fix(plan): stdout logic for valid output files

docs/pages/docs/cli.md

@@ -68,6 +68,7 @@ nixpacks plan examples/node
 ```
 
 By default, the plan is output in JSON format. You can output in TOML format with the `--format toml` option.
+The generated plan will be outputted to stdout, while some providers expose recoverable errors to stderr.
 
 View all plan options with
 

src/main.rs

@@ -76,7 +76,8 @@ struct Args {
 #[allow(clippy::large_enum_variant)]
 #[derive(Subcommand)]
 enum Commands {
-    /// Generate a build plan for an app
+    /// Generate a build plan for an app.
+    /// Generated plan will be outputted to stdout, while warnings might be outputted to stderr.
     Plan {
         /// App source
         path: String,

src/providers/node/mod.rs

@@ -631,7 +631,7 @@ fn version_number_to_pkg(version: u32) -> String {
 fn parse_node_version_into_pkg(node_version: &str) -> String {
     let default_node_pkg_name = version_number_to_pkg(DEFAULT_NODE_VERSION);
     let range: Range = node_version.parse().unwrap_or_else(|_| {
-        println!("Warning: node version {node_version} is not valid, using default node version {default_node_pkg_name}");
+        eprintln!("Warning: node version {node_version} is not valid, using default node version {default_node_pkg_name}");
         Range::parse(DEFAULT_NODE_VERSION.to_string()).unwrap()
     });
     let mut available_node_versions = AVAILABLE_NODE_VERSIONS.to_vec();

src/providers/node/turborepo.rs

@@ -97,7 +97,7 @@ impl Turborepo {
                     format!("{pkg_manager} --workspace {name} run start")
                 }));
             }
-            println!("Warning: Turborepo app `{name}` not found");
+            eprintln!("Warning: Turborepo app `{name}` not found");
         }
         if let Some(start_pipeline) = Turborepo::get_start_cmd(&turbo_cfg) {
             return Ok(Some(start_pipeline));

src/providers/php/mod.rs

@@ -209,13 +209,13 @@ impl PhpProvider {
             } else if v.contains("7.4") {
                 "7.4".to_string()
             } else {
-                println!(
+                eprintln!(
                     "Warning: PHP version {v} is not available, using PHP {DEFAULT_PHP_VERSION}"
                 );
                 DEFAULT_PHP_VERSION.to_string()
             }
         } else {
-            println!("Warning: No PHP version specified, using PHP {DEFAULT_PHP_VERSION}; see https://getcomposer.org/doc/04-schema.md#package-links for how to specify a PHP version.");
+            eprintln!("Warning: No PHP version specified, using PHP {DEFAULT_PHP_VERSION}; see https://getcomposer.org/doc/04-schema.md#package-links for how to specify a PHP version.");
             DEFAULT_PHP_VERSION.to_string()
         };
 

src/providers/python.rs

@@ -377,13 +377,10 @@ impl PythonProvider {
         Ok(asdf_versions.get("python").map(|s| {
             let parts: Vec<&str> = s.split('.').collect();
 
-            if parts.len() == 3 {
-                // this is the expected result, but will be unexpected to users
-                println!("Patch python version detected in .tool-versions, but not supported in nixpkgs.");
-            } else if parts.len() == 2 {
-                println!("Expected a python version string in the format x.y.z from .tool-versions");
-            } else {
-                println!("Could not find a python version string in the format x.y.z or x.y from .tool-versions");
+            // We expect there to be 3 or 2 parts (x.y.z) however, only x.y can be parsed.
+            // So we accept strip x.y.z -> x.y and warn that all other formats are invalid
+            if parts.len() != 3 && parts.len() != 2 {
+                eprintln!("Could not find a python version string in the format x.y.z or x.y from .tool-versions. Found {}. Skipping", parts.join("."));
             }
 
             format!("{}.{}", parts[0], parts[1])