[nix] Fix StorePathsAreInStore (#2104)

## Summary

Addresses issue introduced in 

#2076
and
#2098

Basically we have 2 different uses cases when looking up store paths.
Sometimes we want all store paths (whether installed or not) and in
other cases we only want paths that are in local store. This change
fixes that and adds some testing.

## How was it tested?

unit tests, manual integration test by installing a package that was not
in local store.

internal/nix/store.go

@@ -49,12 +49,12 @@ func StorePathsFromInstallable(ctx context.Context, installable string, allowIns
 		return nil, err
 	}
 
-	validPaths, err := parseStorePathFromInstallableOutput(resultBytes)
+	paths, err := parseStorePathFromInstallableOutput(resultBytes)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse path-info for %s: %w", installable, err)
 	}
 
-	return maps.Keys(validPaths), nil
+	return maps.Keys(paths), nil
 }
 
 // StorePathsAreInStore a map of store paths to whether they are in the store.
@@ -71,44 +71,39 @@ func StorePathsAreInStore(ctx context.Context, storePaths []string) (map[string]
 		return nil, err
 	}
 
-	validPaths, err := parseStorePathFromInstallableOutput(output)
-	if err != nil {
-		return nil, err
-	}
-
-	result := map[string]bool{}
-	for _, storePath := range storePaths {
-		_, ok := validPaths[storePath]
-		result[storePath] = ok
-	}
-
-	return result, nil
+	return parseStorePathFromInstallableOutput(output)
 }
 
 // Older nix versions (like 2.17) are an array of objects that contain path and valid fields
-type pathInfoLegacy struct {
-	Path string `json:"path"`
+type LegacyPathInfo struct {
+	Path  string `json:"path"`
+	Valid bool   `json:"valid"` // this means path is in store
 }
 
 // parseStorePathFromInstallableOutput parses the output of `nix store path-from-installable --json`
+// into a map of store paths to whether they are in the store.
 // This function is decomposed out of StorePathFromInstallable to make it testable.
-func parseStorePathFromInstallableOutput(output []byte) (map[string]any, error) {
+func parseStorePathFromInstallableOutput(output []byte) (map[string]bool, error) {
+	result := map[string]bool{}
+
 	// Newer nix versions (like 2.20) have output of the form
 	// {"<store-path>": {}}
 	// Note that values will be null if paths are not in store.
-	var out1 map[string]any
-	if err := json.Unmarshal(output, &out1); err == nil {
-		return out1, nil
+	var modernPathInfo map[string]any
+	if err := json.Unmarshal(output, &modernPathInfo); err == nil {
+		for path, val := range modernPathInfo {
+			result[path] = val != nil
+		}
+		return result, nil
 	}
 
-	var out2 []pathInfoLegacy
+	var legacyPathInfos []LegacyPathInfo
 
-	if err := json.Unmarshal(output, &out2); err == nil {
-		res := map[string]any{}
-		for _, outValue := range out2 {
-			res[outValue.Path] = true
+	if err := json.Unmarshal(output, &legacyPathInfos); err == nil {
+		for _, outValue := range legacyPathInfos {
+			result[outValue.Path] = outValue.Valid
 		}
-		return res, nil
+		return result, nil
 	}
 
 	return nil, fmt.Errorf("failed to parse path-info output: %s", output)

internal/nix/store_test.go

@@ -1,7 +1,6 @@
 package nix
 
 import (
-	"slices"
 	"testing"
 
 	"golang.org/x/exp/maps"
@@ -11,18 +10,37 @@ func TestParseStorePathFromInstallableOutput(t *testing.T) {
 	testCases := []struct {
 		name     string
 		input    string
-		expected []string
+		expected map[string]bool
 	}{
 		{
 			name: "go-basic-nix-2-20-1",
 			// snipped the actual output for brevity. We mainly care about the first key in the JSON.
-			input:    `{"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0":{"deriver":"/nix/store/clr3bm8njqysvyw4r4x4xmldhz4knrff-go-1.22.0.drv"}}`,
-			expected: []string{"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0"},
+			input: `{"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0":{"deriver":"/nix/store/clr3bm8njqysvyw4r4x4xmldhz4knrff-go-1.22.0.drv"}}`,
+			expected: map[string]bool{
+				"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0": true,
+			},
 		},
 		{
-			name:     "go-basic-nix-2-17-0",
-			input:    `[{"path":"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0"}]`,
-			expected: []string{"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0"},
+			name: "go-basic-nix-2-20-1",
+			// snipped the actual output for brevity. We mainly care about the first key in the JSON.
+			input: `{"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0":null}`,
+			expected: map[string]bool{
+				"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0": false,
+			},
+		},
+		{
+			name:  "go-basic-nix-2-17-0",
+			input: `[{"path":"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0"}]`,
+			expected: map[string]bool{
+				"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0": false,
+			},
+		},
+		{
+			name:  "go-basic-nix-2-17-0",
+			input: `[{"path":"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0", "valid": true}]`,
+			expected: map[string]bool{
+				"/nix/store/fgkl3qk8p5hnd07b0dhzfky3ys5gxjmq-go-1.22.0": true,
+			},
 		},
 	}
 
@@ -32,8 +50,8 @@ func TestParseStorePathFromInstallableOutput(t *testing.T) {
 			if err != nil {
 				t.Errorf("Expected no error but got error: %s", err)
 			}
-			if !slices.Equal(tc.expected, maps.Keys(actual)) {
-				t.Errorf("Expected store path %s but got %s", tc.expected, actual)
+			if !maps.Equal(tc.expected, actual) {
+				t.Errorf("Expected store path %v but got %v", tc.expected, actual)
 			}
 		})
 	}