terraform_required_providers: warn on provider.version

docs/rules/terraform_required_providers.md

@@ -10,7 +10,7 @@ rule "terraform_required_providers" {
 }
 ```
 
-## Example
+## Examples
 
 ```hcl
 provider "template" {}
@@ -20,9 +20,39 @@ provider "template" {}
 $ tflint
 1 issue(s) found:
 
-Warning: Provider "template" should have a version constraint in required_providers
+Warning: Missing version constraint for provider "template" in "required_providers" (terraform_required_providers)
 
-Reference: https://github.com/terraform-linters/tflint/blob/v0.11.0/docs/rules/terraform_required_providers.md 
+  on main.tf line 1:
+   1: provider "template" {}
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.18.0/docs/rules/terraform_required_providers.md
+```
+
+<hr>
+
+```hcl
+provider "template" {
+  version = "2"
+}
+```
+
+```
+$ tflint
+2 issue(s) found:
+
+Warning: provider.template: version constraint should be specified via "required_providers" (terraform_required_providers)
+
+  on main.tf line 1:
+   1: provider "template" {
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.18.0/docs/rules/terraform_required_providers.md
+
+Warning: Missing version constraint for provider "template" in "required_providers" (terraform_required_providers)
+
+  on main.tf line 1:
+   1: provider "template" {
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.18.0/docs/rules/terraform_required_providers.md
 ```
 
 ## Why
@@ -31,7 +61,7 @@ Providers are plugins released on a separate rhythm from Terraform itself, and s
 
 ## How To Fix
 
-Add the `required_providers` attribute to the `terraform` configuration block and include current versions for all providers. For example:
+Add the [`required_providers`](https://www.terraform.io/docs/configuration/terraform.html#specifying-required-provider-versions) block to the `terraform` configuration block and include current versions for all providers. For example:
 
 ```tf
 terraform {
@@ -41,4 +71,4 @@ terraform {
 }
 ```
 
-Provider version constraints can also be specified using a version argument within a provider block but this is not recommend, particularly for child modules.
+Provider version constraints can be specified using a [version argument within a provider block](https://www.terraform.io/docs/configuration/providers.html#provider-versions) for backwards compatability. This approach is now discouraged, particularly for child modules.

rules/terraformrules/terraform_required_providers.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 
+	"github.com/hashicorp/hcl/v2"
 	"github.com/terraform-linters/tflint/tflint"
 )
 
@@ -39,14 +40,26 @@ func (r *TerraformRequiredProvidersRule) Link() string {
 func (r *TerraformRequiredProvidersRule) Check(runner *tflint.Runner) error {
 	log.Printf("[TRACE] Check `%s` rule for `%s` runner", r.Name(), runner.TFConfigPath())
 
+	providers := make(map[string]hcl.Range)
 	module := runner.TFConfig.Module
+
 	for _, provider := range module.ProviderConfigs {
-		if _, ok := module.ProviderRequirements[provider.Name]; !ok && provider.Version.Required == nil {
-			message := fmt.Sprintf(`Provider "%s" should have a version constraint in required_providers`, provider.Name)
-			if provider.Alias != "" {
-				message += fmt.Sprintf(" (%s.%s)", provider.Name, provider.Alias)
-			}
-			runner.EmitIssue(r, message, provider.DeclRange)
+		if _, ok := providers[provider.Name]; !ok {
+			providers[provider.Name] = provider.DeclRange
+		}
+
+		if provider.Version.Required != nil {
+			runner.EmitIssue(
+				r,
+				fmt.Sprintf(`%s: version constraint should be specified via "required_providers"`, provider.Addr().String()),
+				provider.DeclRange,
+			)
+		}
+	}
+
+	for name, decl := range providers {
+		if _, ok := module.ProviderRequirements[name]; !ok {
+			runner.EmitIssue(r, fmt.Sprintf(`Missing version constraint for provider "%s" in "required_providers"`, name), decl)
 		}
 	}
 

rules/terraformrules/terraform_required_providers_test.go

@@ -21,7 +21,7 @@ provider "template" {}
 			Expected: tflint.Issues{
 				{
 					Rule:    NewTerraformRequiredProvidersRule(),
-					Message: `Provider "template" should have a version constraint in required_providers`,
+					Message: `Missing version constraint for provider "template" in "required_providers"`,
 					Range: hcl.Range{
 						Filename: "module.tf",
 						Start: hcl.Pos{
@@ -50,28 +50,55 @@ provider "template" {}
 			Expected: tflint.Issues{},
 		},
 		{
-			Name: "provider alias",
+			Name: "single provider with alias",
 			Content: `
 provider "template" {
-	version = "~> 2"
+	alias = "b"
+}
+`,
+			Expected: tflint.Issues{
+				{
+					Rule:    NewTerraformRequiredProvidersRule(),
+					Message: `Missing version constraint for provider "template" in "required_providers"`,
+					Range: hcl.Range{
+						Filename: "module.tf",
+						Start: hcl.Pos{
+							Line:   2,
+							Column: 1,
+						},
+						End: hcl.Pos{
+							Line:   2,
+							Column: 20,
+						},
+					},
+				},
+			},
+		},
+		{
+			Name: "version set with alias",
+			Content: `
+terraform {
+  required_providers {
+    template = "~> 2"
+  }
 }
 
 provider "template" {
-	alias = "b"
-}
+	version = "~> 2"
+} 
 `,
 			Expected: tflint.Issues{
 				{
 					Rule:    NewTerraformRequiredProvidersRule(),
-					Message: `Provider "template" should have a version constraint in required_providers (template.b)`,
+					Message: `provider.template: version constraint should be specified via "required_providers"`,
 					Range: hcl.Range{
 						Filename: "module.tf",
 						Start: hcl.Pos{
-							Line:   6,
+							Line:   8,
 							Column: 1,
 						},
 						End: hcl.Pos{
-							Line:   6,
+							Line:   8,
 							Column: 20,
 						},
 					},
@@ -81,23 +108,50 @@ provider "template" {
 		{
 			Name: "version set",
 			Content: `
+terraform {
+  required_providers {
+    template = "~> 2"
+  }
+}
+
 provider "template" {
+	alias   = "foo"
 	version = "~> 2"
 } 
 `,
-			Expected: tflint.Issues{},
+			Expected: tflint.Issues{
+				{
+					Rule:    NewTerraformRequiredProvidersRule(),
+					Message: `provider.template.foo: version constraint should be specified via "required_providers"`,
+					Range: hcl.Range{
+						Filename: "module.tf",
+						Start: hcl.Pos{
+							Line:   8,
+							Column: 1,
+						},
+						End: hcl.Pos{
+							Line:   8,
+							Column: 20,
+						},
+					},
+				},
+			},
 		},
 	}
 
 	rule := NewTerraformRequiredProvidersRule()
 
 	for _, tc := range cases {
-		runner := tflint.TestRunner(t, map[string]string{"module.tf": tc.Content})
+		tc := tc
+
+		t.Run(tc.Name, func(t *testing.T) {
+			runner := tflint.TestRunner(t, map[string]string{"module.tf": tc.Content})
 
-		if err := rule.Check(runner); err != nil {
-			t.Fatalf("Unexpected error occurred: %s", err)
-		}
+			if err := rule.Check(runner); err != nil {
+				t.Fatalf("Unexpected error occurred: %s", err)
+			}
 
-		tflint.AssertIssues(t, tc.Expected, runner.Issues)
+			tflint.AssertIssues(t, tc.Expected, runner.Issues)
+		})
 	}
 }