feat: ValidatePrebuilds to validate presets for prebuild use (#194)

Presets were being created with prebuild counts, even if the preset was
unable to be used for a prebuild. This creates a function that can
validate prebuilds.

Author: Emyrk

extract/preset.go

@@ -1,12 +1,34 @@
 package extract
 
 import (
+	"fmt"
+
 	"github.com/aquasecurity/trivy/pkg/iac/terraform"
-	"github.com/coder/preview/types"
 	"github.com/hashicorp/hcl/v2"
+
+	"github.com/coder/preview/types"
 )
 
-func PresetFromBlock(block *terraform.Block) types.Preset {
+func PresetFromBlock(block *terraform.Block) (tfPreset types.Preset) {
+	defer func() {
+		// Extra safety mechanism to ensure that if a panic occurs, we do not break
+		// everything else.
+		if r := recover(); r != nil {
+			tfPreset = types.Preset{
+				PresetData: types.PresetData{
+					Name: block.Label(),
+				},
+				Diagnostics: types.Diagnostics{
+					{
+						Severity: hcl.DiagError,
+						Summary:  "Panic occurred in extracting preset. This should not happen, please report this to Coder.",
+						Detail:   fmt.Sprintf("panic in preset extract: %+v", r),
+					},
+				},
+			}
+		}
+	}()
+
 	p := types.Preset{
 		PresetData: types.PresetData{
 			Parameters: make(map[string]string),
@@ -41,5 +63,13 @@ func PresetFromBlock(block *terraform.Block) types.Preset {
 		p.Default = defaultAttr.Value().True()
 	}
 
+	prebuildBlock := block.GetBlock("prebuilds")
+	if prebuildBlock != nil {
+		p.Prebuilds = &types.PrebuildData{
+			// Invalid values will be set to 0
+			Instances: int(optionalInteger(prebuildBlock, "instances")),
+		}
+	}
+
 	return p
 }

preview.go

@@ -68,6 +68,61 @@ func (o Output) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// ValidatePrebuilds will iterate over each preset, validate the inputs as a set,
+// and attach any diagnostics to the preset if there are issues. This must be done
+// because prebuilds have to be valid without user input.
+//
+// This will only validate presets that have prebuilds configured and have no
+// existing error diagnostics. This should only be used when doing Template
+// Imports as a protection against invalid presets.
+//
+// A preset doesn't need to specify all required parameters, as users can provide
+// the remaining values when creating a workspace. However, since prebuild
+// creation has no user input, presets used for prebuilds must provide all
+// required parameter values.
+func ValidatePrebuilds(ctx context.Context, input Input, preValid []types.Preset, dir fs.FS) {
+	for i := range preValid {
+		pre := &preValid[i]
+		if pre.Prebuilds == nil || pre.Prebuilds.Instances <= 0 {
+			// No prebuilds, so presets do not need to be valid without user input
+			continue
+		}
+
+		if hcl.Diagnostics(pre.Diagnostics).HasErrors() {
+			// Piling on diagnostics is not helpful, if an error exists, leave it at that.
+			continue
+		}
+
+		// Diagnostics are added to the existing preset.
+		input.ParameterValues = pre.Parameters
+		output, diagnostics := Preview(ctx, input, dir)
+		if diagnostics.HasErrors() {
+			pre.Diagnostics = append(pre.Diagnostics, diagnostics...)
+			// Do not pile on more diagnostics for individual params, it already failed
+			continue
+		}
+
+		if output == nil {
+			continue
+		}
+
+		// If any parameter is invalid, then the preset is invalid.
+		// A value must be specified for this failing parameter.
+		for _, param := range output.Parameters {
+			if hcl.Diagnostics(param.Diagnostics).HasErrors() {
+				for _, paramDiag := range param.Diagnostics {
+					if paramDiag.Severity != hcl.DiagError {
+						continue // Only care about errors here
+					}
+					orig := paramDiag.Summary
+					paramDiag.Summary = fmt.Sprintf("Parameter %s: %s", param.Name, orig)
+					pre.Diagnostics = append(pre.Diagnostics, paramDiag)
+				}
+			}
+		}
+	}
+}
+
 func Preview(ctx context.Context, input Input, dir fs.FS) (output *Output, diagnostics hcl.Diagnostics) {
 	// The trivy package works with `github.com/zclconf/go-cty`. This package is
 	// similar to `reflect` in its usage. This package can panic if types are
@@ -180,7 +235,9 @@ func Preview(ctx context.Context, input Input, dir fs.FS) (output *Output, diagn
 
 	diags := make(hcl.Diagnostics, 0)
 	rp, rpDiags := parameters(modules)
-	presets := presets(modules, rp)
+	// preValidPresets are extracted as written in terraform. Each individual
+	// param value is checked, however, the preset as a whole might not be valid.
+	preValidPresets := presets(modules, rp)
 	tags, tagDiags := workspaceTags(modules, p.Files())
 	vars := variables(modules)
 
@@ -191,7 +248,7 @@ func Preview(ctx context.Context, input Input, dir fs.FS) (output *Output, diagn
 		ModuleOutput:  outputs,
 		Parameters:    rp,
 		WorkspaceTags: tags,
-		Presets:       presets,
+		Presets:       preValidPresets,
 		Files:         p.Files(),
 		Variables:     vars,
 	}, diags.Extend(rpDiags).Extend(tagDiags)