Incorporate arch into BestKey

With the `--nobest` option disabled (the default), the loader permitted only one RPM candidate per package name, selected via repository priority and version.
This logic is intended to prune suboptimal version early; failure to resolve after the prune usually indicates repository issues.

However, when multiple architectures are enabled, this filtering can cause resolution failures even with a valid repository state.
Specifically, if a dependency requires a package from a secondary architecture (e.g. i686 on an x86_64 system), but the primary architecture variant is considered "better", the required variant is discarded before the solver can consider it.

This change ensures that the "best" candidate is calculated independently for each architecture.

Explicitly requested packages remain constrained to their "best" version (including best matching architecture), but the dependency tree gains the necessary flexibility to resolve architecture-sensitive requirements.

Author: aszady

pkg/sat/loader.go

@@ -28,17 +28,19 @@ type Loader struct {
 // (best in terms of repo priority, version criteria).
 type BestKey struct {
 	name string
+	arch string
 }
 
 // CompareBestKey provides an arbitrary, deterministic, total order on BestKey
 func CompareBestKey(k1 BestKey, k2 BestKey) int {
 	return cmp.Or(
 		cmp.Compare(k1.name, k2.name),
+		cmp.Compare(k1.arch, k2.arch),
 	)
 }
 
 func MakeBestKey(pkg *api.Package) BestKey {
-	return BestKey{name: pkg.Name}
+	return BestKey{name: pkg.Name, arch: pkg.Arch}
 }
 
 func NewLoader() *Loader {

pkg/sat/sat_test.go

@@ -1429,7 +1429,7 @@ func TestNewResolver(t *testing.T) {
 			"testa",
 		},
 			install:  []string{"testa-0:2.x86_64"},
-			exclude:  []string{},
+			exclude:  []string{"testa-0:3.noarch"},
 			solvable: true,
 		},
 		{name: "prioritize dependency: best arch & version", packages: []*api.Package{
@@ -1443,7 +1443,7 @@ func TestNewResolver(t *testing.T) {
 			"testa",
 		},
 			install:  []string{"testa-0:1.noarch", "testb-0:2.x86_64"},
-			exclude:  []string{},
+			exclude:  []string{"testb-0:3.noarch"},
 			solvable: true,
 		},
 		{name: "cross-arch dependency (by name and by resource)", packages: []*api.Package{
@@ -1478,9 +1478,21 @@ func TestNewResolver(t *testing.T) {
 			"testa",
 		},
 			install:  []string{"testa-0:1.x86_64", "testb-0:1.x86_64"},
-			exclude:  []string{},
+			exclude:  []string{"testa-0:1.noarch", "testb-0:1.noarch"},
 			solvable: true,
 		},
+		{name: "dependency on non-primary architecture", packages: []*api.Package{
+			newPkgAP("testa", "1", "noarch", 1, []string{}, []string{"/usr/lib/libb.so"}, []string{}),
+			newPkgAP("testb", "1", "x86_64", 1, []string{"/usr/lib64/libb.so"}, []string{}, []string{}),
+			newPkgAP("testb", "1", "i686", 1, []string{"/usr/lib/libb.so"}, []string{}, []string{}),
+		}, requires: []string{
+			"testa",
+		},
+			architectures: []string{"x86_64", "i686"},
+			install:       []string{"testa-0:1.noarch", "testb-0:1.i686"},
+			exclude:       []string{"testb-0:1.x86_64"},
+			solvable:      true,
+		},
 
 		// TODO: Add test cases.
 	}