dnfjson: allow (optional) field solver in the dnfjson output

With the new "dnf5" solver is seems useful to allow the dnfjson
code return what solver was actually used in the transaction.

This commit allows an (optional) "solver" field in the json
that is returned from the dnfjson helper. It does not do more
yet but we should (probably) make it avaialble for the higher
layers too so that it can be e.g. logged.

See also osbuild/osbuild#1776

Co-authored-by: Achilleas Koutsou <[email protected]>

pkg/dnfjson/dnfjson.go

@@ -690,6 +690,9 @@ type packageSpecs []PackageSpec
 type depsolveResult struct {
 	Packages packageSpecs          `json:"packages"`
 	Repos    map[string]repoConfig `json:"repos"`
+
+	// (optional) contains the solver used, e.g. "dnf5"
+	Solver string `json:"solver"`
 }
 
 // Package specification

pkg/dnfjson/dnfjson_test.go

@@ -788,3 +788,29 @@ exit 1
 	_, err = run([]string{fakeDnfJsonPath}, &Request{})
 	assert.EqualError(t, err, `DNF error occurred: InternalError: dnf-json output was empty`)
 }
+
+func TestSolverRunWithSolverNoError(t *testing.T) {
+	tmpdir := t.TempDir()
+	fakeSolver := `#!/bin/sh -e
+cat - > "$0".stdin
+echo '{"solver": "zypper"}'
+`
+	fakeSolverPath := filepath.Join(tmpdir, "fake-solver")
+	err := os.WriteFile(fakeSolverPath, []byte(fakeSolver), 0755) //nolint:gosec
+	assert.NoError(t, err)
+
+	solver := NewSolver("platform:f38", "38", "x86_64", "fedora-38", "/tmp/cache")
+	solver.dnfJsonCmd = []string{fakeSolverPath}
+	pkgSpec, repoCfg, err := solver.Depsolve(nil)
+	assert.NoError(t, err)
+
+	// prerequisite check, i.e. ensure our fake was called in the right way
+	stdin, err := os.ReadFile(fakeSolverPath + ".stdin")
+	assert.NoError(t, err)
+	assert.Contains(t, string(stdin), `"command":"depsolve"`)
+
+	// adding the "solver" did not cause any issues
+	assert.NoError(t, err)
+	assert.Equal(t, 0, len(pkgSpec))
+	assert.Equal(t, 0, len(repoCfg))
+}