error: linking with `cc` failed: exit code: 1

From your command rustc test1.rs the compiler infers the name of the executable should be test1. The linker tries to open this file so it can write the executable but fails with errno=21 whose stringified version is "Is a directory".

This suggests you have a directory in your working directory called test1 which is causing a conflict.

I was faced with three problems on Mac compiling Rust:

First: If you have any issue with writing files/dirs by ld just remove that files and try to recompile. I don't know why, but on Mac this issue happens time to time.

Second: If you have other ld errors (not about file access): try to add the following sections to your ~/.cargo/config (if you don't have this file feel free to create):

[target.x86_64-apple-darwin]
rustflags = [
  "-C", "link-arg=-undefined",
  "-C", "link-arg=dynamic_lookup",
]

[target.aarch64-apple-darwin]
rustflags = [
  "-C", "link-arg=-undefined",
  "-C", "link-arg=dynamic_lookup",
]

Third: Sometimes your Mac lack of some dev tools/dependencies. Install the most important of them automatically with the command:

xcode-select --install