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| -rw-r--r-- | src/doc/unstable-book/src/compiler-flags/env.md | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/src/doc/unstable-book/src/compiler-flags/env.md b/src/doc/unstable-book/src/compiler-flags/env.md index df0547dd24b..56f804fcd0c 100644 --- a/src/doc/unstable-book/src/compiler-flags/env.md +++ b/src/doc/unstable-book/src/compiler-flags/env.md @@ -5,7 +5,10 @@ The tracking issue for this feature is: [#118372](https://github.com/rust-lang/r ------------------------ This option flag allows to specify environment variables value at compile time to be -used by `env!` and `option_env!` macros. +used by `env!` and `option_env!` macros. It also impacts `tracked_env::var` function +from the `proc_macro` crate. + +This information will be stored in the dep-info files. When retrieving an environment variable value, the one specified by `--env` will take precedence. For example, if you want have `PATH=a` in your environment and pass: @@ -20,6 +23,21 @@ Then you will have: assert_eq!(env!("PATH"), "env"); ``` +It will trigger a new compilation if any of the `--env` argument value is different. +So if you first passed: + +```bash +--env A=B --env X=12 +``` + +and then on next compilation: + +```bash +--env A=B +``` + +`X` value is different (not set) so the code will be re-compiled. + Please note that on Windows, environment variables are case insensitive but case preserving whereas `rustc`'s environment variables are case sensitive. For example, having `Path` in your environment (case insensitive) is different than using |