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add a function to populate flags from an arbitrary environment variab…
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…le (#818)
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@nagisa
nagisa authored Jul 17, 2023
1 parent 17c8858 commit d2a6839
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Showing 2 changed files with 83 additions and 41 deletions.
12 changes: 10 additions & 2 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,17 @@ number of different environment variables.
certain `TARGET`s, it also is assumed to know about other flags (most
common is `-fPIC`).
* `AR` - the `ar` (archiver) executable to use to build the static library.
* `CRATE_CC_NO_DEFAULTS` - the default compiler flags may cause conflicts in some cross compiling scenarios. Setting this variable will disable the generation of default compiler flags.
* `CRATE_CC_NO_DEFAULTS` - the default compiler flags may cause conflicts in
some cross compiling scenarios. Setting this variable
will disable the generation of default compiler
flags.
* `CXX...` - see [C++ Support](#c-support).

Furthermore, projects using this crate may specify custom environment variables
to be inspected, for example via the `Build::try_flags_from_environment`
function. Consult the project’s own documentation or its use of the `cc` crate
for any additional variables it may use.

Each of these variables can also be supplied with certain prefixes and suffixes,
in the following prioritized order:

Expand All @@ -94,7 +102,7 @@ in the following prioritized order:
3. `<build-kind>_<var>` - for example, `HOST_CC` or `TARGET_CFLAGS`
4. `<var>` - a plain `CC`, `AR` as above.

If none of these variables exist, cc-rs uses built-in defaults
If none of these variables exist, cc-rs uses built-in defaults.

In addition to the above optional environment variables, `cc-rs` has some
functions with hard requirements on some variables supplied by [cargo's
Expand Down
112 changes: 73 additions & 39 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -563,6 +563,35 @@ impl Build {
self
}

/// Add flags from the specified environment variable.
///
/// Normally the `cc` crate will consult with the standard set of environment
/// variables (such as `CFLAGS` and `CXXFLAGS`) to construct the compiler invocation. Use of
/// this method provides additional levers for the end user to use when configuring the build
/// process.
///
/// Just like the standard variables, this method will search for an environment variable with
/// appropriate target prefixes, when appropriate.
///
/// # Examples
///
/// This method is particularly beneficial in introducing the ability to specify crate-specific
/// flags.
///
/// ```no_run
/// cc::Build::new()
/// .file("src/foo.c")
/// .try_flags_from_environment(concat!(env!("CARGO_PKG_NAME"), "_CFLAGS"))
/// .expect("the environment variable must be specified and UTF-8")
/// .compile("foo");
/// ```
///
pub fn try_flags_from_environment(&mut self, environ_key: &str) -> Result<&mut Build, Error> {
let flags = self.envflags(environ_key)?;
self.flags.extend(flags.into_iter().map(Into::into));
Ok(self)
}

/// Set the `-shared` flag.
///
/// When enabled, the compiler will produce a shared object which can
Expand Down Expand Up @@ -1471,7 +1500,6 @@ impl Build {
let target = self.get_target()?;

let mut cmd = self.get_base_compiler()?;
let envflags = self.envflags(if self.cpp { "CXXFLAGS" } else { "CFLAGS" });

// Disable default flag generation via `no_default_flags` or environment variable
let no_defaults = self.no_default_flags || self.getenv("CRATE_CC_NO_DEFAULTS").is_some();
Expand All @@ -1482,8 +1510,10 @@ impl Build {
println!("Info: default compiler flags are disabled");
}

for arg in envflags {
cmd.push_cc_arg(arg.into());
if let Ok(flags) = self.envflags(if self.cpp { "CXXFLAGS" } else { "CFLAGS" }) {
for arg in flags {
cmd.push_cc_arg(arg.into());
}
}

for directory in self.include_directories.iter() {
Expand Down Expand Up @@ -1990,7 +2020,7 @@ impl Build {

fn has_flags(&self) -> bool {
let flags_env_var_name = if self.cpp { "CXXFLAGS" } else { "CFLAGS" };
let flags_env_var_value = self.get_var(flags_env_var_name);
let flags_env_var_value = self.getenv_with_target_prefixes(flags_env_var_name);
if let Ok(_) = flags_env_var_value {
true
} else {
Expand Down Expand Up @@ -2437,7 +2467,7 @@ impl Build {
tool.args.is_empty(),
"CUDA compilation currently assumes empty pre-existing args"
);
let nvcc = match self.get_var("NVCC") {
let nvcc = match self.getenv_with_target_prefixes("NVCC") {
Err(_) => "nvcc".into(),
Ok(nvcc) => nvcc,
};
Expand Down Expand Up @@ -2509,34 +2539,6 @@ impl Build {
Ok(tool)
}

fn get_var(&self, var_base: &str) -> Result<String, Error> {
let target = self.get_target()?;
let host = self.get_host()?;
let kind = if host == target { "HOST" } else { "TARGET" };
let target_u = target.replace("-", "_");
let res = self
.getenv(&format!("{}_{}", var_base, target))
.or_else(|| self.getenv(&format!("{}_{}", var_base, target_u)))
.or_else(|| self.getenv(&format!("{}_{}", kind, var_base)))
.or_else(|| self.getenv(var_base));

match res {
Some(res) => Ok(res),
None => Err(Error::new(
ErrorKind::EnvVarNotFound,
&format!("Could not find environment variable {}.", var_base),
)),
}
}

fn envflags(&self, name: &str) -> Vec<String> {
self.get_var(name)
.unwrap_or(String::new())
.split_ascii_whitespace()
.map(|slice| slice.to_string())
.collect()
}

/// Returns a fallback `cc_compiler_wrapper` by introspecting `RUSTC_WRAPPER`
fn rustc_wrapper_fallback() -> Option<String> {
// No explicit CC wrapper was detected, but check if RUSTC_WRAPPER
Expand All @@ -2557,7 +2559,7 @@ impl Build {

/// Returns compiler path, optional modifier name from whitelist, and arguments vec
fn env_tool(&self, name: &str) -> Option<(String, Option<String>, Vec<String>)> {
let tool = match self.get_var(name) {
let tool = match self.getenv_with_target_prefixes(name) {
Ok(tool) => tool,
Err(_) => return None,
};
Expand Down Expand Up @@ -2628,7 +2630,7 @@ impl Build {
match &self.cpp_link_stdlib {
Some(s) => Ok(s.as_ref().map(|s| (*s).to_string())),
None => {
if let Ok(stdlib) = self.get_var("CXXSTDLIB") {
if let Ok(stdlib) = self.getenv_with_target_prefixes("CXXSTDLIB") {
if stdlib.is_empty() {
Ok(None)
} else {
Expand Down Expand Up @@ -2691,9 +2693,11 @@ impl Build {

fn try_get_archiver_and_flags(&self) -> Result<(Command, String, bool), Error> {
let (mut cmd, name) = self.get_base_archiver()?;
let flags = self.envflags("ARFLAGS");
let mut any_flags = !flags.is_empty();
cmd.args(flags);
let mut any_flags = false;
if let Ok(flags) = self.envflags("ARFLAGS") {
any_flags = any_flags | !flags.is_empty();
cmd.args(flags);
}
for flag in &self.ar_flags {
any_flags = true;
cmd.arg(&**flag);
Expand Down Expand Up @@ -2736,7 +2740,9 @@ impl Build {
/// see [`get_ranlib()`] for the complete description.
pub fn try_get_ranlib(&self) -> Result<Command, Error> {
let mut cmd = self.get_base_ranlib()?;
cmd.args(self.envflags("RANLIBFLAGS"));
if let Ok(flags) = self.envflags("RANLIBFLAGS") {
cmd.args(flags);
}
Ok(cmd)
}

Expand Down Expand Up @@ -3133,6 +3139,34 @@ impl Build {
}
}

fn getenv_with_target_prefixes(&self, var_base: &str) -> Result<String, Error> {
let target = self.get_target()?;
let host = self.get_host()?;
let kind = if host == target { "HOST" } else { "TARGET" };
let target_u = target.replace("-", "_");
let res = self
.getenv(&format!("{}_{}", var_base, target))
.or_else(|| self.getenv(&format!("{}_{}", var_base, target_u)))
.or_else(|| self.getenv(&format!("{}_{}", kind, var_base)))
.or_else(|| self.getenv(var_base));

match res {
Some(res) => Ok(res),
None => Err(Error::new(
ErrorKind::EnvVarNotFound,
&format!("Could not find environment variable {}.", var_base),
)),
}
}

fn envflags(&self, name: &str) -> Result<Vec<String>, Error> {
Ok(self
.getenv_with_target_prefixes(name)?
.split_ascii_whitespace()
.map(|slice| slice.to_string())
.collect())
}

fn print(&self, s: &str) {
if self.cargo_metadata {
println!("{}", s);
Expand Down

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