cli: add show-env subcommand

README.md

@@ -298,6 +298,17 @@ cargo llvm-cov --no-report --features b
 cargo llvm-cov --no-run --lcov
 ```
 
+In combination with the `show-env` subcommand, coverage can also be produced from arbitrary binaries:
+
+```sh
+cargo llvm-cov clean --workspace # remove artifacts that may affect the coverage results
+source <(cargo llvm-cov show-env --export-prefix)
+cargo build # build rust binaries
+# commands using binaries in target/debug/*, including `cargo test`
+# ...
+cargo llvm-cov --no-run --lcov # generate report without tests
+```
+
 To exclude specific file patterns from the report, use the `--ignore-filename-regex` option.
 
 ```sh

src/cli.rs

@@ -177,6 +177,14 @@ pub(crate) enum Subcommand {
     )]
     Run(Box<RunOptions>),
 
+    /// Output the environment set by cargo-llvm-cov to build Rust projects.
+    #[clap(
+        bin_name = "cargo llvm-cov show-env",
+        max_term_width = MAX_TERM_WIDTH,
+        setting = AppSettings::DeriveDisplayOrder,
+    )]
+    ShowEnv(ShowEnvOptions),
+
     /// Remove artifacts that cargo-llvm-cov has generated in the past
     #[clap(
         bin_name = "cargo llvm-cov clean",
@@ -430,6 +438,13 @@ impl RunOptions {
     }
 }
 
+#[derive(Debug, Parser)]
+pub(crate) struct ShowEnvOptions {
+    /// Prepend "export " to each line, so that the output is suitable to be sourced by bash.
+    #[clap(long)]
+    pub(crate) export_prefix: bool,
+}
+
 #[derive(Debug, Parser)]
 pub(crate) struct CleanOptions {
     /// Remove artifacts that may affect the coverage results of packages in the workspace.

src/main.rs

@@ -37,7 +37,7 @@ use std::{
 use anyhow::{Context as _, Result};
 use camino::{Utf8Path, Utf8PathBuf};
 use clap::Parser;
-use cli::RunOptions;
+use cli::{RunOptions, ShowEnvOptions};
 use regex::Regex;
 use walkdir::WalkDir;
 
@@ -57,6 +57,7 @@ fn main() {
 
 fn try_main() -> Result<()> {
     let Opts::LlvmCov(mut args) = Opts::parse();
+    let cx = &context_from_args(&mut args)?;
 
     match args.subcommand {
         Some(Subcommand::Demangle) => {
@@ -92,6 +93,10 @@ fn try_main() -> Result<()> {
             }
         }
 
+        Some(Subcommand::ShowEnv(options)) => {
+            set_env(cx, &mut ShowEnvWriter { target: std::io::stdout(), options });
+        }
+
         None => {
             term::set_quiet(args.quiet);
             if args.doctests {
@@ -102,18 +107,6 @@ fn try_main() -> Result<()> {
                 warn!("--doc option is unstable");
             }
 
-            let cx = &Context::new(
-                args.build(),
-                args.manifest(),
-                args.cov(),
-                args.workspace,
-                &args.exclude,
-                &args.package,
-                args.quiet,
-                args.doctests,
-                args.no_run,
-            )?;
-
             clean::clean_partial(cx)?;
             create_dirs(cx)?;
             match (args.no_run, cx.cov.no_report) {
@@ -134,6 +127,20 @@ fn try_main() -> Result<()> {
     Ok(())
 }
 
+fn context_from_args(args: &mut Args) -> Result<Context> {
+    Context::new(
+        args.build(),
+        args.manifest(),
+        args.cov(),
+        args.workspace,
+        &args.exclude,
+        &args.package,
+        args.quiet,
+        args.doctests,
+        args.no_run,
+    )
+}
+
 fn create_dirs(cx: &Context) -> Result<()> {
     fs::create_dir_all(&cx.ws.target_dir)?;
 
@@ -153,7 +160,35 @@ fn create_dirs(cx: &Context) -> Result<()> {
     Ok(())
 }
 
-fn set_env(cx: &Context, cmd: &mut ProcessBuilder) {
+trait EnvTarget {
+    fn set(&mut self, key: &str, value: &str);
+}
+
+impl EnvTarget for ProcessBuilder {
+    fn set(&mut self, key: &str, value: &str) {
+        self.env(key, value);
+    }
+}
+
+struct ShowEnvWriter<W: std::io::Write> {
+    target: W,
+    options: ShowEnvOptions,
+}
+
+impl<W: std::io::Write> EnvTarget for ShowEnvWriter<W> {
+    fn set(&mut self, key: &str, value: &str) {
+        writeln!(
+            self.target,
+            r#"{prefix}{key}="{value}""#,
+            prefix = if self.options.export_prefix { "export " } else { "" },
+            key = key,
+            value = value,
+        )
+        .expect("failed to write to stdout");
+    }
+}
+
+fn set_env(cx: &Context, target: &mut impl EnvTarget) {
     let llvm_profile_file = cx.ws.target_dir.join(format!("{}-%m.profraw", cx.ws.package_name));
 
     let rustflags = &mut cx.ws.config.rustflags().unwrap_or_default();
@@ -192,12 +227,12 @@ fn set_env(cx: &Context, cmd: &mut ProcessBuilder) {
         }
     }
 
-    cmd.env("RUSTFLAGS", &rustflags);
+    target.set("RUSTFLAGS", rustflags);
     if let Some(rustdocflags) = rustdocflags {
-        cmd.env("RUSTDOCFLAGS", &rustdocflags);
+        target.set("RUSTDOCFLAGS", rustdocflags);
     }
-    cmd.env("LLVM_PROFILE_FILE", &*llvm_profile_file);
-    cmd.env("CARGO_INCREMENTAL", "0");
+    target.set("LLVM_PROFILE_FILE", llvm_profile_file.as_str());
+    target.set("CARGO_INCREMENTAL", "0");
 }
 
 fn run_test(cx: &Context, args: &Args) -> Result<()> {

tests/long-help.txt

@@ -196,6 +196,8 @@ OPTIONS:
 SUBCOMMANDS:
     run
             Run a binary or example and generate coverage report
+    show-env
+            Output the environment set by cargo-llvm-cov to build Rust projects
     clean
             Remove artifacts that cargo-llvm-cov has generated in the past
     help

tests/short-help.txt

@@ -147,6 +147,7 @@ OPTIONS:
             Print version information
 
 SUBCOMMANDS:
-    run      Run a binary or example and generate coverage report
-    clean    Remove artifacts that cargo-llvm-cov has generated in the past
-    help     Print this message or the help of the given subcommand(s)
+    run         Run a binary or example and generate coverage report
+    show-env    Output the environment set by cargo-llvm-cov to build Rust projects
+    clean       Remove artifacts that cargo-llvm-cov has generated in the past
+    help        Print this message or the help of the given subcommand(s)