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feat(build): Add option to emit rerun-if-changed instructions #1021

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Jun 21, 2022
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feat(build): Add option to emit rerun-if-changed instructions #1021

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tonic-build: Add option to emit cargo:rerun-if-changed instructions
mickvangelderen Jun 17, 2022
f774465
tonic-build: Document default value for emit_rerun_if_changed
mickvangelderen Jun 20, 2022
8e64c55
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mickvangelderen Jun 20, 2022
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33 changes: 33 additions & 0 deletions tonic-build/src/prost.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ pub fn configure() -> Builder {
emit_package: true,
protoc_args: Vec::new(),
include_file: None,
emit_rerun_if_changed: std::env::var_os("CARGO").is_some(),
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@mickvangelderen mickvangelderen Jun 17, 2022 •
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Not sure if run-time detection of whether the code is run as a build script is

  1. right, and
  2. necessary

Setting it to true may constitute a breaking change if people are using tonic_build outside of build scripts.
We could also set it to false in this version of tonic_build and make it true or automatically detected in the next major release.

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I think its fine to set this for a build script. Do you know what other projects with similar features use? I don't mind auto enabling this in this release since I don't really think its a breaking style change etc.

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I skimmed through the cargo reference but did not find anything else. I also failed to find results for how to detect Rust code is being run from a build script through Google. I hope this does a good enough job.

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Yeah, it seems fine to me.

}
}

Expand Down Expand Up @@ -224,6 +225,7 @@ pub struct Builder {
pub(crate) compile_well_known_types: bool,
pub(crate) protoc_args: Vec<OsString>,
pub(crate) include_file: Option<PathBuf>,
pub(crate) emit_rerun_if_changed: bool,

out_dir: Option<PathBuf>,
}
Expand Down Expand Up @@ -368,6 +370,24 @@ impl Builder {
self
}

/// Enable or disable emitting
/// [`cargo:rerun-if-changed=PATH`](https://doc.rust-lang.org/cargo/reference/build-scripts.html#rerun-if-changed)
/// instructions for Cargo.
///
/// If set, writes instructions to `stdout` for Cargo so that it understands
/// when to rerun the build script. By default, this setting is enabled if
/// the `CARGO` environment variable is set. The `CARGO` environment
/// variable is set by Cargo for build scripts. Therefore, this setting
/// should be enabled automatically when run from a build script. However,
/// the method of detection is not completely reliable since the `CARGO`
/// environment variable can have been set by anything else. If writing the
/// instructions to `stdout` is undesireable, you can disable this setting
/// explicitly.
pub fn emit_rerun_if_changed(mut self, enable: bool) -> Self {
self.emit_rerun_if_changed = enable;
self
}

/// Compile the .proto files and execute code generation.
pub fn compile(
self,
Expand Down Expand Up @@ -415,6 +435,19 @@ impl Builder {
config.protoc_arg(arg);
}

if self.emit_rerun_if_changed {
for path in protos.iter() {
println!("cargo:rerun-if-changed={}", path.as_ref().display())
}

for path in includes.iter() {
// Cargo will watch the **entire** directory recursively. If we
// could figure out which files are imported by our protos we
// could specify only those files instead.
println!("cargo:rerun-if-changed={}", path.as_ref().display())
}
}

config.service_generator(self.service_generator());

config.compile_protos(protos, includes)?;
Expand Down