Add rules to enforce snake_case names

docs/rules/README.md

@@ -76,4 +76,5 @@ These rules suggest to better ways.
 |[terraform_documented_variables](terraform_documented_variables.md)||
 |[terraform_typed_variables](terraform_typed_variables.md)||
 |[terraform_module_pinned_source](terraform_module_pinned_source.md)|✔|
+|[terraform_naming_convention](terraform_naming_convention.md)||
 |[terraform_required_version](terraform_required_version.md)||

docs/rules/terraform_naming_convention.md

@@ -0,0 +1,237 @@
+# terraform_naming_convention
+
+Enforces naming conventions for the following blocks:
+
+* Resources
+* Input variables
+* Output values
+* Local values
+* Modules
+* Data sources
+
+## Configuration
+
+Name | Default | Value
+--- | --- | ---
+enabled | `false` | Boolean
+format | `snake_case` | `snake_case`, `mixed_snake_case`, `""`
+custom | `""` | String representation of a golang regular expression that the block name must match
+data | | Block settings to override naming convention for data sources
+locals | | Block settings to override naming convention for local values
+module | | Block settings to override naming convention for modules
+output | | Block settings to override naming convention for output values
+resource | | Block settings to override naming convention for resources
+variable | | Block settings to override naming convention for input variables
+
+
+#### `format`
+
+The `format` option defines the allowed formats for the block label. 
+This option accepts one of the following values:
+
+* `snake_case` - standard snake_case format - all characters must be lower-case, and underscores are allowed.
+* `mixed_snake_case` - modified snake_case format - characters may be upper or lower case, and underscores are allowed.
+* `none` - signifies "this block shall not have its format checked". This can be useful if you want to enforce no particular format for a block.
+
+#### `custom`
+
+The `custom` option defines a custom regex that the identifier must match. This option allows you to have a 
+bit more finer-grained control over identifiers, letting you force certain patterns and substrings.
+
+## Examples
+
+### Default - enforce snake_case for all blocks
+
+#### Rule configuration
+
+```
+rule "terraform_naming_convention" {
+  enabled = true
+}
+```
+
+#### Sample terraform source file
+
+```hcl
+data "aws_eip" "camelCase" {
+}
+
+data "aws_eip" "valid_name" {
+}
+```
+
+```
+$ tflint
+1 issue(s) found:
+
+Notice: data name `camelCase` must match the following format: snake_case (terraform_naming_convention)
+
+  on template.tf line 1:
+   1: data "aws_eip" "camelCase" {
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.15.3/docs/rules/terraform_naming_convention.md
+
+```
+
+
+### Custom naming expression for all blocks
+
+#### Rule configuration
+
+```
+rule "terraform_naming_convention" {
+  enabled = true
+
+  custom = "^[a-zA-Z]+([_-][a-zA-Z]+)*$"
+}
+```
+
+#### Sample terraform source file
+
+```hcl
+resource "aws_eip" "Invalid_Name_With_Number123" {
+}
+
+resource "aws_eip" "Name-With_Dash" {
+}
+```
+
+```
+$ tflint
+1 issue(s) found:
+
+Notice: resource name `Invalid_Name_With_Number123` must match the following RegExp: ^[a-zA-Z]+([_-][a-zA-Z]+)*$ (terraform_naming_convention)
+
+  on template.tf line 1:
+   1: resource "aws_eip" "Invalid_Name_With_Number123" {
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.15.3/docs/rules/terraform_naming_convention.md
+
+```
+
+
+### Override default setting for specific block type
+
+#### Rule configuration
+
+```
+rule "terraform_naming_convention" {
+  enabled = true
+
+  module {
+    custom = "^[a-zA-Z]+(_[a-zA-Z]+)*$"
+  }
+}
+```
+
+#### Sample terraform source file
+
+```hcl
+// data name enforced with default snake_case
+data "aws_eip" "eip_1a" {
+}
+
+module "valid_module" {
+  source = ""
+}
+
+module "invalid_module_with_number_1a" {
+  source = ""
+}
+```
+
+```
+$ tflint
+1 issue(s) found:
+
+Notice: module name `invalid_module_with_number_1a` must match the following RegExp: ^[a-zA-Z]+(_[a-zA-Z]+)*$ (terraform_naming_convention)
+
+  on template.tf line 9:
+   9: module "invalid_module_with_number_1a" {
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.15.3/docs/rules/terraform_naming_convention.md
+
+```
+
+### Disable for specific block type
+
+#### Rule configuration
+
+```
+rule "terraform_naming_convention" {
+  enabled = true
+
+  module {
+    format = "none"
+  }
+}
+```
+
+#### Sample terraform source file
+
+```hcl
+// data name enforced with default snake_case
+data "aws_eip" "eip_1a" {
+}
+
+// module names will not be enforced
+module "Valid_Name-Not-Enforced" {
+  source = ""
+}
+```
+
+
+### Disable for all blocks but enforce a specific block type
+
+#### Rule configuration
+
+```
+rule "terraform_naming_convention" {
+  enabled = true
+  format  = "none"
+
+  local {
+    format = "snake_case"
+  }
+}
+```
+
+#### Sample terraform source file
+
+```hcl
+// Data block name not enforced
+data "aws_eip" "EIP_1a" {
+}
+
+// Resource block name not enforced
+resource "aws_eip" "EIP_1b" {
+}
+
+// local variable names enforced
+locals {
+  valid_name   = "valid"
+  invalid-name = "dashes are not allowed with snake_case"
+}
+```
+
+```
+$ tflint
+1 issue(s) found:
+
+Notice: local value name `invalid-name` must match the following format: snake_case (terraform_naming_convention)
+
+  on template.tf line 12:
+  12: invalid-name = "dashes are not allowed with snake_case"
+
+Reference: https://github.com/terraform-linters/tflint/blob/v0.15.3/docs/rules/terraform_naming_convention.md
+
+```
+
+## Why
+
+Naming conventions are optional, so it is not necessary to follow this. 
+But this rule is useful if you want to force the following naming conventions in line with the [Terraform Plugin Naming Best Practices](https://www.terraform.io/docs/extend/best-practices/naming.html).
+
+## How To Fix
+
+Update the block label according to the format or custom regular expression.

rules/provider.go

@@ -45,6 +45,7 @@ var manualDefaultRules = []Rule{
 	terraformrules.NewTerraformDocumentedOutputsRule(),
 	terraformrules.NewTerraformDocumentedVariablesRule(),
 	terraformrules.NewTerraformModulePinnedSourceRule(),
+	terraformrules.NewTerraformNamingConventionRule(),
 	terraformrules.NewTerraformTypedVariablesRule(),
 	terraformrules.NewTerraformRequiredVersionRule(),
 }