skip {
	// Skip environment variables that shouldn't affect caching
	const CARGO_SKIP_VARS: &[&str] = &[
	"CARGO_MAKEFLAGS", // jobserver info which is extremely non-cacheable
	"CARGO_BUILD_JOBS", // does not affect results
	"CARGO_TARGET_DIR", // already included in the file paths
	"CARGO_BUILD_BUILD_DIR",
	"CARGO_BUILD_TARGET_DIR",
	"CARGO_CACHE_AUTO_CLEAN_FREQUENCY",
	];
	const CARGO_SKIP_PREFIXES: &[&str] = &[
	"CARGO_REGISTRIES_", // contains non-cacheable secrets, package IDs already identify registries
	"CARGO_REGISTRY_", // same as CARGO_REGISTRIES_*
	"CARGO_HTTP_", // not relevant
	"CARGO_NET_",
	"CARGO_TERM_",
	"CARGO_ALIAS_",
	];
	let may_skip = CARGO_SKIP_VARS.contains(&var.as_str())
	|| CARGO_SKIP_PREFIXES
	.iter()
	.any(|prefix| var.starts_with(prefix));
	if may_skip {