Add import shadowing rule (#76)

Taken from OPA strict mode - we should have it too

Signed-off-by: Anders Eknert <anders@styra.com>

bundle/regal/ast.rego

@@ -5,6 +5,11 @@ import future.keywords.every
 import future.keywords.if
 import future.keywords.in
 
+policy(snippet) := regal.parse_module("policy.rego", concat("", [
+	"package policy\n\n",
+	snippet,
+]))
+
 # METADATA
 # description: parses provided policy with all future keywords imported. Primarily for testing.
 with_future_keywords(policy) := regal.parse_module("policy.rego", concat("", [

bundle/regal/rules/imports/imports.rego

@@ -7,6 +7,19 @@ import future.keywords.in
 import data.regal.config
 import data.regal.result
 
+_identifiers := [_ident(imported) |
+	some imported in input.imports
+]
+
+# regular import
+_ident(imported) := path[count(path) - 1].value if {
+	not imported.alias
+	path := imported.path.value
+}
+
+# aliased import
+_ident(imported) := imported.alias
+
 # METADATA
 # title: implicit-future-keywords
 # description: Use explicit future keyword imports
@@ -29,7 +42,7 @@ report contains violation if {
 	imported.path.value[1].type == "string"
 	imported.path.value[1].value == "keywords"
 
-	violation := result.fail(rego.metadata.rule(), {"location": imported.path.value[0].location})
+	violation := result.fail(rego.metadata.rule(), result.location(imported.path.value[0]))
 }
 
 # METADATA
@@ -51,7 +64,7 @@ report contains violation if {
 	# count(imported.path.value) == 1
 	# imported.alias
 
-	violation := result.fail(rego.metadata.rule(), {"location": imported.path.value[0].location})
+	violation := result.fail(rego.metadata.rule(), result.location(imported.path.value[0]))
 }
 
 # METADATA
@@ -71,5 +84,23 @@ report contains violation if {
 
 	imported.path.value[0].value == "data"
 
-	violation := result.fail(rego.metadata.rule(), {"location": imported.path.value[0].location})
+	violation := result.fail(rego.metadata.rule(), result.location(imported.path.value[0]))
+}
+
+# METADATA
+# title: import-shadows-import
+# description: Import shadows another import
+# related_resources:
+# - description: documentation
+#   ref: https://docs.styra.com/regal/rules/import-shadows-import
+# custom:
+#   category: imports
+report contains violation if {
+	config.for_rule(rego.metadata.rule()).enabled == true
+
+	some i, identifier in _identifiers
+
+	identifier in array.slice(_identifiers, 0, i)
+
+	violation := result.fail(rego.metadata.rule(), result.location(input.imports[i].path.value[0]))
 }

bundle/regal/rules/imports/imports_test.rego

@@ -15,7 +15,7 @@ test_fail_future_keywords_import_wildcard if {
 			"ref": "https://docs.styra.com/regal/rules/implicit-future-keywords",
 		}],
 		"title": "implicit-future-keywords",
-		"location": {"col": 8, "file": "policy.rego", "row": 8},
+		"location": {"col": 8, "file": "policy.rego", "row": 3},
 	}}
 }
 
@@ -40,7 +40,7 @@ test_fail_import_input if {
 			"ref": "https://docs.styra.com/regal/rules/avoid-importing-input",
 		}],
 		"title": "avoid-importing-input",
-		"location": {"col": 8, "file": "policy.rego", "row": 8},
+		"location": {"col": 8, "file": "policy.rego", "row": 3},
 	}}
 }
 
@@ -53,7 +53,7 @@ test_fail_import_data if {
 			"ref": "https://docs.styra.com/regal/rules/redundant-data-import",
 		}],
 		"title": "redundant-data-import",
-		"location": {"col": 8, "file": "policy.rego", "row": 8},
+		"location": {"col": 8, "file": "policy.rego", "row": 3},
 	}}
 }
 
@@ -66,16 +66,48 @@ test_fail_import_data_aliased if {
 			"ref": "https://docs.styra.com/regal/rules/redundant-data-import",
 		}],
 		"title": "redundant-data-import",
-		"location": {"col": 8, "file": "policy.rego", "row": 8},
+		"location": {"col": 8, "file": "policy.rego", "row": 3},
 	}}
 }
 
 test_success_import_data_path if {
 	report(`import data.something`) == set()
 }
 
+test_fail_duplicate_import if {
+	report(`
+	import data.foo
+	import data.foo
+	`) == {{
+		"category": "imports",
+		"description": "Import shadows another import",
+		"related_resources": [{
+			"description": "documentation",
+			"ref": "https://docs.styra.com/regal/rules/import-shadows-import",
+		}],
+		"title": "import-shadows-import",
+		"location": {"col": 9, "file": "policy.rego", "row": 5},
+	}}
+}
+
+test_fail_duplicate_import_alias if {
+	report(`
+	import data.foo
+	import data.bar as foo
+	`) == {{
+		"category": "imports",
+		"description": "Import shadows another import",
+		"related_resources": [{
+			"description": "documentation",
+			"ref": "https://docs.styra.com/regal/rules/import-shadows-import",
+		}],
+		"title": "import-shadows-import",
+		"location": {"col": 9, "file": "policy.rego", "row": 5},
+	}}
+}
+
 report(snippet) := report if {
 	# regal ignore:input-or-data-reference
-	report := imports.report with input as ast.with_future_keywords(snippet)
+	report := imports.report with input as ast.policy(snippet)
 		with config.for_rule as {"enabled": true}
 }