Add --env for benchmark environment overrides

src/benchmark/benchmark_result.rs

@@ -18,15 +18,13 @@ pub struct BenchmarkResult {
     /// regardless of any custom name.
     pub command: String,
 
-    /// The custom name after parameter substitution, if it differs from `command`.
-    /// For example, `--command-name="wait {duration}s"` with `duration=1`
-    /// produces `Some("wait 1s")`. Without a custom name, or when the expanded
-    /// name equals `command`, this is `None`.
+    /// The custom or automatically generated name after parameter substitution,
+    /// if it differs from `command`. Automatic names include environment overrides.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub name: Option<String>,
 
-    /// The custom name (or `command`), followed by parameters not used in the
-    /// command template, in command-line order. For example, `sleep {duration}`
+    /// The name, followed by parameters not used in the command or environment
+    /// templates, in command-line order. For example, `sleep {duration}`
     /// with `duration=1`, `branch=main`, and the custom name `wait {duration}s`
     /// produces `wait 1s (branch = main)`. Without the custom name, this is
     /// `sleep 1 (branch = main)`. Used in summaries and table exports.
@@ -40,6 +38,10 @@ pub struct BenchmarkResult {
     /// Parameter values for this benchmark
     #[serde(skip_serializing_if = "BTreeMap::is_empty")]
     pub parameters: BTreeMap<String, Parameter>,
+
+    /// Explicit environment overrides after parameter substitution.
+    #[serde(skip_serializing_if = "BTreeMap::is_empty")]
+    pub environment: BTreeMap<String, String>,
 }
 
 impl BenchmarkResult {

src/benchmark/executor.rs

@@ -215,6 +215,7 @@ impl Executor for ShellExecutor<'_> {
     ) -> Result<Measurement> {
         let on_windows_cmd = cfg!(windows) && *self.shell == Shell::Default("cmd.exe");
         let mut command_builder = self.shell.command();
+        command_builder.envs(command.get_environment());
         command_builder.arg(if on_windows_cmd { "/C" } else { "-c" });
 
         // Windows needs special treatment for its behavior on parsing cmd arguments

src/benchmark/mod.rs

@@ -61,8 +61,9 @@ impl<'a> Benchmark<'a> {
         output_policy: &CommandOutputPolicy,
         iteration: executor::BenchmarkIteration,
     ) -> Result<Measurement> {
+        let command = command.clone().with_environment_from(self.command);
         self.executor
-            .run_intermediate_command_and_measure(command, iteration, output_policy)
+            .run_intermediate_command_and_measure(&command, iteration, output_policy)
             .map_err(|error| {
                 let hint = if cfg!(windows) {
                     "Append ' || exit /b 0' to the command if this failure can be ignored."
@@ -443,6 +444,11 @@ impl<'a> Benchmark<'a> {
         Ok(BenchmarkResult {
             command,
             name,
+            environment: self
+                .command
+                .get_environment()
+                .map(|(name, value)| (name.to_owned(), value))
+                .collect(),
             display_name: self.command.get_name_with_unused_parameters(),
             measurements,
             parameters: self