deb: auto-inject shlibs:depends and misc:depends

These are dependencies that will be resolved automatically by debbuild.
If they are not needed then the resulting control file that is output by
debbuild will not include anything extra.
However, when the dependencies are needed it is important to have them.

This helps keep the spec more generic and avoid making mistakes.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

frontend/deb/template_control.go

@@ -4,6 +4,7 @@ import (
 	_ "embed"
 	"fmt"
 	"io"
+	"maps"
 	"strings"
 	"text/template"
 
@@ -57,13 +58,46 @@ func appendConstraints(deps map[string]dalec.PackageConstraints) []string {
 }
 
 func (w *controlWrapper) depends(buf io.Writer, depsSpec *dalec.PackageDependencies) {
-	if len(depsSpec.Runtime) == 0 {
-		return
+	var (
+		needsClone bool
+		rtDeps     map[string]dalec.PackageConstraints
+	)
+	if depsSpec == nil || depsSpec.Runtime == nil {
+		rtDeps = make(map[string]dalec.PackageConstraints)
+	} else {
+		rtDeps = depsSpec.Runtime
+		needsClone = true
 	}
 
-	deps := appendConstraints(depsSpec.Runtime)
-	fmt.Fprintln(buf, multiline("Depends", deps))
+	// Add in deps vars that will get resolved by debbuild
+	// In some cases these are not neccessary (maybe even most), but when they are
+	// it is important.
+	// When not needed lintian may throw warnings but that's ok.
+	// If these aren't actually needed they'll resolve to nothing and don't cause
+	// any changes.
+	const (
+		shlibsDeps = "${shlibs:Depends}"
+		miscDeps   = "${misc:Depends}"
+	)
+
+	if _, exists := rtDeps[shlibsDeps]; !exists {
+		if needsClone {
+			rtDeps = maps.Clone(rtDeps)
+			needsClone = false
+		}
+
+		rtDeps[shlibsDeps] = dalec.PackageConstraints{}
+	}
 
+	if _, exists := rtDeps[miscDeps]; !exists {
+		if needsClone {
+			rtDeps = maps.Clone(rtDeps)
+		}
+		rtDeps[miscDeps] = dalec.PackageConstraints{}
+	}
+
+	deps := appendConstraints(rtDeps)
+	fmt.Fprintln(buf, multiline("Depends", deps))
 }
 
 // multiline attempts to format a field with multiple values in a way that is more human readable

frontend/deb/template_rules_test.go

@@ -1,10 +1,13 @@
 package deb
 
 import (
+	"bytes"
+	"strings"
 	"testing"
 
 	"github.com/Azure/dalec"
 	"gotest.tools/v3/assert"
+	"gotest.tools/v3/assert/cmp"
 )
 
 func TestRules_OverrideSystemd(t *testing.T) {
@@ -109,3 +112,81 @@ func TestRules_OverrideSystemd(t *testing.T) {
 		})
 	})
 }
+
+func TestDepends(t *testing.T) {
+	control := &controlWrapper{}
+
+	buf := bytes.NewBuffer(nil)
+	control.depends(buf, nil)
+
+	expect := `
+Depends: ${misc:Depends},
+         ${shlibs:Depends}
+`
+	actual := strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+
+	buf.Reset()
+
+	// Test again with non-nil deps
+	control.depends(buf, &dalec.PackageDependencies{})
+	actual = strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+
+	buf.Reset()
+
+	// Test again with non-nil runtime deps
+	control.depends(buf, &dalec.PackageDependencies{
+		Runtime: map[string]dalec.PackageConstraints{},
+	})
+	actual = strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+
+	buf.Reset()
+
+	// Test again with other runtime deps
+	control.depends(buf, &dalec.PackageDependencies{
+		Runtime: map[string]dalec.PackageConstraints{
+			"foo": {},
+			"bar": {},
+		},
+	})
+
+	expect = `
+Depends: ${misc:Depends},
+         ${shlibs:Depends},
+         bar,
+         foo
+`
+	actual = strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+
+	buf.Reset()
+
+	// Test again with other runtime deps and shlibs specified
+	control.depends(buf, &dalec.PackageDependencies{
+		Runtime: map[string]dalec.PackageConstraints{
+			"foo":               {},
+			"bar":               {},
+			"${shlibs:Depends}": {},
+		},
+	})
+
+	actual = strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+
+	buf.Reset()
+
+	// Test again with other runtime deps and shlibs and misc depends specified
+	control.depends(buf, &dalec.PackageDependencies{
+		Runtime: map[string]dalec.PackageConstraints{
+			"foo":               {},
+			"bar":               {},
+			"${shlibs:Depends}": {},
+			"${misc:Depends}":   {},
+		},
+	})
+
+	actual = strings.TrimSpace(buf.String())
+	assert.Check(t, cmp.Equal(actual, strings.TrimSpace(expect)))
+}