From 4a2471c22dfd46d7d42bf65d000cdcca08926c47 Mon Sep 17 00:00:00 2001
From: Jason Hall <jason@chainguard.dev>
Date: Wed, 15 Oct 2025 18:06:54 -0400
Subject: [PATCH] support building --example and --bin

Signed-off-by: Jason Hall <jason@chainguard.dev>
---
 README.md                        | 12 ++++++++++++
 src/builder/mod.rs               | 32 ++++++++++++++++++++++++++++----
 tests/testdata/build_example.txt | 26 ++++++++++++++++++++++++++
 3 files changed, 66 insertions(+), 4 deletions(-)
 create mode 100644 tests/testdata/build_example.txt

diff --git a/README.md b/README.md
index 6a2fd17..aac3171 100644
--- a/README.md
+++ b/README.md
@@ -135,9 +135,21 @@ krust build
 ### Build with custom cargo arguments
 
 ```bash
+# Build with features
 krust build -- --features=prod
+
+# Build an example binary
+krust build -- --example http_server
+
+# Build a specific binary target
+krust build -- --bin my-app
+
+# Combine multiple flags
+krust build -- --example server --features=tls
 ```
 
+When building examples or specific binaries, krust automatically detects the correct binary name and path from the cargo arguments.
+
 ## Supported Platforms
 
 - `linux/amd64` (x86_64-unknown-linux-musl)
diff --git a/src/builder/mod.rs b/src/builder/mod.rs
index a7c097c..5297e22 100644
--- a/src/builder/mod.rs
+++ b/src/builder/mod.rs
@@ -142,10 +142,12 @@ impl RustBuilder {
         }
 
         let binary_name = self.get_binary_name()?;
-        let binary_path = target_dir
-            .join(&self.target)
-            .join("release")
-            .join(&binary_name);
+        let binary_subdir = self.get_binary_subdir();
+        let mut binary_path = target_dir.join(&self.target).join("release");
+        if let Some(subdir) = binary_subdir {
+            binary_path = binary_path.join(subdir);
+        }
+        binary_path = binary_path.join(&binary_name);
 
         // Sometimes cargo build completes but the binary isn't immediately visible
         // due to filesystem sync issues. Give it a moment.
@@ -169,6 +171,18 @@ impl RustBuilder {
     }
 
     fn get_binary_name(&self) -> Result<String> {
+        // Check if --example or --bin was specified
+        let mut i = 0;
+        while i < self.cargo_args.len() {
+            if (self.cargo_args[i] == "--example" || self.cargo_args[i] == "--bin")
+                && i + 1 < self.cargo_args.len()
+            {
+                return Ok(self.cargo_args[i + 1].clone());
+            }
+            i += 1;
+        }
+
+        // Fall back to package name
         let cargo_toml_path = self.project_path.join("Cargo.toml");
         let content =
             std::fs::read_to_string(&cargo_toml_path).context("Failed to read Cargo.toml")?;
@@ -184,6 +198,16 @@ impl RustBuilder {
 
         Ok(name.to_string())
     }
+
+    fn get_binary_subdir(&self) -> Option<&str> {
+        // Check if --example was specified (examples go in "examples/" subdir)
+        for (i, arg) in self.cargo_args.iter().enumerate() {
+            if arg == "--example" && i + 1 < self.cargo_args.len() {
+                return Some("examples");
+            }
+        }
+        None
+    }
 }
 
 pub fn get_rust_target_triple(platform: &str) -> Result<String> {
diff --git a/tests/testdata/build_example.txt b/tests/testdata/build_example.txt
new file mode 100644
index 0000000..8c0179e
--- /dev/null
+++ b/tests/testdata/build_example.txt
@@ -0,0 +1,26 @@
+# Test building examples with --example flag
+
+-- Cargo.toml --
+[package]
+name = "test-app"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+-- src/main.rs --
+fn main() {
+    println!("Hello from main!");
+}
+
+-- examples/example_server.rs --
+fn main() {
+    println!("Hello from example!");
+}
+
+# Build the example binary
+[linux] env KRUST_REPO=ttl.sh/test exec ./krust build --no-push --platform linux/amd64 . -- --example example_server
+[darwin] env KRUST_REPO=ttl.sh/test exec ./krust build --no-push --platform linux/amd64 . -- --example example_server
+stderr 'Building Rust project'
+stderr 'Successfully built binary'
+stderr 'examples/example_server'
+stderr 'Successfully built image'