feat: Support variable substitution in VSCode settings
Currently support a subset of [variables provided by VSCode](https://code.visualstudio.com/docs/editor/variables-reference) in `server.extraEnv` section of Rust-Analyzer settings:
* `workspaceFolder`
* `workspaceFolderBasename`
* `cwd`
* `execPath`
* `pathSeparator`
Also, this PR adds support for general environment variables resolution. You can declare environment variables and reference them from other variables like this:
```JSON
"rust-analyzer.server.extraEnv": {
"RUSTFLAGS": "-L${env:OPEN_XR_SDK_PATH}",
"OPEN_XR_SDK_PATH": "${workspaceFolder}\\..\\OpenXR-SDK\\build\\src\\loader\\Release"
},
```
The order of variable declaration doesn't matter, you can reference variables before defining them. If the variable is not present in `extraEnv` section, VSCode will search for them in your environment. Missing variables will be replaced with empty string. Circular references won't be resolved and will be passed to rust-analyzer server process as is.
Closes#9626, but doesn't address use cases where people want to use values provided by `rustc` or `cargo`, such as `${targetTriple}` proposal #11649
First, we go through every environment variable key and record all cases
where there are reference to other variables / dependencies.
We track two sets of variables - resolved and yet-to-be-resolved.
We pass over a list of variables over and over again and when all
variable's dependencies were resolved during previous passes we perform
a replacement for that variable, too.
Over time the size of `toResolve` set should go down to zero, however
circular dependencies may prevent that. We track the size of `toResolve`
between iterations to avoid infinite looping.
At the end we produce an object of the same size and shape as
the original, but with the values replace with resolved versions.
Assuming ID=linux in isNixOs by default. You can get away with
default "", but why do that if there's a default value in spec?)
Also removed toLowerCase — it really shouldn't be needed.
Fixes#11709
Lukas Wirth