internal/fwschema: Validate leading numerics in attribute names

.changes/unreleased/ENHANCEMENTS-20230330-105617.yaml

@@ -0,0 +1,6 @@
+kind: ENHANCEMENTS
+body: 'datasource/schema: Raise validation errors if attempting to use attribute names
+  with leading numerics (0-9), which are invalid in the Terraform configuration language'
+time: 2023-03-30T10:56:17.789569-04:00
+custom:
+  Issue: "705"

.changes/unreleased/ENHANCEMENTS-20230330-105618.yaml

@@ -0,0 +1,6 @@
+kind: ENHANCEMENTS
+body: 'provider/schema: Raise validation errors if attempting to use attribute names
+  with leading numerics (0-9), which are invalid in the Terraform configuration language'
+time: 2023-03-30T10:56:18.789569-04:00
+custom:
+  Issue: "705"

.changes/unreleased/ENHANCEMENTS-20230330-105619.yaml

@@ -0,0 +1,6 @@
+kind: ENHANCEMENTS
+body: 'resource/schema: Raise validation errors if attempting to use attribute names
+  with leading numerics (0-9), which are invalid in the Terraform configuration language'
+time: 2023-03-30T10:56:19.789569-04:00
+custom:
+  Issue: "705"

internal/fwschema/attribute_name_validation.go

@@ -3,11 +3,16 @@ package fwschema
 import (
 	"fmt"
 	"regexp"
+	"strings"
 
 	"github.com/hashicorp/terraform-plugin-framework/diag"
 	"github.com/hashicorp/terraform-plugin-framework/path"
 )
 
+// NumericPrefixRegex is a regular expression which matches whether a string
+// begins with a numeric (0-9).
+var NumericPrefixRegex = regexp.MustCompile(`^[0-9]`)
+
 // ReservedProviderAttributeNames contains the list of root attribute names
 // which should not be included in provider-defined provider schemas since
 // they require practitioners to implement special syntax in their
@@ -51,11 +56,8 @@ var ReservedResourceAttributeNames = []string{
 // including them in attribute names. Introducing them could cause practitioner
 // confusion.
 //
-// TODO: Validate leading numeric characters
-// Reference: https://github.com/hashicorp/terraform-plugin-framework/issues/705
-//
 // [identifiers]: https://developer.hashicorp.com/terraform/language/syntax/configuration#identifiers
-var ValidAttributeNameRegex = regexp.MustCompile("^[a-z0-9_]+$")
+var ValidAttributeNameRegex = regexp.MustCompile("^[a-z_][a-z0-9_]*$")
 
 // IsReservedProviderAttributeName returns an error diagnostic if the given
 // attribute path represents a root attribute name in
@@ -134,6 +136,16 @@ func IsValidAttributeName(name string, attributePath path.Path) diag.Diagnostics
 		return diags
 	}
 
+	var message strings.Builder
+
+	message.WriteString("Names must ")
+
+	if NumericPrefixRegex.MatchString(name) {
+		message.WriteString("begin with a lowercase alphabet character (a-z) or underscore (_) and must ")
+	}
+
+	message.WriteString("only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).")
+
 	// The diagnostic path is intentionally omitted as it is invalid in this
 	// context. Diagnostic paths are intended to be mapped to actual data,
 	// while this path information must be synthesized.
@@ -142,7 +154,7 @@ func IsValidAttributeName(name string, attributePath path.Path) diag.Diagnostics
 		"When validating the schema, an implementation issue was found. "+
 			"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
 			fmt.Sprintf("%q at schema path %q is an invalid attribute/block name. ", name, attributePath)+
-			"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+			message.String(),
 	)
 
 	return diags

internal/fwschema/attribute_name_validation_test.go

@@ -217,3 +217,128 @@ func TestIsReservedResourceAttributeName(t *testing.T) {
 		})
 	}
 }
+
+func TestIsValidAttributeName(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		name     string
+		expected diag.Diagnostics
+	}{
+		"empty": {
+			name: "",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"\" at schema path \"\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"ascii-lowercase-alphabet": {
+			name:     "test",
+			expected: nil,
+		},
+		"ascii-lowercase-alphabet-leading-underscore": {
+			name:     "_test",
+			expected: nil,
+		},
+		"ascii-lowercase-alphabet-middle-hyphens": {
+			name: "test-me",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"test-me\" at schema path \"test-me\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"ascii-lowercase-alphabet-middle-underscore": {
+			name:     "test_me",
+			expected: nil,
+		},
+		"ascii-lowercase-alphanumeric": {
+			name:     "test123",
+			expected: nil,
+		},
+		"ascii-lowercase-alphanumeric-leading-numeric": {
+			name: "123test",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"123test\" at schema path \"123test\" is an invalid attribute/block name. "+
+						"Names must begin with a lowercase alphabet character (a-z) or underscore (_) and "+
+						"must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"ascii-uppercase-alphabet": {
+			name: "TEST",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"TEST\" at schema path \"TEST\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"ascii-uppercase-alphanumeric": {
+			name: "TEST123",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"TEST123\" at schema path \"TEST123\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"invalid-bytes": {
+			name: "\xff\xff",
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"\\xff\\xff\" at schema path \"\\xff\\xff\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+		"unicode": {
+			name: `tést`, // t, latin small letter e with acute (00e9), s, t
+			expected: diag.Diagnostics{
+				diag.NewErrorDiagnostic(
+					"Invalid Attribute/Block Name",
+					"When validating the schema, an implementation issue was found. "+
+						"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+						"\"tést\" at schema path \"tést\" is an invalid attribute/block name. "+
+						"Names must only contain lowercase alphanumeric characters (a-z, 0-9) and underscores (_).",
+				),
+			},
+		},
+	}
+
+	for name, testCase := range testCases {
+		name, testCase := name, testCase
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			got := fwschema.IsValidAttributeName(testCase.name, path.Root(testCase.name))
+
+			if diff := cmp.Diff(got, testCase.expected); diff != "" {
+				t.Errorf("unexpected difference: %s", diff)
+			}
+		})
+	}
+}