feat: Export conda explicit specification file from project

docs/reference/cli.md

@@ -1178,6 +1178,33 @@ List the environments in the manifest file.
 pixi project environment list
 ```
 
+### `project export conda_explicit_spec`
+
+Render a platform-specific conda [explicit specification file](https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html#building-identical-conda-environments)
+for an environment. The file can be then used to create a conda environment using conda/mamba:
+
+```shell
+mamba create --name <env> --file <explicit spec file>
+```
+
+As the explicit specification file format does not support pypi-dependencies, use the `--ignore-pypi-errors` option to ignore those dependencies.
+
+##### Arguments
+
+1. `<OUTPUT_DIR>`:  Output directory for rendered explicit environment spec files.
+
+##### Options
+
+- `--environment <ENVIRONMENT> (-e)`: Environment to render. Can be repeated for multiple envs. Defaults to all environments.
+- `--platform <PLATFORM> (-p)`: The platform to render. Can be repeated for multiple platforms. Defaults to all platforms available for selected environments.
+- `--ignore-pypi-errors`: PyPI dependencies are not supported in the conda explicit spec file. This flag allows creating the spec file even if PyPI dependencies are present.
+
+```sh
+pixi project export conda_explicit_spec output
+pixi project export conda_explicit_spec -e default -e test -p linux-64 output
+```
+
+
 ### `project platform add`
 
 Adds a platform(s) to the manifest file and updates the lock file.

src/cli/project/export/conda_explicit_spec.rs

@@ -0,0 +1,236 @@
+use std::collections::HashSet;
+use std::fs;
+use std::path::{Path, PathBuf};
+
+use clap::Parser;
+use miette::{Context, IntoDiagnostic};
+
+use crate::cli::cli_config::PrefixUpdateConfig;
+use crate::cli::LockFileUsageArgs;
+use crate::lock_file::UpdateLockFileOptions;
+use crate::Project;
+use rattler_conda_types::{ExplicitEnvironmentEntry, ExplicitEnvironmentSpec, Platform};
+use rattler_lock::{CondaPackage, Environment, Package};
+
+#[derive(Debug, Parser)]
+#[clap(arg_required_else_help = false)]
+pub struct Args {
+    /// Output directory for rendered explicit environment spec files
+    pub output_dir: PathBuf,
+
+    /// Environment to render. Can be repeated for multiple envs. Defaults to all environments
+    #[arg(short, long)]
+    pub environment: Option<Vec<String>>,
+
+    /// The platform to render. Can be repeated for multiple platforms.
+    /// Defaults to all platforms available for selected environments.
+    #[arg(short, long)]
+    pub platform: Option<Vec<Platform>>,
+
+    /// PyPI dependencies are not supported in the conda explicit spec file.
+    /// This flag allows creating the spec file even if PyPI dependencies are present.
+    #[arg(long, default_value = "false")]
+    pub ignore_pypi_errors: bool,
+
+    #[clap(flatten)]
+    pub lock_file_usage: LockFileUsageArgs,
+
+    #[clap(flatten)]
+    pub prefix_update_config: PrefixUpdateConfig,
+}
+
+fn build_explicit_spec<'a>(
+    platform: &Platform,
+    conda_packages: impl IntoIterator<Item = &'a CondaPackage>,
+) -> miette::Result<ExplicitEnvironmentSpec> {
+    let mut packages = Vec::new();
+
+    for cp in conda_packages {
+        let prec = cp.package_record();
+        let mut url = cp.url().to_owned();
+        let hash = prec.md5.ok_or(miette::miette!(
+            "Package {} does not contain an md5 hash",
+            prec.name.as_normalized()
+        ))?;
+
+        url.set_fragment(Some(&format!("{:x}", hash)));
+
+        packages.push(ExplicitEnvironmentEntry {
+            url: url.to_owned(),
+        });
+    }
+
+    Ok(ExplicitEnvironmentSpec {
+        platform: Some(*platform),
+        packages,
+    })
+}
+
+fn render_explicit_spec(
+    target: impl AsRef<Path>,
+    exp_env_spec: &ExplicitEnvironmentSpec,
+) -> miette::Result<()> {
+    if exp_env_spec.packages.is_empty() {
+        return Ok(());
+    }
+
+    let target = target.as_ref();
+
+    let mut environment = String::new();
+    environment.push_str("# Generated by `pixi project export`\n");
+    environment.push_str(exp_env_spec.to_spec_string().as_str());
+
+    fs::write(target, environment)
+        .into_diagnostic()
+        .with_context(|| format!("failed to write environment file: {}", target.display()))?;
+
+    Ok(())
+}
+
+fn render_env_platform(
+    output_dir: &Path,
+    env_name: &str,
+    env: &Environment,
+    platform: &Platform,
+    ignore_pypi_errors: bool,
+) -> miette::Result<()> {
+    let packages = env.packages(*platform).ok_or(miette::miette!(
+        "platform '{platform}' not found for env {}",
+        env_name,
+    ))?;
+
+    let mut conda_packages_from_lockfile: Vec<CondaPackage> = Vec::new();
+
+    for package in packages {
+        match package {
+            Package::Conda(p) => conda_packages_from_lockfile.push(p),
+            Package::Pypi(pyp) => {
+                if ignore_pypi_errors {
+                    tracing::warn!(
+                        "ignoring PyPI package {} since PyPI packages are not supported",
+                        pyp.data().package.name
+                    );
+                } else {
+                    miette::bail!(
+                        "PyPI packages are not supported. Specify `--ignore-pypi-errors` to ignore this error \
+                        or `--write-pypi-requirements` to write pypi requirements to a separate requirements.txt file"
+                    );
+                }
+            }
+        }
+    }
+
+    let ees = build_explicit_spec(platform, &conda_packages_from_lockfile)?;
+
+    tracing::info!("Creating conda explicit spec for env: {env_name} platform: {platform}");
+    let target = output_dir
+        .join(format!("{}_{}_conda_spec.txt", env_name, platform))
+        .into_os_string();
+
+    render_explicit_spec(target, &ees)?;
+
+    Ok(())
+}
+
+pub async fn execute(project: Project, args: Args) -> miette::Result<()> {
+    let lockfile = project
+        .update_lock_file(UpdateLockFileOptions {
+            lock_file_usage: args.prefix_update_config.lock_file_usage(),
+            no_install: args.prefix_update_config.no_install,
+            ..UpdateLockFileOptions::default()
+        })
+        .await?
+        .lock_file;
+
+    let mut environments = Vec::new();
+    if let Some(env_names) = args.environment {
+        for env_name in &env_names {
+            environments.push((
+                env_name.to_string(),
+                lockfile
+                    .environment(env_name)
+                    .ok_or(miette::miette!("unknown environment {}", env_name))?,
+            ));
+        }
+    } else {
+        for (env_name, env) in lockfile.environments() {
+            environments.push((env_name.to_string(), env));
+        }
+    };
+
+    let mut env_platform = Vec::new();
+
+    for (env_name, env) in environments {
+        let available_platforms: HashSet<Platform> = HashSet::from_iter(env.platforms());
+
+        if let Some(ref platforms) = args.platform {
+            for plat in platforms {
+                if available_platforms.contains(plat) {
+                    env_platform.push((env_name.clone(), env.clone(), *plat));
+                } else {
+                    tracing::warn!(
+                        "Platform {} not available for environment {}. Skipping...",
+                        plat,
+                        env_name,
+                    );
+                }
+            }
+        } else {
+            for plat in available_platforms {
+                env_platform.push((env_name.clone(), env.clone(), plat));
+            }
+        }
+    }
+
+    fs::create_dir_all(&args.output_dir).ok();
+
+    for (env_name, env, plat) in env_platform {
+        render_env_platform(
+            &args.output_dir,
+            &env_name,
+            &env,
+            &plat,
+            args.ignore_pypi_errors,
+        )?;
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+
+    use super::*;
+    use rattler_lock::LockFile;
+    use tempfile::tempdir;
+
+    #[test]
+    fn test_render_conda_explicit_spec() {
+        let path = Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("src/cli/project/export/test-data/testenv/pixi.lock");
+        let lockfile = LockFile::from_path(&path).unwrap();
+
+        let output_dir = tempdir().unwrap();
+
+        for (env_name, env) in lockfile.environments() {
+            for platform in env.platforms() {
+                // example contains pypi dependencies so should fail if `ignore_pypi_errors` is
+                // false.
+                assert!(
+                    render_env_platform(output_dir.path(), env_name, &env, &platform, false)
+                        .is_err()
+                );
+                render_env_platform(output_dir.path(), env_name, &env, &platform, true).unwrap();
+
+                let file_path = output_dir
+                    .path()
+                    .join(format!("{}_{}_conda_spec.txt", env_name, platform));
+                insta::assert_snapshot!(
+                    format!("test_render_conda_explicit_spec_{}_{}", env_name, platform),
+                    fs::read_to_string(file_path).unwrap()
+                );
+            }
+        }
+    }
+}

src/cli/project/export/mod.rs

@@ -0,0 +1,31 @@
+use std::path::PathBuf;
+pub mod conda_explicit_spec;
+
+use crate::Project;
+use clap::Parser;
+
+/// Commands to export projects to other formats
+#[derive(Parser, Debug)]
+pub struct Args {
+    /// The path to 'pixi.toml' or 'pyproject.toml'
+    #[clap(long, global = true)]
+    pub manifest_path: Option<PathBuf>,
+
+    #[clap(subcommand)]
+    pub command: Command,
+}
+
+#[derive(Parser, Debug)]
+pub enum Command {
+    /// Export project environment to a conda explicit specification file
+    #[clap(visible_alias = "ces")]
+    CondaExplicitSpec(conda_explicit_spec::Args),
+}
+
+pub async fn execute(args: Args) -> miette::Result<()> {
+    let project = Project::load_or_else_discover(args.manifest_path.as_deref())?;
+    match args.command {
+        Command::CondaExplicitSpec(args) => conda_explicit_spec::execute(project, args).await?,
+    };
+    Ok(())
+}

src/cli/project/export/snapshots/pixi__cli__project__export__conda_explicit_spec__tests__test_render_conda_explicit_spec_default_linux-64.snap

@@ -0,0 +1,46 @@
+---
+source: src/cli/project/export/conda_explicit_spec.rs
+expression: "fs::read_to_string(file_path).unwrap()"
+---
+# Generated by `pixi project export`
+# platform: linux-64
+@EXPLICIT
+https://conda.anaconda.org/conda-forge/linux-64/_libgcc_mutex-0.1-conda_forge.tar.bz2#d7c89558ba9fa0495403155b64376d81
+https://conda.anaconda.org/conda-forge/linux-64/_openmp_mutex-4.5-2_gnu.tar.bz2#73aaf86a425cc6e73fcf236a5a46396d
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src/cli/project/export/snapshots/pixi__cli__project__export__conda_explicit_spec__tests__test_render_conda_explicit_spec_default_osx-64.snap

@@ -0,0 +1,23 @@
+---
+source: src/cli/project/export/conda_explicit_spec.rs
+expression: "fs::read_to_string(file_path).unwrap()"
+---
+# Generated by `pixi project export`
+# platform: osx-64
+@EXPLICIT
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