feat: add extra diagnostic block for coder metadata

Only `code` is present right now.

Author: Emyrk

types/diagnostics.go

@@ -6,6 +6,43 @@ import (
 	"github.com/hashicorp/hcl/v2"
 )
 
+type DiagnosticExtra struct {
+	Code string `json:"code"`
+
+	// If there was a previous extra, store it here for unwrapping.
+	wrapped any
+}
+
+var _ hcl.DiagnosticExtraUnwrapper = DiagnosticExtra{}
+
+func (e DiagnosticExtra) UnwrapDiagnosticExtra() interface{} {
+	return e.wrapped
+}
+
+func ExtractDiagnosticExtra(diag *hcl.Diagnostic) DiagnosticExtra {
+	// Zero values for a missing extra field is fine.
+	extra, _ := hcl.DiagnosticExtra[DiagnosticExtra](diag)
+	return extra
+}
+
+func SetDiagnosticExtra(diag *hcl.Diagnostic, extra DiagnosticExtra) {
+	existing, ok := hcl.DiagnosticExtra[DiagnosticExtra](diag)
+	if ok {
+		// If an existing extra is present, we will keep the underlying
+		// wrapped. This is not perfect, as any parents are lost.
+		// So try to avoid calling 'SetDiagnosticExtra' more than once.
+		extra.wrapped = existing.wrapped
+		diag.Extra = extra
+		return
+	}
+
+	// Maintain any existing extra fields.
+	if diag.Extra != nil {
+		extra.wrapped = diag.Extra
+	}
+	diag.Extra = extra
+}
+
 // Diagnostics is a JSON friendly form of hcl.Diagnostics.
 // Data is lost when doing a json marshal.
 type Diagnostics hcl.Diagnostics
@@ -23,11 +60,15 @@ func (d *Diagnostics) UnmarshalJSON(data []byte) error {
 			severity = hcl.DiagWarning
 		}
 
-		*d = append(*d, &hcl.Diagnostic{
+		hclDiag := &hcl.Diagnostic{
 			Severity: severity,
 			Summary:  diag.Summary,
 			Detail:   diag.Detail,
-		})
+		}
+
+		SetDiagnosticExtra(hclDiag, diag.Extra)
+
+		*d = append(*d, hclDiag)
 	}
 	return nil
 }
@@ -40,10 +81,13 @@ func (d Diagnostics) MarshalJSON() ([]byte, error) {
 			severity = DiagnosticSeverityWarning
 		}
 
+		extra := ExtractDiagnosticExtra(diag)
+
 		cpy = append(cpy, FriendlyDiagnostic{
 			Severity: severity,
 			Summary:  diag.Summary,
 			Detail:   diag.Detail,
+			Extra:    extra,
 		})
 	}
 	return json.Marshal(cpy)
@@ -60,4 +104,6 @@ type FriendlyDiagnostic struct {
 	Severity DiagnosticSeverityString `json:"severity"`
 	Summary  string                   `json:"summary"`
 	Detail   string                   `json:"detail"`
+
+	Extra DiagnosticExtra `json:"extra"`
 }

types/diagnostics_test.go

@@ -10,18 +10,48 @@ import (
 	"github.com/coder/preview/types"
 )
 
-func TestDiagnosticsJSON(t *testing.T) {
+func TestDiagnosticExtra(t *testing.T) {
+	diag := &hcl.Diagnostic{
+		Severity: hcl.DiagWarning,
+		Summary:  "Some summary",
+		Detail:   "Some detail",
+	}
+
+	extra := types.ExtractDiagnosticExtra(diag)
+	require.Empty(t, extra.Code)
+
+	// Set it
+	extra.Code = "foobar"
+	types.SetDiagnosticExtra(diag, extra)
+
+	extra = types.ExtractDiagnosticExtra(diag)
+	require.Equal(t, "foobar", extra.Code)
 
+	// Set it again
+	extra.Code = "bazz"
+	types.SetDiagnosticExtra(diag, extra)
+
+	extra = types.ExtractDiagnosticExtra(diag)
+	require.Equal(t, "bazz", extra.Code)
+}
+
+func TestDiagnosticsJSON(t *testing.T) {
 	diags := types.Diagnostics{
 		{
 			Severity: hcl.DiagWarning,
 			Summary:  "Some summary",
 			Detail:   "Some detail",
+			Extra: types.DiagnosticExtra{
+				Code: "foobar",
+			},
 		},
 		{
 			Severity: hcl.DiagError,
 			Summary:  "Some summary",
 			Detail:   "Some detail",
+			Extra: types.DiagnosticExtra{
+				Code: "",
+			},
 		},
 	}