run and eval can write their JSON to a file (--json-out) (#1242)

apps/solidcraft-cli/src/main.rs

@@ -1,8 +1,8 @@
 //! SolidCraft headless command line.
 //!
 //! ```text
-//! solidcraft-cli run <script.json|design.solidcraft|part.step|mesh.3mf> [--in design|part.step|mesh.3mf] [--out FILE]... [--save FILE] [--quiet] [--allow-errors]
-//! solidcraft-cli eval <script.json|design.solidcraft|part.step> (alias: inspect) measurements as JSON
+//! solidcraft-cli run <script.json|design.solidcraft|part.step|mesh.3mf> [--in design|part.step|mesh.3mf] [--out FILE]... [--save FILE] [--quiet] [--results] [--json-out FILE] [--allow-errors]
+//! solidcraft-cli eval <script.json|design.solidcraft|part.step> [--json-out FILE] (alias: inspect) measurements as JSON
 //! solidcraft-cli script <design.solidcraft> [--out script.json]     the design's history as a command script
 //! solidcraft-cli bench-open <design.solidcraft | part.step> [--parse-only] loading timings as JSON lines
 //! solidcraft-cli bench-agent [--scale F] [--save F] [--script-out F] a ~1,300-body design built command by command, timed
@@ -37,10 +37,12 @@ use solidcraft_engine::Session;
 use solidcraft_engine::render::{StandardView, render_png};
 
 const USAGE: &str = "usage:
-  solidcraft-cli run <script.json|design.solidcraft|part.step> [--in design.solidcraft|part.step] [--out FILE]... [--save FILE] [--quiet] [--results] [--allow-errors]
+  solidcraft-cli run <script.json|design.solidcraft|part.step> [--in design.solidcraft|part.step] [--out FILE]... [--save FILE] [--quiet] [--results] [--json-out FILE] [--allow-errors]
   solidcraft-cli run --in <design.solidcraft|part.step> [--out FILE]...
       (a timeline feature that fails fails the run and nothing is written; --allow-errors writes anyway)
-  solidcraft-cli eval <script.json|design.solidcraft|part.step>     (alias: inspect; or --in FILE)
+  solidcraft-cli eval <script.json|design.solidcraft|part.step> [--json-out FILE]     (alias: inspect; or --in FILE)
+      (--json-out FILE writes the JSON that run (with --results, else the measurement) and eval print to FILE instead of stdout,
+       as plain UTF-8: a shell's > can re-encode it, e.g. Windows PowerShell adds a byte-order mark)
   solidcraft-cli script <design.solidcraft|script.json> [--out script.json]
       (the design's history as a command script that eval and run replay)
   solidcraft-cli bench-open <design.solidcraft | part.step> [--parse-only]
@@ -176,7 +178,36 @@ fn positional(args: &[String]) -> Option<&String> {
     None
 }
 
+/// `--json-out FILE`: where the JSON a command prints goes instead of stdout.
+fn json_out(args: &[String]) -> Result<Option<&str>, String> {
+    if !args.iter().any(|a| a == "--json-out") {
+        return Ok(None);
+    }
+    match flag(args, "--json-out") {
+        Some(file) if !file.starts_with("--") => Ok(Some(file)),
+        _ => Err("--json-out needs a FILE".to_string()),
+    }
+}
+
+/// `v` as indented JSON with a final newline: on stdout, or in `file`. The file is plain UTF-8
+/// with no byte-order mark, whatever the platform's shell does to redirected output (Windows
+/// PowerShell's `>` writes UTF-16, or UTF-8 with a BOM), so strict JSON readers take it.
+fn print_json(v: &Value, file: Option<&str>) -> Result<(), String> {
+    match file {
+        Some(file) => {
+            let mut text = pretty(v);
+            text.push('\n');
+            std::fs::write(file, text).map_err(|e| format!("{file}: {e}"))
+        }
+        None => {
+            println!("{}", pretty(v));
+            Ok(())
+        }
+    }
+}
+
 fn cmd_run(args: &[String]) -> Result<(), String> {
+    let json_out = json_out(args)?;
     let base = flag(args, "--in");
     let path = positional(args);
     if path.is_none() && base.is_none() {
@@ -216,10 +247,11 @@ fn cmd_run(args: &[String]) -> Result<(), String> {
         s.execute("file.save_as", &json!({"path": p})).map_err(|e| e.to_string())?;
     }
     if let Some(results) = results {
-        println!("{}", pretty(&results));
-    } else if !args.iter().any(|a| a == "--quiet") {
+        print_json(&results, json_out)?;
+    } else if json_out.is_some() || !args.iter().any(|a| a == "--quiet") {
+        // `--quiet` silences stdout; a file that was asked for is still written.
         let m = s.execute("inspect.measure", &json!({})).map_err(|e| e.to_string())?;
-        println!("{}", pretty(&m));
+        print_json(&m, json_out)?;
     }
     Ok(())
 }
@@ -238,6 +270,7 @@ fn timeline_ok(s: &Session) -> Result<(), String> {
 }
 
 fn cmd_eval(args: &[String]) -> Result<(), String> {
+    let json_out = json_out(args)?;
     let path = flag(args, "--in").or_else(|| positional(args).map(String::as_str)).ok_or_else(|| USAGE.to_string())?;
     let mut s = load(path)?;
     let m = s.execute("inspect.measure", &json!({})).map_err(|e| e.to_string())?;
@@ -250,8 +283,7 @@ fn cmd_eval(args: &[String]) -> Result<(), String> {
         "params": d["params"],
         "sketches": d["sketches"],
     });
-    println!("{}", pretty(&out));
-    Ok(())
+    print_json(&out, json_out)
 }
 
 /// A design's history as a command script (`timeline.export_script`): printed, or written to