fix(xtask): skip png conversion on legacy chafa

xtask/src/screenshots.rs

@@ -53,22 +53,42 @@ pub(crate) fn run(output: Option<PathBuf>, chafa: Option<PathBuf>, no_png: bool)
     }
 
     let png_requested = !no_png;
-    let mut chafa_binary: Option<PathBuf> = None;
-    if png_requested {
-        if let Some(ref path) = chafa {
+    let mut png_skip_reason: Option<String> = None;
+    let chafa_binary: Option<PathBuf> = if png_requested {
+        let candidate = if let Some(ref path) = chafa {
             if path.exists() {
-                chafa_binary = Some(path.clone());
+                Some(path.clone())
             } else {
                 bail!("specified chafa binary '{}' does not exist", path.display());
             }
-        } else if let Ok(found) = which("chafa") {
-            chafa_binary = Some(found);
         } else {
-            eprintln!(
-                "warning: chafa not found in PATH; skipping PNG conversion (install `chafa` or rerun with --no-png)"
-            );
+            which("chafa").ok()
+        };
+
+        if let Some(path) = candidate {
+            match chafa_supports_save(&path) {
+                Ok(true) => Some(path),
+                Ok(false) => {
+                    png_skip_reason = Some(format!(
+                        "chafa at '{}' lacks --save support; install chafa 1.14+ or rerun with --no-png",
+                        path.display()
+                    ));
+                    None
+                }
+                Err(err) => {
+                    eprintln!("warning: failed to probe chafa capabilities: {err}");
+                    png_skip_reason = Some("failed to verify chafa capabilities".to_string());
+                    None
                 }
             }
+        } else {
+            png_skip_reason =
+                Some("chafa not found in PATH; install it or rerun with --no-png".to_string());
+            None
+        }
+    } else {
+        None
+    };
 
     let runtime = Runtime::new().context("failed to create tokio runtime")?;
 
@@ -86,7 +106,7 @@ pub(crate) fn run(output: Option<PathBuf>, chafa: Option<PathBuf>, no_png: bool)
                 scene.height,
                 &output_dir,
                 scene.name,
-                Some(binary.as_path()),
+                binary.as_path(),
             )
         {
             eprintln!("warning: {}", err);
@@ -94,11 +114,13 @@ pub(crate) fn run(output: Option<PathBuf>, chafa: Option<PathBuf>, no_png: bool)
     }
 
     println!("Screenshots written to {}", output_dir.display());
-    if png_requested {
-        if chafa_binary.is_none() {
-            println!("PNG conversion skipped (install `chafa` or pass --no-png to disable)");
-        }
+    if png_requested && chafa_binary.is_none() {
+        if let Some(reason) = png_skip_reason {
+            println!("PNG conversion skipped ({reason})");
         } else {
+            println!("PNG conversion skipped");
+        }
+    } else if !png_requested {
         println!("PNG conversion skipped (use --no-png=false or omit flag to enable)");
     }
 
@@ -111,14 +133,10 @@ fn convert_to_png(
     height: u16,
     output_dir: &Path,
     name: &str,
-    chafa_path: Option<&Path>,
+    chafa_path: &Path,
 ) -> Result<()> {
     let png_path = output_dir.join(format!("{}.png", name));
-    let mut command = if let Some(path) = chafa_path {
-        Command::new(path)
-    } else {
-        Command::new("chafa")
-    };
+    let mut command = Command::new(chafa_path);
     let status = command
         .arg("--size")
         .arg(format!("{}x{}", width, height))
@@ -137,6 +155,20 @@ fn convert_to_png(
     Ok(())
 }
 
+fn chafa_supports_save(chafa_path: &Path) -> Result<bool> {
+    let output = Command::new(chafa_path)
+        .arg("--help")
+        .output()
+        .with_context(|| {
+            format!(
+                "failed to run '{}' to probe capabilities",
+                chafa_path.display()
+            )
+        })?;
+    let help = String::from_utf8_lossy(&output.stdout);
+    Ok(help.contains("--save"))
+}
+
 fn scenes() -> &'static [SceneSpec] {
     &[
         SceneSpec {