From fbaf4f88f7676a25603edf10f8b71447052eeaae Mon Sep 17 00:00:00 2001
From: CrazyMax <crazy-max@users.noreply.github.com>
Date: Tue, 24 Aug 2021 19:04:58 +0200
Subject: [PATCH] `platform` HCL func

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>
---
 bake/hclparser/builtin.go      | 21 +++++++++++++++++++++
 bake/hclparser/builtin_test.go | 14 ++++++++++++++
 bake/hclparser/hclparser.go    |  7 ++++++-
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 bake/hclparser/builtin.go
 create mode 100644 bake/hclparser/builtin_test.go

diff --git a/bake/hclparser/builtin.go b/bake/hclparser/builtin.go
new file mode 100644
index 000000000000..052f1e842d72
--- /dev/null
+++ b/bake/hclparser/builtin.go
@@ -0,0 +1,21 @@
+package hclparser
+
+import (
+	"github.com/containerd/containerd/platforms"
+	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/function"
+)
+
+var builtinFunctions = map[string]function.Function{
+	"platform": platformFunc,
+}
+
+// platformFunc returns the current platform's default
+// platform specification (e.g. linux/amd64).
+var platformFunc = function.New(&function.Spec{
+	Params: []function.Parameter{},
+	Type:   function.StaticReturnType(cty.String),
+	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		return cty.StringVal(platforms.DefaultString()), nil
+	},
+})
diff --git a/bake/hclparser/builtin_test.go b/bake/hclparser/builtin_test.go
new file mode 100644
index 000000000000..4c1da0f7929c
--- /dev/null
+++ b/bake/hclparser/builtin_test.go
@@ -0,0 +1,14 @@
+package hclparser
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPlatform(t *testing.T) {
+	p, err := platformFunc.Call(nil)
+	require.NoError(t, err)
+	assert.NotEmpty(t, p)
+}
diff --git a/bake/hclparser/hclparser.go b/bake/hclparser/hclparser.go
index 6438c7eb573c..fcb88d156521 100644
--- a/bake/hclparser/hclparser.go
+++ b/bake/hclparser/hclparser.go
@@ -262,6 +262,11 @@ func Parse(b hcl.Body, opt Opt, val interface{}) hcl.Diagnostics {
 		}
 	}
 
+	funcs := stdlibFunctions
+	for k, f := range builtinFunctions {
+		funcs[k] = f
+	}
+
 	p := &parser{
 		opt: opt,
 
@@ -274,7 +279,7 @@ func Parse(b hcl.Body, opt Opt, val interface{}) hcl.Diagnostics {
 		doneF:     map[string]struct{}{},
 		ectx: &hcl.EvalContext{
 			Variables: map[string]cty.Value{},
-			Functions: stdlibFunctions,
+			Functions: funcs,
 		},
 	}