Derive layout PCB path from .kicad_pro file (#525)

Previously, we tried to tolerative missing .kicad_pro file by also
looking for a unique .kicad_pcb file but this is unnecessary complexity.
We can safely assume a .kicad_pro file is present/necessary.

Author: akhilles

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to Semantic Versioning (https://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- Layout discovery now uses only `.kicad_pro` files, ignoring extra `.kicad_pcb` files in the layout directory.
+
 ## [0.3.38] - 2026-02-11
 
 ### Added

crates/pcb-layout/src/lib.rs

@@ -631,7 +631,10 @@ pub mod utils {
         }
     }
 
-    /// Discover KiCad files in a layout directory (errors if ambiguous).
+    /// Discover KiCad files in a layout directory by finding a single `.kicad_pro` file.
+    ///
+    /// The `.kicad_pcb` path is derived from the project file name. This avoids
+    /// false ambiguity from KiCad autosave files like `_autosave-layout.kicad_pcb`.
     pub fn discover_kicad_files(layout_dir: &Path) -> anyhow::Result<Option<KiCadLayoutFiles>> {
         if !layout_dir.exists() {
             return Ok(None);
@@ -641,7 +644,6 @@ pub mod utils {
         }
 
         let mut pro_path: Option<PathBuf> = None;
-        let mut pcb_path: Option<PathBuf> = None;
         for entry in fs::read_dir(layout_dir)
             .with_context(|| format!("Failed to read {}", layout_dir.display()))?
         {
@@ -650,48 +652,23 @@ pub mod utils {
                 continue;
             }
             let path = entry.path();
-            match path.extension().and_then(|s| s.to_str()) {
-                Some("kicad_pro") => {
-                    if pro_path.replace(path).is_some() {
-                        anyhow::bail!(
-                            "Multiple .kicad_pro files found in {}",
-                            layout_dir.display()
-                        );
-                    }
-                }
-                Some("kicad_pcb") => {
-                    if pcb_path.replace(path).is_some() {
-                        anyhow::bail!(
-                            "Multiple .kicad_pcb files found in {}",
-                            layout_dir.display()
-                        );
-                    }
-                }
-                _ => {}
+            if path.extension().and_then(|s| s.to_str()) == Some("kicad_pro")
+                && pro_path.replace(path).is_some()
+            {
+                anyhow::bail!(
+                    "Multiple .kicad_pro files found in {}",
+                    layout_dir.display()
+                );
             }
         }
 
-        if let Some(pro_path) = pro_path {
-            Ok(Some(KiCadLayoutFiles {
-                kicad_pro: pro_path,
-            }))
-        } else if let Some(pcb_path) = pcb_path {
-            Ok(Some(KiCadLayoutFiles {
-                kicad_pro: pcb_path.with_extension("kicad_pro"),
-            }))
-        } else {
-            Ok(None)
-        }
+        Ok(pro_path.map(|p| KiCadLayoutFiles { kicad_pro: p }))
     }
 
     /// Require a discoverable KiCad layout in `layout_dir`.
     pub fn require_kicad_files(layout_dir: &Path) -> anyhow::Result<KiCadLayoutFiles> {
-        discover_kicad_files(layout_dir)?.ok_or_else(|| {
-            anyhow::anyhow!(
-                "No .kicad_pro or .kicad_pcb found in {}",
-                layout_dir.display()
-            )
-        })
+        discover_kicad_files(layout_dir)?
+            .ok_or_else(|| anyhow::anyhow!("No .kicad_pro file found in {}", layout_dir.display()))
     }
 
     /// Resolve target file names for layout generation (defaults to `layout.*`).

crates/pcb-layout/src/scripts/lens/kicad_adapter.py

@@ -56,33 +56,25 @@
 def _discover_kicad_pcb_file(layout_dir: Path) -> Path:
     """Discover the KiCad PCB file inside a layout directory.
 
-    Prefers a single top-level `.kicad_pro` and derives `.kicad_pcb` by swapping
-    extension. Falls back to a single top-level `.kicad_pcb`. Errors on ambiguity.
+    Finds a single `.kicad_pro` file and derives the `.kicad_pcb` path from it.
+    This avoids false ambiguity from KiCad autosave files like
+    ``_autosave-layout.kicad_pcb``.
     """
     if not layout_dir.is_dir():
         raise FileNotFoundError(f"Layout fragment not found: {layout_dir}")
 
-    pro_files: List[Path] = []
-    pcb_files: List[Path] = []
-    for entry in layout_dir.iterdir():
-        if not entry.is_file():
-            continue
-        if entry.suffix == ".kicad_pro":
-            pro_files.append(entry)
-        elif entry.suffix == ".kicad_pcb":
-            pcb_files.append(entry)
+    pro_files: List[Path] = [
+        entry
+        for entry in layout_dir.iterdir()
+        if entry.is_file() and entry.suffix == ".kicad_pro"
+    ]
 
     if len(pro_files) > 1:
         raise ValueError(f"Multiple .kicad_pro files found in {layout_dir}")
     if len(pro_files) == 1:
         return pro_files[0].with_suffix(".kicad_pcb")
 
-    if len(pcb_files) > 1:
-        raise ValueError(f"Multiple .kicad_pcb files found in {layout_dir}")
-    if len(pcb_files) == 1:
-        return pcb_files[0]
-
-    raise FileNotFoundError(f"Layout fragment not found: {layout_dir}")
+    raise FileNotFoundError(f"No .kicad_pro file found in {layout_dir}")
 
 
 @dataclass(frozen=True)

crates/pcb/src/release.rs

@@ -631,8 +631,7 @@ fn discover_layout_from_output(
     };
     let layout_path = zen_parent_dir.join(clean_path_str);
 
-    // Discover KiCad files (accept a single top-level .kicad_pro or .kicad_pcb).
-    // If there are multiple candidates, treat it as an error (ambiguous).
+    // Discover KiCad files (require a single top-level .kicad_pro).
     let discovered = layout_utils::discover_kicad_files(&layout_path)?;
     if discovered.is_none() {
         if layout_path.exists() {