Try to load manifest during spin build

crates/build/src/lib.rs

@@ -17,16 +17,31 @@ use crate::manifest::component_build_configs;
 
 /// If present, run the build command of each component.
 pub async fn build(manifest_file: &Path, component_ids: &[String]) -> Result<()> {
-    let components = component_build_configs(manifest_file)
-        .await
-        .with_context(|| {
-            format!(
-                "Cannot read manifest file from {}",
-                quoted_path(manifest_file)
-            )
-        })?;
+    let (components, manifest_err) =
+        component_build_configs(manifest_file)
+            .await
+            .with_context(|| {
+                format!(
+                    "Cannot read manifest file from {}",
+                    quoted_path(manifest_file)
+                )
+            })?;
     let app_dir = parent_dir(manifest_file)?;
 
+    let build_result = build_components(component_ids, components, app_dir);
+
+    if let Some(e) = manifest_err {
+        terminal::warn!("The manifest has errors not related to the Wasm component build. Error details:\n{e:#}");
+    }
+
+    build_result
+}
+
+fn build_components(
+    component_ids: &[String],
+    components: Vec<ComponentBuildInfo>,
+    app_dir: PathBuf,
+) -> Result<(), anyhow::Error> {
     let components_to_build = if component_ids.is_empty() {
         components
     } else {

crates/build/src/manifest.rs

@@ -5,9 +5,36 @@ use std::{collections::BTreeMap, path::Path};
 use spin_manifest::{schema::v2, ManifestVersion};
 
 /// Returns a map of component IDs to [`v2::ComponentBuildConfig`]s for the
-/// given (v1 or v2) manifest path.
+/// given (v1 or v2) manifest path. If the manifest cannot be loaded, the
+/// function attempts fallback: if fallback succeeds, result is Ok but the load error
+/// is also returned via the second part of the return value tuple.
 pub async fn component_build_configs(
     manifest_file: impl AsRef<Path>,
+) -> Result<(Vec<ComponentBuildInfo>, Option<spin_manifest::Error>)> {
+    let manifest = spin_manifest::manifest_from_file(&manifest_file);
+    match manifest {
+        Ok(manifest) => Ok((build_configs_from_manifest(manifest), None)),
+        Err(e) => fallback_load_build_configs(&manifest_file)
+            .await
+            .map(|bc| (bc, Some(e))),
+    }
+}
+
+fn build_configs_from_manifest(
+    manifest: spin_manifest::schema::v2::AppManifest,
+) -> Vec<ComponentBuildInfo> {
+    manifest
+        .components
+        .into_iter()
+        .map(|(id, c)| ComponentBuildInfo {
+            id: id.to_string(),
+            build: c.build,
+        })
+        .collect()
+}
+
+async fn fallback_load_build_configs(
+    manifest_file: impl AsRef<Path>,
 ) -> Result<Vec<ComponentBuildInfo>> {
     let manifest_text = tokio::fs::read_to_string(manifest_file).await?;
     Ok(match ManifestVersion::detect(&manifest_text)? {