fix(plan): stdout logic for valid output files (#1249)

* feat: cleanup build plan logic and stdout

Don't let build plans generate anything other than the build plan
itself. If an error or warning should be generated, it should be
outputted to stderr. That way consumers can be pretty confident that the
output is only ever in valid TOML/JSON format.

* docs: add expected output behavior of -- plan

* chore: fix linting error

---------

Co-authored-by: Jake Runzer <jakerunzer@gmail.com>

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])