bake: initial set of composable bake attributes

This allows using either the csv syntax or object syntax to specify
certain attributes.

This applies to the following fields:
- output
- cache-from
- cache-to
- secret
- ssh

There are still some remaining fields to translate. Specifically
ulimits, annotations, and attest.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

bake/hclparser/gohcl/schema_test.go

@@ -0,0 +1,233 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package gohcl
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/davecgh/go-spew/spew"
+	"github.com/hashicorp/hcl/v2"
+)
+
+func TestImpliedBodySchema(t *testing.T) {
+	tests := []struct {
+		val         interface{}
+		wantSchema  *hcl.BodySchema
+		wantPartial bool
+	}{
+		{
+			struct{}{},
+			&hcl.BodySchema{},
+			false,
+		},
+		{
+			struct {
+				Ignored bool
+			}{},
+			&hcl.BodySchema{},
+			false,
+		},
+		{
+			struct {
+				Attr1 bool `hcl:"attr1"`
+				Attr2 bool `hcl:"attr2"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "attr1",
+						Required: true,
+					},
+					{
+						Name:     "attr2",
+						Required: true,
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Attr *bool `hcl:"attr,attr"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "attr",
+						Required: false,
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Thing struct{} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type: "thing",
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Thing struct {
+					Type string `hcl:"type,label"`
+					Name string `hcl:"name,label"`
+				} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type:       "thing",
+						LabelNames: []string{"type", "name"},
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Thing []struct {
+					Type string `hcl:"type,label"`
+					Name string `hcl:"name,label"`
+				} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type:       "thing",
+						LabelNames: []string{"type", "name"},
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Thing *struct {
+					Type string `hcl:"type,label"`
+					Name string `hcl:"name,label"`
+				} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type:       "thing",
+						LabelNames: []string{"type", "name"},
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Thing struct {
+					Name      string `hcl:"name,label"`
+					Something string `hcl:"something"`
+				} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type:       "thing",
+						LabelNames: []string{"name"},
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Doodad string `hcl:"doodad"`
+				Thing  struct {
+					Name string `hcl:"name,label"`
+				} `hcl:"thing,block"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "doodad",
+						Required: true,
+					},
+				},
+				Blocks: []hcl.BlockHeaderSchema{
+					{
+						Type:       "thing",
+						LabelNames: []string{"name"},
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Doodad string `hcl:"doodad"`
+				Config string `hcl:",remain"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "doodad",
+						Required: true,
+					},
+				},
+			},
+			true,
+		},
+		{
+			struct {
+				Expr hcl.Expression `hcl:"expr"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "expr",
+						Required: false,
+					},
+				},
+			},
+			false,
+		},
+		{
+			struct {
+				Meh string `hcl:"meh,optional"`
+			}{},
+			&hcl.BodySchema{
+				Attributes: []hcl.AttributeSchema{
+					{
+						Name:     "meh",
+						Required: false,
+					},
+				},
+			},
+			false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%#v", test.val), func(t *testing.T) {
+			schema, partial := ImpliedBodySchema(test.val)
+			if !reflect.DeepEqual(schema, test.wantSchema) {
+				t.Errorf(
+					"wrong schema\ngot:  %s\nwant: %s",
+					spew.Sdump(schema), spew.Sdump(test.wantSchema),
+				)
+			}
+
+			if partial != test.wantPartial {
+				t.Errorf(
+					"wrong partial flag\ngot:  %#v\nwant: %#v",
+					partial, test.wantPartial,
+				)
+			}
+		})
+	}
+}