configs: Fix provider requirements panics

When parsing provider requirements we should check the type of the
source and version attributes rather than assuming that they are
strings. Otherwise an invalid attribute value will cause a panic.

configs/provider_requirements.go

@@ -4,6 +4,7 @@ import (
 	version "github.com/hashicorp/go-version"
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/terraform/addrs"
+	"github.com/zclconf/go-cty/cty"
 )
 
 // RequiredProvider represents a declaration of a dependency on a particular
@@ -55,41 +56,61 @@ func decodeRequiredProvidersBlock(block *hcl.Block) (*RequiredProviders, hcl.Dia
 				vc := VersionConstraint{
 					DeclRange: attr.Range,
 				}
-				constraintStr := expr.GetAttr("version").AsString()
-				constraints, err := version.NewConstraint(constraintStr)
-				if err != nil {
-					// NewConstraint doesn't return user-friendly errors, so we'll just
-					// ignore the provided error and produce our own generic one.
+				constraint := expr.GetAttr("version")
+				if !constraint.Type().Equals(cty.String) || constraint.IsNull() {
 					diags = append(diags, &hcl.Diagnostic{
 						Severity: hcl.DiagError,
 						Summary:  "Invalid version constraint",
-						Detail:   "This string does not use correct version constraint syntax.",
+						Detail:   "Version must be specified as a string.",
 						Subject:  attr.Expr.Range().Ptr(),
 					})
 				} else {
-					vc.Required = constraints
-					rp.Requirement = vc
+					constraintStr := constraint.AsString()
+					constraints, err := version.NewConstraint(constraintStr)
+					if err != nil {
+						// NewConstraint doesn't return user-friendly errors, so we'll just
+						// ignore the provided error and produce our own generic one.
+						diags = append(diags, &hcl.Diagnostic{
+							Severity: hcl.DiagError,
+							Summary:  "Invalid version constraint",
+							Detail:   "This string does not use correct version constraint syntax.",
+							Subject:  attr.Expr.Range().Ptr(),
+						})
+					} else {
+						vc.Required = constraints
+						rp.Requirement = vc
+					}
 				}
 			}
 			if expr.Type().HasAttribute("source") {
-				rp.Source = expr.GetAttr("source").AsString()
-
-				fqn, sourceDiags := addrs.ParseProviderSourceString(rp.Source)
-
-				if sourceDiags.HasErrors() {
-					hclDiags := sourceDiags.ToHCL()
-					// The diagnostics from ParseProviderSourceString don't contain
-					// source location information because it has no context to compute
-					// them from, and so we'll add those in quickly here before we
-					// return.
-					for _, diag := range hclDiags {
-						if diag.Subject == nil {
-							diag.Subject = attr.Expr.Range().Ptr()
-						}
-					}
-					diags = append(diags, hclDiags...)
+				source := expr.GetAttr("source")
+				if !source.Type().Equals(cty.String) || source.IsNull() {
+					diags = append(diags, &hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Invalid source",
+						Detail:   "Source must be specified as a string.",
+						Subject:  attr.Expr.Range().Ptr(),
+					})
 				} else {
-					rp.Type = fqn
+					rp.Source = source.AsString()
+
+					fqn, sourceDiags := addrs.ParseProviderSourceString(rp.Source)
+
+					if sourceDiags.HasErrors() {
+						hclDiags := sourceDiags.ToHCL()
+						// The diagnostics from ParseProviderSourceString don't contain
+						// source location information because it has no context to compute
+						// them from, and so we'll add those in quickly here before we
+						// return.
+						for _, diag := range hclDiags {
+							if diag.Subject == nil {
+								diag.Subject = attr.Expr.Range().Ptr()
+							}
+						}
+						diags = append(diags, hclDiags...)
+					} else {
+						rp.Type = fqn
+					}
 				}
 			}
 

configs/provider_requirements_test.go

@@ -306,6 +306,32 @@ func TestDecodeRequiredProvidersBlock(t *testing.T) {
 			},
 			Error: "Invalid required_providers syntax",
 		},
+		"invalid source attribute type": {
+			Block: &hcl.Block{
+				Type: "required_providers",
+				Body: hcltest.MockBody(&hcl.BodyContent{
+					Attributes: hcl.Attributes{
+						"my-test": {
+							Name: "my-test",
+							Expr: hcltest.MockExprLiteral(cty.ObjectVal(map[string]cty.Value{
+								"source": cty.DynamicVal,
+							})),
+						},
+					},
+				}),
+				DefRange: blockRange,
+			},
+			Want: &RequiredProviders{
+				RequiredProviders: map[string]*RequiredProvider{
+					"my-test": {
+						Name:      "my-test",
+						DeclRange: mockRange,
+					},
+				},
+				DeclRange: blockRange,
+			},
+			Error: "Invalid source",
+		},
 	}
 
 	for name, test := range tests {