feat context: Add ability to import extra variables from files

Kontemplate context specifications can now load extra variables from YAML
or JSON files by specifying a list of files (relative to the context file)
under the `import` key.

6 files changed, 96 insertions, 4 deletions

diff --git a/context/context.go b/context/context.go
index 0dde5905561d..c812af8b26f7 100644
--- a/context/context.go
+++ b/context/context.go
@@ -17,10 +17,11 @@ type ResourceSet struct {
 }
 
 type Context struct {
-	Name         string                 `json:"context"`
-	Global       map[string]interface{} `json:"global"`
-	ResourceSets []ResourceSet          `json:"include"`
-	BaseDir      string
+	Name            string                 `json:"context"`
+	Global          map[string]interface{} `json:"global"`
+	ResourceSets    []ResourceSet          `json:"include"`
+	VariableImports []string               `json:"import"`
+	BaseDir         string
 }
 
 type ContextLoadingError struct {
@@ -44,9 +45,34 @@ func LoadContextFromFile(filename string) (*Context, error) {
 	c.BaseDir = path.Dir(filename)
 	c.ResourceSets = loadAllDefaultValues(&c)
 
+	err = c.loadImportedVariables()
+	if err != nil {
+		return nil, meep.New(
+			&ContextLoadingError{Filename: filename},
+			meep.Cause(err),
+		)
+	}
+
 	return &c, nil
 }
 
+// Kontemplate supports specifying additional variable files with the `import` keyword. This function loads those
+// variable files and merges them together with the context's other global variables.
+func (ctx *Context) loadImportedVariables() error {
+	for _, file := range ctx.VariableImports {
+		var importedVars map[string]interface{}
+		err := util.LoadJsonOrYaml(path.Join(ctx.BaseDir, file), &importedVars)
+
+		if err != nil {
+			return err
+		}
+
+		ctx.Global = *util.Merge(&ctx.Global, &importedVars)
+	}
+
+	return nil
+}
+
 // Flattens resource set collections, i.e. resource sets that themselves have an additional 'include' field set.
 // Those will be regarded as a short-hand for including multiple resource sets from a subfolder.
 // See https://github.com/tazjin/kontemplate/issues/9 for more information.
diff --git a/context/context_test.go b/context/context_test.go
index c5b5e7f12611..b6acf416e6cc 100644
--- a/context/context_test.go
+++ b/context/context_test.go
@@ -159,3 +159,47 @@ func TestDefaultValuesLoading(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func TestImportValuesLoading(t *testing.T) {
+	ctx, err := LoadContextFromFile("testdata/import-vars-simple.yaml")
+	if err != nil {
+		t.Error(err)
+		t.Fail()
+	}
+
+	expected := map[string]interface{}{
+		"override": "true",
+		"music": map[string]interface{}{
+			"artist": "Pallida",
+			"track":  "Tractor Beam",
+		},
+	}
+
+	if !reflect.DeepEqual(ctx.Global, expected) {
+		t.Error("Expected global values after loading imports did not match!")
+		t.Fail()
+	}
+}
+
+func TestImportValuesOverride(t *testing.T) {
+	ctx, err := LoadContextFromFile("testdata/import-vars-override.yaml")
+	if err != nil {
+		t.Error(err)
+		t.Fail()
+	}
+
+	expected := map[string]interface{}{
+		"override": float64(3),
+		"music": map[string]interface{}{
+			"artist": "Pallida",
+			"track":  "Tractor Beam",
+		},
+		"place":     "Oslo",
+		"globalVar": "very global!",
+	}
+
+	if !reflect.DeepEqual(ctx.Global, expected) {
+		t.Error("Expected global values after loading imports did not match!")
+		t.Fail()
+	}
+}
diff --git a/context/testdata/import-vars-override.yaml b/context/testdata/import-vars-override.yaml
new file mode 100644
index 000000000000..c3d47bcfc1fc
--- /dev/null
+++ b/context/testdata/import-vars-override.yaml
@@ -0,0 +1,9 @@
+---
+context: k8s.prod.mydomain.com
+global:
+  globalVar: very global!
+  override: 1
+import:
+  - test-vars.yaml
+  - test-vars-override.yaml
+include: []
diff --git a/context/testdata/import-vars-simple.yaml b/context/testdata/import-vars-simple.yaml
new file mode 100644
index 000000000000..12244e1ab174
--- /dev/null
+++ b/context/testdata/import-vars-simple.yaml
@@ -0,0 +1,5 @@
+---
+context: k8s.prod.mydomain.com
+import:
+  - test-vars.yaml
+include: []
diff --git a/context/testdata/test-vars-override.yaml b/context/testdata/test-vars-override.yaml
new file mode 100644
index 000000000000..5215c559c136
--- /dev/null
+++ b/context/testdata/test-vars-override.yaml
@@ -0,0 +1,3 @@
+---
+override: 3
+place: Oslo
diff --git a/context/testdata/test-vars.yaml b/context/testdata/test-vars.yaml
new file mode 100644
index 000000000000..af27bdc455bf
--- /dev/null
+++ b/context/testdata/test-vars.yaml
@@ -0,0 +1,5 @@
+---
+override: 'true'
+music:
+  artist: Pallida
+  track: Tractor Beam