projects/projectconfigs: decode "upstream" block contents

projects/projectconfigs/config.go

@@ -33,6 +33,7 @@ type Config struct {
 	Context    map[string]*ContextValue
 	Locals     map[string]*LocalValue
 	Workspaces map[string]*Workspace
+	Upstreams  map[string]*Upstream
 }
 
 func loadConfigDir(rootDir string) (*Config, tfdiags.Diagnostics) {
@@ -187,6 +188,25 @@ func loadConfig(rootDir, filename string, src []byte, body hcl.Body) (*Config, t
 
 				config.Workspaces[ws.Name] = ws
 			}
+
+		case "upstream":
+			u, moreDiags := decodeUpstreamBlock(block)
+			diags = diags.Append(moreDiags)
+			if u != nil {
+				if existing, exists := config.Upstreams[u.Name]; exists {
+					diags = diags.Append(&hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Duplicate \"upstream\" block",
+						Detail:   fmt.Sprintf("An upstream %q block was already declared at %s.", u.Name, existing.DeclRange.StartString()),
+						Subject:  u.NameRange.ToHCL().Ptr(),
+						Context:  u.DeclRange.ToHCL().Ptr(),
+					})
+					continue
+				}
+
+				config.Upstreams[u.Name] = u
+			}
+
 		default:
 			// No other block types in our schema, so anything else is a bug.
 			panic(fmt.Sprintf("unexpected block type %q", block.Type))
@@ -201,5 +221,6 @@ var rootSchema = &hcl.BodySchema{
 		{Type: "context", LabelNames: []string{"name"}},
 		{Type: "locals"},
 		{Type: "workspace", LabelNames: []string{"name"}},
+		{Type: "upstream", LabelNames: []string{"name"}},
 	},
 }

projects/projectconfigs/upstream.go

@@ -0,0 +1,69 @@
+package projectconfigs
+
+import (
+	"fmt"
+
+	"github.com/hashicorp/hcl2/hcl"
+	"github.com/hashicorp/hcl2/hcl/hclsyntax"
+
+	"github.com/hashicorp/terraform/tfdiags"
+)
+
+// Upstream represents a remote workspace from another project that this
+// project derives values from.
+type Upstream struct {
+	// Name is the name label given in the block header.
+	//
+	// It is guaranteed to be a valid HCL identifier.
+	Name string
+
+	// ForEach is the expression given in the for_each argument, or nil if
+	// that argument wasn't set.
+	ForEach hcl.Expression
+
+	// Remote is the expression given in the "remote" argument.
+	Remote hcl.Expression
+
+	// DeclRange is the source range of the block header of this block,
+	// for use in diagnostic messages. NameRange is the range of the
+	// Name string specifically.
+	DeclRange, NameRange tfdiags.SourceRange
+}
+
+func decodeUpstreamBlock(block *hcl.Block) (*Upstream, tfdiags.Diagnostics) {
+	var diags tfdiags.Diagnostics
+	u := &Upstream{
+		Name:      block.Labels[0],
+		DeclRange: tfdiags.SourceRangeFromHCL(block.DefRange),
+		NameRange: tfdiags.SourceRangeFromHCL(block.LabelRanges[0]),
+	}
+
+	if !hclsyntax.ValidIdentifier(u.Name) {
+		diags = diags.Append(&hcl.Diagnostic{
+			Severity: hcl.DiagError,
+			Summary:  "Invalid name for \"upstream\" block",
+			Detail:   fmt.Sprintf("The name %q is not a valid name for an \"upstream\" block. Must start with a letter, followed by zero or more letters, digits, and underscores.", u.Name),
+			Subject:  block.LabelRanges[0].Ptr(),
+		})
+	}
+
+	content, hclDiags := block.Body.Content(workspaceSchema)
+	diags = diags.Append(hclDiags)
+
+	if attr, ok := content.Attributes["for_each"]; ok {
+		u.ForEach = attr.Expr
+	}
+
+	if attr, ok := content.Attributes["remote"]; ok {
+		u.Remote = attr.Expr
+	}
+
+	return u, diags
+}
+
+var upstreamSchema = &hcl.BodySchema{
+	Attributes: []hcl.AttributeSchema{
+		{Name: "for_each"},
+		{Name: "remote", Required: true},
+	},
+}