chore: remove all possible AsString panics (#183)

Any call to `AsString` is unsafe. All places where the error is ignored
is used in errors, so a placeholder or empty string is ok.

A panic was observed by a customer. I am not sure where it occured. To
be safe, I am using the function we have to protect these `AsString`
calls. I added a custom linter to prevent these calls, this PR just
removes all calls that were not fixed already.

Author: Emyrk

extract/parameter.go

@@ -267,6 +267,7 @@ func optionalStringEnum[T ~string](block *terraform.Block, key string, def T, va
 func requiredString(block *terraform.Block, key string) (string, *hcl.Diagnostic) {
 	tyAttr := block.GetAttribute(key)
 	tyVal := tyAttr.Value()
+
 	if tyVal.Type() != cty.String {
 		typeName := "<nil>"
 		if !tyVal.Type().Equals(cty.NilType) {
@@ -282,7 +283,6 @@ func requiredString(block *terraform.Block, key string) (string, *hcl.Diagnostic
 
 		if tyAttr.IsNotNil() {
 			diag.Subject = &(tyAttr.HCLAttribute().Range)
-			// diag.Context = &(block.HCLBlock().DefRange)
 			diag.Expression = tyAttr.HCLAttribute().Expr
 		}
 
@@ -297,8 +297,23 @@ func requiredString(block *terraform.Block, key string) (string, *hcl.Diagnostic
 		return "", diag
 	}
 
-	// nolint:gocritic // string type asserted
-	return tyVal.AsString(), nil
+	tyValStr, ok := hclext.AsString(tyVal)
+	if !ok {
+		// Either the val is unknown or null
+		diag := &hcl.Diagnostic{
+			Severity:    hcl.DiagError,
+			Summary:     fmt.Sprintf("Invalid %q attribute for block %s", key, block.Label()),
+			Detail:      "Expected a string, got an unknown or null value",
+			EvalContext: block.Context().Inner(),
+		}
+
+		if tyAttr.IsNotNil() {
+			diag.Subject = &(tyAttr.HCLAttribute().Range)
+			diag.Expression = tyAttr.HCLAttribute().Expr
+		}
+		return "", diag
+	}
+	return tyValStr, nil
 }
 
 func optionalBoolean(block *terraform.Block, key string) bool {

hclext/merge.go

@@ -11,12 +11,12 @@ func MergeObjects(a, b cty.Value) cty.Value {
 		output[key] = val
 	}
 	b.ForEachElement(func(key, val cty.Value) (stop bool) {
-		// TODO: Should this error be captured?
-		if key.Type() != cty.String {
-			return true
-		}
 		//nolint:gocritic // string type asserted above
-		k := key.AsString()
+		k, ok := AsString(key)
+		if !ok {
+			// TODO: Should this error be captured?
+			return stop
+		}
 		old := output[k]
 		if old.IsKnown() && isNotEmptyObject(old) && isNotEmptyObject(val) {
 			output[k] = MergeObjects(old, val)

hclext/references.go

@@ -68,7 +68,12 @@ func CreateDotReferenceFromTraversal(traversals ...hcl.Traversal) string {
 				switch {
 				case part.Key.Type().Equals(cty.String):
 					//nolint:gocritic // string type asserted above
-					refParts = append(refParts, fmt.Sprintf("[%s]", part.Key.AsString()))
+					stringName, ok := AsString(part.Key)
+					if !ok {
+						// Nothing we can do, just put a placeholder
+						stringName = "??"
+					}
+					refParts = append(refParts, fmt.Sprintf("[%s]", stringName))
 				case part.Key.Type().Equals(cty.Number):
 					idx, _ := part.Key.AsBigFloat().Int64()
 					refParts = append(refParts, fmt.Sprintf("[%d]", idx))

init.go

@@ -5,6 +5,8 @@ import (
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/function"
 	"golang.org/x/xerrors"
+
+	"github.com/coder/preview/hclext"
 )
 
 // init intends to override some of the default functions afforded by terraform.
@@ -27,7 +29,11 @@ func init() {
 		Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
 			// This code is taken directly from https://github.com/mitchellh/go-homedir/blob/af06845cf3004701891bf4fdb884bfe4920b3727/homedir.go#L58
 			// The only change is that instead of expanding the path, we return an error
-			path := args[0].AsString()
+			path, ok := hclext.AsString(args[0])
+			if !ok {
+				return cty.NilVal, xerrors.Errorf("invalid path argument")
+			}
+
 			if len(path) == 0 {
 				return cty.StringVal(path), nil
 			}

paramhook.go

@@ -39,8 +39,10 @@ func parameterContextsEvalHook(input Input) func(ctx *tfcontext.Context, blocks
 				continue
 			}
 
-			//nolint:gocritic // string type asserted
-			name := nameVal.AsString()
+			name, ok := hclext.AsString(nameVal)
+			if !ok {
+				continue
+			}
 			var value cty.Value
 			pv, ok := input.RichParameterValue(name)
 			if ok {