Add vintner doctor for diagnosing a broken wine/toolchain setup

A misconfigured environment (wine missing, msitools not installed, a
partially-built toolchain) otherwise only surfaces as a wine-specific
error buried deep inside a build. `vintner doctor` checks wine itself
(found and actually runs), the optional extraction tools download
needs, and every installed <dest>/bin/<arch> toolchain's on-disk
layout, printing a pass/fail checklist and exiting non-zero if
anything's broken.

cmd/vintner/doctor_test.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/Cheviiot/vintner/internal/wineenv"
+)
+
+func TestRunDoctorUsage(t *testing.T) {
+	for _, flag := range []string{"-h", "--help"} {
+		if code := runDoctor([]string{flag}); code != 1 {
+			t.Errorf("runDoctor([%q]) = %d, want 1", flag, code)
+		}
+	}
+}
+
+func TestDoctorReportOkWarnFail(t *testing.T) {
+	d := &doctorReport{}
+	d.ok("fine")
+	d.warn("meh")
+	if d.failed {
+		t.Fatal("ok/warn must not mark the report as failed")
+	}
+	d.fail("broken")
+	if !d.failed {
+		t.Fatal("fail must mark the report as failed")
+	}
+}
+
+func TestInstalledArchDirsFindsOnlyDirsWithEnvJSON(t *testing.T) {
+	destBin := t.TempDir()
+	for _, dir := range []string{"x64", "x86", "not-a-toolchain"} {
+		if err := os.MkdirAll(filepath.Join(destBin, dir), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, dir := range []string{"x64", "x86"} {
+		if err := os.WriteFile(filepath.Join(destBin, dir, wineenv.ConfigFileName), []byte("{}"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	got := installedArchDirs(destBin)
+	want := map[string]bool{"x64": true, "x86": true}
+	if len(got) != len(want) {
+		t.Fatalf("installedArchDirs = %v, want exactly %v", got, want)
+	}
+	for _, arch := range got {
+		if !want[arch] {
+			t.Errorf("installedArchDirs returned unexpected entry %q", arch)
+		}
+	}
+}
+
+func TestInstalledArchDirsMissingDir(t *testing.T) {
+	if got := installedArchDirs(filepath.Join(t.TempDir(), "does-not-exist")); got != nil {
+		t.Errorf("installedArchDirs on a missing dir = %v, want nil", got)
+	}
+}
+
+func TestCheckToolchainAtMissingEnvJSON(t *testing.T) {
+	d := &doctorReport{}
+	d.checkToolchainAt(t.TempDir(), "test")
+	if !d.failed {
+		t.Error("checkToolchainAt against a dir with no env.json should fail the report")
+	}
+}
+
+func TestTrimNewline(t *testing.T) {
+	cases := map[string]string{
+		"wine-9.0\n":   "wine-9.0",
+		"wine-9.0\r\n": "wine-9.0",
+		"wine-9.0":     "wine-9.0",
+		"":             "",
+	}
+	for in, want := range cases {
+		if got := trimNewline(in); got != want {
+			t.Errorf("trimNewline(%q) = %q, want %q", in, got, want)
+		}
+	}
+}