bugfix(cliconfig.go): emit a warning msg if bad CLI config file path

internal/command/cliconfig/cliconfig.go

@@ -9,7 +9,9 @@
 package cliconfig
 
 import (
+	"errors"
 	"fmt"
+	"io/fs"
 	"io/ioutil"
 	"log"
 	"os"
@@ -102,12 +104,14 @@ func LoadConfig() (*Config, tfdiags.Diagnostics) {
 	configVal := BuiltinConfig // copy
 	config := &configVal
 
-	if mainFilename, err := cliConfigFile(); err == nil {
+	if mainFilename, mainFileDiags := cliConfigFile(); len(mainFileDiags) == 0 {
 		if _, err := os.Stat(mainFilename); err == nil {
 			mainConfig, mainDiags := loadConfigFile(mainFilename)
 			diags = diags.Append(mainDiags)
 			config = config.Merge(mainConfig)
 		}
+	} else {
+		diags = diags.Append(mainFileDiags)
 	}
 
 	// Unless the user has specifically overridden the configuration file
@@ -407,7 +411,8 @@ func (c *Config) Merge(c2 *Config) *Config {
 	return &result
 }
 
-func cliConfigFile() (string, error) {
+func cliConfigFile() (string, tfdiags.Diagnostics) {
+	var diags tfdiags.Diagnostics
 	mustExist := true
 
 	configFilePath := cliConfigFileOverride()
@@ -427,15 +432,19 @@ func cliConfigFile() (string, error) {
 	f, err := os.Open(configFilePath)
 	if err == nil {
 		f.Close()
-		return configFilePath, nil
+		return configFilePath, diags
 	}
 
-	if mustExist || !os.IsNotExist(err) {
-		return "", err
+	if mustExist || !errors.Is(err, fs.ErrNotExist) {
+		diags = append(diags, tfdiags.Sourceless(
+			tfdiags.Warning,
+			"Unable to open CLI configuration file",
+			fmt.Sprintf("The CLI configuration file at %q does not exist.", configFilePath),
+		))
 	}
 
 	log.Println("[DEBUG] File doesn't exist, but doesn't need to. Ignoring.")
-	return "", nil
+	return "", diags
 }
 
 func cliConfigFileOverride() string {

internal/command/cliconfig/cliconfig_test.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/davecgh/go-spew/spew"
 	"github.com/google/go-cmp/cmp"
+	"github.com/hashicorp/terraform/internal/tfdiags"
 )
 
 // This is the directory where our test fixtures are.
@@ -55,6 +56,31 @@ func TestLoadConfig_envSubst(t *testing.T) {
 	}
 }
 
+func TestLoadConfig_non_existing_file(t *testing.T) {
+	tmpDir := os.TempDir()
+	cliTmpFile := filepath.Join(tmpDir, "dev.tfrc")
+
+	os.Setenv("TF_CLI_CONFIG_FILE", cliTmpFile)
+	defer os.Unsetenv("TF_CLI_CONFIG_FILE")
+
+	c, errs := LoadConfig()
+	if errs.HasErrors() || c.Validate().HasErrors() {
+		t.Fatalf("err: %s", errs)
+	}
+
+	hasOpenFileWarn := false
+	for _, err := range errs {
+		if err.Severity() == tfdiags.Warning && err.Description().Summary == "Unable to open CLI configuration file" {
+			hasOpenFileWarn = true
+			break
+		}
+	}
+
+	if !hasOpenFileWarn {
+		t.Fatal("expecting a warning message because of nonexisting CLI configuration file")
+	}
+}
+
 func TestEnvConfig(t *testing.T) {
 	tests := map[string]struct {
 		env  map[string]string