From 78025b1bcabcba12fa4b4bcde2761655c43f509c Mon Sep 17 00:00:00 2001
From: Radek Simko <radek.simko@gmail.com>
Date: Thu, 24 Sep 2020 19:46:39 +0100
Subject: [PATCH 1/3] fmt: Gate formatting command on 0.7.7

---
 tfexec/errors.go   | 10 ++++++++++
 tfexec/fmt.go      |  5 +++++
 tfexec/fmt_test.go | 37 +++++++++++++++++++++++++++++++++++++
 tfexec/version.go  |  1 +
 4 files changed, 53 insertions(+)
 create mode 100644 tfexec/fmt_test.go

diff --git a/tfexec/errors.go b/tfexec/errors.go
index 010b3887..e7a6c804 100644
--- a/tfexec/errors.go
+++ b/tfexec/errors.go
@@ -129,6 +129,16 @@ func (e *ErrVersionMismatch) Error() string {
 	return fmt.Sprintf("unexpected version %s (min: %s, max: %s)", e.Actual, e.MinInclusive, e.MaxExclusive)
 }
 
+func (e *ErrVersionMismatch) Is(target error) bool {
+	err, ok := target.(*ErrVersionMismatch)
+	if !ok {
+		return false
+	}
+	return err.Actual == e.Actual &&
+		err.MaxExclusive == e.MaxExclusive &&
+		err.MinInclusive == e.MinInclusive
+}
+
 type ErrNoInit struct {
 	stderr string
 }
diff --git a/tfexec/fmt.go b/tfexec/fmt.go
index 64473a5e..d80a39b7 100644
--- a/tfexec/fmt.go
+++ b/tfexec/fmt.go
@@ -121,6 +121,11 @@ func (tf *Terraform) FormatCheck(ctx context.Context, opts ...FormatOption) (boo
 }
 
 func (tf *Terraform) formatCmd(ctx context.Context, args []string, opts ...FormatOption) (*exec.Cmd, error) {
+	err := tf.compatible(ctx, tf0_7_7, nil)
+	if err != nil {
+		return nil, fmt.Errorf("fmt was first introduced in Terraform 0.7.7: %w", err)
+	}
+
 	c := defaultFormatConfig
 
 	for _, o := range opts {
diff --git a/tfexec/fmt_test.go b/tfexec/fmt_test.go
new file mode 100644
index 00000000..932c0f09
--- /dev/null
+++ b/tfexec/fmt_test.go
@@ -0,0 +1,37 @@
+package tfexec
+
+import (
+	"context"
+	"errors"
+	"os"
+	"testing"
+)
+
+func TestFormat(t *testing.T) {
+	td := testTempDir(t)
+	defer os.RemoveAll(td)
+
+	tf, err := NewTerraform(td, tfVersion(t, "0.7.6"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// empty env, to avoid environ mismatch in testing
+	tf.SetEnv(map[string]string{})
+
+	t.Run("too old version", func(t *testing.T) {
+		_, err := tf.formatCmd(context.Background(), []string{})
+		if err == nil {
+			t.Fatal("expected old version to fail")
+		}
+
+		expectedErr := &ErrVersionMismatch{
+			Actual:       "0.7.6",
+			MinInclusive: "0.7.7",
+			MaxExclusive: "-",
+		}
+		if !errors.Is(err, expectedErr) {
+			t.Fatalf("error doesn't match: %#v", err)
+		}
+	})
+}
diff --git a/tfexec/version.go b/tfexec/version.go
index ae1dd5fa..6f3f1395 100644
--- a/tfexec/version.go
+++ b/tfexec/version.go
@@ -12,6 +12,7 @@ import (
 )
 
 var (
+	tf0_7_7  = version.Must(version.NewVersion("0.7.7"))
 	tf0_12_0 = version.Must(version.NewVersion("0.12.0"))
 	tf0_13_0 = version.Must(version.NewVersion("0.13.0"))
 )

From 5f1461e1232e6f8a612e702d3cee8070293a46ee Mon Sep 17 00:00:00 2001
From: Radek Simko <radek.simko@gmail.com>
Date: Fri, 25 Sep 2020 10:25:22 +0100
Subject: [PATCH 2/3] avoid error field checking

---
 tfexec/errors.go | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/tfexec/errors.go b/tfexec/errors.go
index e7a6c804..75e62ae1 100644
--- a/tfexec/errors.go
+++ b/tfexec/errors.go
@@ -130,13 +130,8 @@ func (e *ErrVersionMismatch) Error() string {
 }
 
 func (e *ErrVersionMismatch) Is(target error) bool {
-	err, ok := target.(*ErrVersionMismatch)
-	if !ok {
-		return false
-	}
-	return err.Actual == e.Actual &&
-		err.MaxExclusive == e.MaxExclusive &&
-		err.MinInclusive == e.MinInclusive
+	_, ok := target.(*ErrVersionMismatch)
+	return ok
 }
 
 type ErrNoInit struct {

From 1792c628d5a4ee1f88a51cfe385b1e64ec117e40 Mon Sep 17 00:00:00 2001
From: Radek Simko <radek.simko@gmail.com>
Date: Fri, 25 Sep 2020 14:49:41 +0100
Subject: [PATCH 3/3] replace errors.Is with errors.As

---
 tfexec/errors.go   | 5 -----
 tfexec/fmt_test.go | 8 ++------
 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/tfexec/errors.go b/tfexec/errors.go
index 75e62ae1..010b3887 100644
--- a/tfexec/errors.go
+++ b/tfexec/errors.go
@@ -129,11 +129,6 @@ func (e *ErrVersionMismatch) Error() string {
 	return fmt.Sprintf("unexpected version %s (min: %s, max: %s)", e.Actual, e.MinInclusive, e.MaxExclusive)
 }
 
-func (e *ErrVersionMismatch) Is(target error) bool {
-	_, ok := target.(*ErrVersionMismatch)
-	return ok
-}
-
 type ErrNoInit struct {
 	stderr string
 }
diff --git a/tfexec/fmt_test.go b/tfexec/fmt_test.go
index 932c0f09..517c2d04 100644
--- a/tfexec/fmt_test.go
+++ b/tfexec/fmt_test.go
@@ -25,12 +25,8 @@ func TestFormat(t *testing.T) {
 			t.Fatal("expected old version to fail")
 		}
 
-		expectedErr := &ErrVersionMismatch{
-			Actual:       "0.7.6",
-			MinInclusive: "0.7.7",
-			MaxExclusive: "-",
-		}
-		if !errors.Is(err, expectedErr) {
+		var expectedErr *ErrVersionMismatch
+		if !errors.As(err, &expectedErr) {
 			t.Fatalf("error doesn't match: %#v", err)
 		}
 	})