From 01a3376ead589dac1f2a861bef9102bf6fb122b7 Mon Sep 17 00:00:00 2001
From: Alisdair McDiarmid <alisdair@users.noreply.github.com>
Date: Thu, 7 May 2020 14:51:57 -0400
Subject: [PATCH] command: Check required_version before upgrading

If a configuration has a version constraint which prevents use with
Terraform 0.13, the upgrade command should exit before making any
changes.
---
 command/013_config_upgrade.go                 | 22 ++++++++++++++++
 command/013_config_upgrade_test.go            | 26 +++++++++++++++++++
 .../013upgrade-unsupported-version/main.tf    |  1 +
 .../versions.tf                               |  3 +++
 4 files changed, 52 insertions(+)
 create mode 100644 command/testdata/013upgrade-unsupported-version/main.tf
 create mode 100644 command/testdata/013upgrade-unsupported-version/versions.tf

diff --git a/command/013_config_upgrade.go b/command/013_config_upgrade.go
index 850dfa525..b7f0da6be 100644
--- a/command/013_config_upgrade.go
+++ b/command/013_config_upgrade.go
@@ -15,6 +15,7 @@ import (
 	"github.com/hashicorp/terraform/configs"
 	"github.com/hashicorp/terraform/internal/getproviders"
 	"github.com/hashicorp/terraform/tfdiags"
+	tfversion "github.com/hashicorp/terraform/version"
 	"github.com/zclconf/go-cty/cty"
 )
 
@@ -140,6 +141,27 @@ func (c *ZeroThirteenUpgradeCommand) Run(args []string) int {
 		))
 	}
 
+	// Check Terraform required_version constraints
+	for _, file := range files {
+		for _, constraint := range file.CoreVersionConstraints {
+			if !constraint.Required.Check(tfversion.SemVer) {
+				diags = diags.Append(&hcl.Diagnostic{
+					Severity: hcl.DiagError,
+					Summary:  "Unsupported Terraform Core version",
+					Detail: fmt.Sprintf(
+						"This configuration does not support Terraform version %s. To proceed, either choose another supported Terraform version or update this version constraint. Version constraints are normally set for good reason, so updating the constraint may lead to other errors or unexpected behavior.",
+						tfversion.String(),
+					),
+					Subject: &constraint.DeclRange,
+				})
+			}
+		}
+	}
+	if diags.HasErrors() {
+		c.showDiagnostics(diags)
+		return 1
+	}
+
 	// Build up a list of required providers, uniquely by local name
 	requiredProviders := make(map[string]*configs.RequiredProvider)
 	var rewritePaths []string
diff --git a/command/013_config_upgrade_test.go b/command/013_config_upgrade_test.go
index b302cfc4b..b35b464cb 100644
--- a/command/013_config_upgrade_test.go
+++ b/command/013_config_upgrade_test.go
@@ -220,6 +220,32 @@ func TestZeroThirteenUpgrade_skippedFiles(t *testing.T) {
 	}
 }
 
+func TestZeroThirteenUpgrade_unsupportedVersion(t *testing.T) {
+	inputPath := testFixturePath("013upgrade-unsupported-version")
+
+	td := tempDir(t)
+	copy.CopyDir(inputPath, td)
+	defer os.RemoveAll(td)
+	defer testChdir(t, td)()
+
+	ui := new(cli.MockUi)
+	c := &ZeroThirteenUpgradeCommand{
+		Meta: Meta{
+			testingOverrides: metaOverridesForProvider(testProvider()),
+			Ui:               ui,
+		},
+	}
+
+	if code := c.Run(nil); code == 0 {
+		t.Fatal("expected error, got:", ui.OutputWriter)
+	}
+
+	errMsg := ui.ErrorWriter.String()
+	if !strings.Contains(errMsg, `Unsupported Terraform Core version`) {
+		t.Fatal("missing version constraint error:", errMsg)
+	}
+}
+
 func TestZeroThirteenUpgrade_invalidFlags(t *testing.T) {
 	td := tempDir(t)
 	os.MkdirAll(td, 0755)
diff --git a/command/testdata/013upgrade-unsupported-version/main.tf b/command/testdata/013upgrade-unsupported-version/main.tf
new file mode 100644
index 000000000..c7dee23c9
--- /dev/null
+++ b/command/testdata/013upgrade-unsupported-version/main.tf
@@ -0,0 +1 @@
+resource foo_instance a {}
diff --git a/command/testdata/013upgrade-unsupported-version/versions.tf b/command/testdata/013upgrade-unsupported-version/versions.tf
new file mode 100644
index 000000000..7000b050c
--- /dev/null
+++ b/command/testdata/013upgrade-unsupported-version/versions.tf
@@ -0,0 +1,3 @@
+terraform {
+  required_version = "~> 0.12.0"
+}