Negative get attr s3 tree fix

.changes/next-release/feature-f8f220029d625913ed04f319494ff9fed5cad7d8.json

@@ -0,0 +1,7 @@
+{
+  "type": "feature",
+  "description": "Add support for negative GetAttr indexing",
+  "pull_requests": [
+    "[#2937](https://github.com/smithy-lang/smithy/pull/2937)"
+  ]
+}

docs/source-2.0/additional-specs/rules-engine/standard-library.rst

@@ -116,6 +116,10 @@ parsed value of the ``foo`` parameter:
         ]
     }
 
+.. note::
+
+    Negative array indexing is available since 1.1.
+
 
 .. _rules-engine-standard-library-getAttr-path-strings:
 
@@ -126,7 +130,9 @@ Parsing ``path`` strings
 Path strings for the `getAttr function`_ are composed of two components:
 
 #. Keys, e.g. ``scheme`` in ``uri#scheme``.
-#. Indexes, e.g. ``[2]`` in ``list[2]``.
+#. Indexes, e.g. ``[2]`` in ``list[2]``. Negative indexes are supported,
+   where ``[-1]`` returns the last element, ``[-2]`` returns the second-to-last,
+   and so on.
 
 An index MUST only occur at the end of a path, as indexes always return
 ``option`` values.

smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/s3/S3AzCanonicalizerTransform.java

@@ -77,13 +77,13 @@ private static boolean isAzIdSubstringBinding(Condition cond) {
         return target instanceof Reference && ID_BUCKET.equals(((Reference) target).getName());
     }
 
-    // Creates: s3expressAvailabilityZoneId = split(Bucket, "--", 0)[1]
+    // Creates: s3expressAvailabilityZoneId = split(Bucket, "--", 0)[-2]
     private static Condition createCanonicalAzCondition(Condition original) {
         Split split = Split.ofExpressions(
                 Expression.getReference(ID_BUCKET),
                 Expression.of("--"),
                 Expression.of(0));
-        GetAttr azExpr = GetAttr.ofExpressions(split, "[1]");
+        GetAttr azExpr = GetAttr.ofExpressions(split, "[-2]");
         return original.toBuilder().fn(azExpr).build();
     }
 }

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/functions/GetAttr.java

@@ -14,12 +14,14 @@
 import software.amazon.smithy.model.node.Node;
 import software.amazon.smithy.model.node.ObjectNode;
 import software.amazon.smithy.model.node.StringNode;
+import software.amazon.smithy.rulesengine.language.RulesVersion;
 import software.amazon.smithy.rulesengine.language.error.InnerParseError;
 import software.amazon.smithy.rulesengine.language.error.InvalidRulesException;
 import software.amazon.smithy.rulesengine.language.evaluation.Scope;
 import software.amazon.smithy.rulesengine.language.evaluation.type.ArrayType;
 import software.amazon.smithy.rulesengine.language.evaluation.type.RecordType;
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
+import software.amazon.smithy.rulesengine.language.evaluation.value.ArrayValue;
 import software.amazon.smithy.rulesengine.language.evaluation.value.Value;
 import software.amazon.smithy.rulesengine.language.syntax.Identifier;
 import software.amazon.smithy.rulesengine.language.syntax.ToExpression;
@@ -79,6 +81,21 @@ public static GetAttr ofExpressions(ToExpression arg1, String arg2) {
         return ofExpressions(arg1, Expression.of(arg2));
     }
 
+    @Override
+    public RulesVersion availableSince() {
+        // Negative index only available since 1.1.
+        for (Part part : path) {
+            if (part instanceof Part.Index) {
+                Part.Index index = (Part.Index) part;
+                if (index.index < 0) {
+                    return RulesVersion.V1_1;
+                }
+            }
+        }
+
+        return RulesVersion.V1_0;
+    }
+
     /**
      * Parses the path argument to getAttr.
      *
@@ -100,10 +117,6 @@ private static List<Part> parse(String path, FromSourceLocation sourceLocation)
                 try {
                     String number = slicePart.substring(1, slicePart.length() - 1);
                     int slice = Integer.parseInt(number);
-                    if (slice < 0) {
-                        throw new InvalidRulesException("Invalid path component: slice index must be >= 0",
-                                sourceLocation);
-                    }
                     if (slicePartIndex > 0) {
                         result.add(Part.Key.of(component.substring(0, slicePartIndex)));
                     }
@@ -316,7 +329,8 @@ public Type typeCheck(Type container) throws InnerParseError {
 
             @Override
             public Value eval(Value container) {
-                return container.expectArrayValue().get(index);
+                ArrayValue values = container.expectArrayValue();
+                return index >= 0 ? values.get(index) : values.get(values.getValues().size() + index);
             }
 
             public int index() {

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/invalid/get-attr-not-1.0.errors

@@ -0,0 +1,5 @@
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#endpointRuleSet | UnstableTrait.smithy.rules#endpointRuleSet
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#endpointTests | UnstableTrait.smithy.rules#endpointTests
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#clientContextParams | UnstableTrait.smithy.rules#clientContextParams
+[ERROR] example#TestService: GetAttr requires rules engine version >= 1.1, but ruleset declares version 1.0 | RulesEngineVersion
+[ERROR] example#TestService: Split requires rules engine version >= 1.1, but ruleset declares version 1.0 | RulesEngineVersion

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/invalid/get-attr-not-1.0.smithy

@@ -0,0 +1,66 @@
+$version: "2.0"
+
+namespace example
+
+use smithy.rules#clientContextParams
+use smithy.rules#endpointRuleSet
+use smithy.rules#endpointTests
+
+@endpointRuleSet({
+    "version": "1.0", // this will fail because negative getAttr requires 1.1
+    "parameters": {
+        "Input": {
+            "type": "string",
+            "required": true,
+            "documentation": "The input string to split"
+        }
+    },
+    "rules": [
+        {
+            "documentation": "Test negative index access",
+            "conditions": [
+                {
+                    "fn": "split",
+                    "argv": ["{Input}", "--", 0],
+                    "assign": "parts"
+                },
+                {
+                    "fn": "getAttr",
+                    "argv": [{"ref": "parts"}, "[-1]"],
+                    "assign": "last"
+                },
+                {
+                    "fn": "getAttr",
+                    "argv": [{"ref": "parts"}, "[-2]"],
+                    "assign": "secondLast"
+                }
+            ],
+            "endpoint": {
+                "url": "https://example.com/{secondLast}/{last}"
+            },
+            "type": "endpoint"
+        },
+        {
+            "documentation": "Fallback",
+            "conditions": [],
+            "error": "No input provided",
+            "type": "error"
+        }
+    ]
+})
+@endpointTests({
+    "version": "1.0",
+    "testCases": [
+        {
+            "documentation": "S3Express bucket with multiple delimiters extracts AZ correctly",
+            "params": {"Input": "my--s3--bucket--abcd-ab1--x-s3"},
+            "expect": {
+                "endpoint": {"url": "https://example.com/abcd-ab1/x-s3"}
+            }
+        }
+    ]
+})
+@clientContextParams(
+    Input: {type: "string", documentation: "The input string"}
+)
+service TestService {}

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/deprecated-param.smithy

@@ -36,7 +36,7 @@ use smithy.rules#endpointRuleSet
       "type": "endpoint"
     }
   ],
-  "version": "1.3"
+  "version": "1.1"
 })
 @clientContextParams(
   Region: {type: "string", documentation: "docs"}

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/duplicate-param.smithy

@@ -7,7 +7,7 @@ use smithy.rules#endpointRuleSet
 use smithy.rules#staticContextParams
 
 @endpointRuleSet({
-    "version": "1.3",
+    "version": "1.1",
     "parameters": {
         "ParameterBar": {
             "type": "String",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/get-attr-negative-index.errors

@@ -0,0 +1,3 @@
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#endpointRuleSet | UnstableTrait
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#endpointTests | UnstableTrait
+[WARNING] example#TestService: This shape applies a trait that is unstable: smithy.rules#clientContextParams | UnstableTrait

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/get-attr-negative-index.smithy

@@ -0,0 +1,73 @@
+$version: "2.0"
+
+namespace example
+
+use smithy.rules#clientContextParams
+use smithy.rules#endpointRuleSet
+use smithy.rules#endpointTests
+
+@endpointRuleSet({
+    "version": "1.1",
+    "parameters": {
+        "Input": {
+            "type": "string",
+            "required": true,
+            "documentation": "The input string to split"
+        }
+    },
+    "rules": [
+        {
+            "documentation": "Test negative index access",
+            "conditions": [
+                {
+                    "fn": "split",
+                    "argv": ["{Input}", "--", 0],
+                    "assign": "parts"
+                },
+                {
+                    "fn": "getAttr",
+                    "argv": [{"ref": "parts"}, "[-1]"],
+                    "assign": "last"
+                },
+                {
+                    "fn": "getAttr",
+                    "argv": [{"ref": "parts"}, "[-2]"],
+                    "assign": "secondLast"
+                }
+            ],
+            "endpoint": {
+                "url": "https://example.com/{secondLast}/{last}"
+            },
+            "type": "endpoint"
+        },
+        {
+            "documentation": "Fallback",
+            "conditions": [],
+            "error": "No input provided",
+            "type": "error"
+        }
+    ]
+})
+@endpointTests({
+    "version": "1.0",
+    "testCases": [
+        {
+            "documentation": "S3Express bucket with multiple delimiters extracts AZ correctly",
+            "params": {"Input": "my--s3--bucket--abcd-ab1--x-s3"},
+            "expect": {
+                "endpoint": {"url": "https://example.com/abcd-ab1/x-s3"}
+            }
+        },
+        {
+            "documentation": "Simple two-part split",
+            "params": {"Input": "first--second"},
+            "expect": {
+                "endpoint": {"url": "https://example.com/first/second"}
+            }
+        }
+    ]
+})
+@clientContextParams(
+    Input: {type: "string", documentation: "The input string"}
+)
+service TestService {}

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/get-attr-type-inference.smithy

@@ -6,7 +6,7 @@ use smithy.rules#clientContextParams
 use smithy.rules#endpointRuleSet
 
 @endpointRuleSet({
-  "version": "1.3",
+  "version": "1.1",
   "parameters": {
     "Bucket": {
       "type": "string",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/headers.smithy

@@ -47,7 +47,7 @@ use smithy.rules#endpointTests
       "type": "error"
     }
   ],
-  "version": "1.3"
+  "version": "1.1"
 })
 @endpointTests(
   "version": "1.0",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/minimal-ruleset.smithy

@@ -6,7 +6,7 @@ use smithy.rules#clientContextParams
 use smithy.rules#endpointRuleSet
 
 @endpointRuleSet({
-  "version": "1.3",
+  "version": "1.1",
   "parameters": {
     "Region": {
       "required": true,

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/parse-url.smithy

@@ -7,7 +7,7 @@ use smithy.rules#endpointRuleSet
 use smithy.rules#endpointTests
 
 @endpointRuleSet({
-  "version": "1.3",
+  "version": "1.1",
   "parameters": {
     "Endpoint": {
       "type": "string",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/split.smithy

@@ -7,7 +7,7 @@ use smithy.rules#endpointRuleSet
 use smithy.rules#endpointTests
 
 @endpointRuleSet({
-    "version": "1.3",
+    "version": "1.1",
     "parameters": {
         "Input": {
             "type": "string",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/substring.smithy

@@ -99,7 +99,7 @@ use smithy.rules#endpointTests
       "type": "error"
     }
   ],
-  "version": "1.3"
+  "version": "1.1"
 })
 @endpointTests(
   version: "1.0",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/uri-encode.smithy

@@ -7,7 +7,7 @@ use smithy.rules#endpointRuleSet
 use smithy.rules#endpointTests
 
 @endpointRuleSet({
-  "version": "1.3",
+  "version": "1.1",
   "parameters": {
     "TestCaseId": {
       "type": "string",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/valid-hostlabel.smithy

@@ -58,7 +58,7 @@ use smithy.rules#endpointTests
       "type": "error"
     }
   ],
-  "version": "1.3"
+  "version": "1.1"
 })
 @endpointTests(
   version: "1.0",

smithy-rules-engine/src/test/resources/software/amazon/smithy/rulesengine/language/errorfiles/valid/valid-model.smithy

@@ -8,7 +8,7 @@ use smithy.rules#endpointRuleSet
 use smithy.rules#staticContextParams
 
 @endpointRuleSet({
-    "version": "1.3",
+    "version": "1.1",
     "parameters": {
         "Region": {
             "type": "string",