[wasm][debugger] Indexing with expression (dotnet#75524)

* Support for simple mathematical expressions + tests.

* A bit more complex expressions.

* Applied @radical's suggestions.

* [wasm][debugger] Add another test for EvaluateIndexingByExpressionContainingUnknownIdentifier

* [wasm][debugger] Add a broken case of indexing with string accessor

Co-authored-by: Ankit Jain <radical@gmail.com>

src/mono/wasm/debugger/BrowserDebugProxy/MemberReferenceResolver.cs

@@ -8,6 +8,8 @@
 using Microsoft.Extensions.Logging;
 using Newtonsoft.Json.Linq;
 using System.IO;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using System.Collections.Generic;
 using System.Net.WebSockets;
@@ -406,7 +408,16 @@ public async Task<JObject> Resolve(ElementAccessExpressionSyntax elementAccess,
                                     indexObject ??= await Resolve(argParm.Identifier.Text, token);
                                     elementIdxStr += indexObject["value"].ToString();
                                 }
-                                // FixMe: indexing with expressions, e.g. x[a + 1]
+                                // indexing with expressions, e.g. x[a + 1]
+                                else
+                                {
+                                    string expression = arg.ToString();
+                                    indexObject = await ExpressionEvaluator.EvaluateSimpleExpression(this, expression, expression, variableDefinitions, logger, token);
+                                    string type = indexObject["type"].Value<string>();
+                                    if (type != "number")
+                                        throw new InvalidOperationException($"Cannot index with an object of type '{type}'");
+                                    elementIdxStr += indexObject["value"].ToString();
+                                }
                             }
                         }
                     }

src/mono/wasm/debugger/DebuggerTestSuite/EvaluateOnCallFrameTests.cs

@@ -627,6 +627,61 @@ await EvaluateOnCallFrameAndCheck(id,
 
            });
 
+        [Fact]
+        public async Task EvaluateIndexingByExpression() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.EvaluateLocalsWithIndexingTests", "EvaluateLocals", 5, "DebuggerTests.EvaluateLocalsWithIndexingTests.EvaluateLocals",
+            "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.EvaluateLocalsWithIndexingTests:EvaluateLocals'); })",
+            wait_for_event_fn: async (pause_location) =>
+            {
+                var id = pause_location["callFrames"][0]["callFrameId"].Value<string>();
+                await EvaluateOnCallFrameAndCheck(id,
+                    ("f.numList[i + 1]", TNumber(2)),
+                    ("f.textList[(2 * j) - 1]", TString("2")),
+                    ("f.textList[j - 1]", TString("1")),
+                    //("f[\"longstring\"]", TBool(true)), FIXME: Broken case
+                    ("f.numArray[f.numList[j - 1]]", TNumber(2))
+                );
+            });
+
+        [Fact]
+        public async Task EvaluateIndexingByExpressionMultidimensional() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.EvaluateLocalsWithMultidimensionalIndexingTests", "EvaluateLocals", 5, "DebuggerTests.EvaluateLocalsWithMultidimensionalIndexingTests.EvaluateLocals",
+            "window.setTimeout(function() { invoke_static_method ('[debugger-test] DebuggerTests.EvaluateLocalsWithMultidimensionalIndexingTests:EvaluateLocals'); })",
+            wait_for_event_fn: async (pause_location) =>
+            {
+                var id = pause_location["callFrames"][0]["callFrameId"].Value<string>();
+                await EvaluateOnCallFrameAndCheck(id,
+                    ("f.numArray2D[0, j - 1]", TNumber(1)), // 0, 0
+                    ("f.numArray2D[f.idx1, i + j]", TNumber(4)), // 1, 1
+                    ("f.numArray2D[(f.idx1 - j) * 5, i + j]", TNumber(2)), // 0, 1
+                    ("f.numArray2D[i + j, f.idx1 - 1]", TNumber(3)) // 1, 0
+                );
+            });
+
+        [ConditionalFact(nameof(RunningOnChrome))]
+        public async Task EvaluateIndexingByExpressionNegative() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.EvaluateLocalsWithIndexingTests", "EvaluateLocals", 5, "DebuggerTests.EvaluateLocalsWithIndexingTests.EvaluateLocals",
+            $"window.setTimeout(function() {{ invoke_static_method ('[debugger-test] DebuggerTests.EvaluateLocalsWithIndexingTests:EvaluateLocals'); 1 }})",
+            wait_for_event_fn: async (pause_location) =>
+            {
+                // indexing with expression of a wrong type
+                var id = pause_location["callFrames"][0]["callFrameId"].Value<string>();
+                var (_, res) = await EvaluateOnCallFrame(id, "f.numList[\"a\" + 1]", expect_ok: false );
+                Assert.Equal("Unable to evaluate element access 'f.numList[\"a\" + 1]': Cannot index with an object of type 'string'", res.Error["message"]?.Value<string>());
+            });
+
+        [ConditionalFact(nameof(RunningOnChrome))]
+        public async Task EvaluateIndexingByExpressionContainingUnknownIdentifier() => await CheckInspectLocalsAtBreakpointSite(
+            "DebuggerTests.EvaluateLocalsWithIndexingTests", "EvaluateLocals", 5, "DebuggerTests.EvaluateLocalsWithIndexingTests.EvaluateLocals",
+            $"window.setTimeout(function() {{ invoke_static_method ('[debugger-test] DebuggerTests.EvaluateLocalsWithIndexingTests:EvaluateLocals'); 1 }})",
+            wait_for_event_fn: async (pause_location) =>
+            {
+                // indexing with expression of a wrong type
+                var id = pause_location["callFrames"][0]["callFrameId"].Value<string>();
+                var (_, res) = await EvaluateOnCallFrame(id, "f.numList[\"a\" + x]", expect_ok: false);
+                Assert.Equal("The name x does not exist in the current context", res.Error["result"]?["description"]?.Value<string>());
+            });
+
         [Fact]
         public async Task EvaluateIndexingByMemberVariables() => await CheckInspectLocalsAtBreakpointSite(
             "DebuggerTests.EvaluateLocalsWithIndexingTests", "EvaluateLocals", 5, "DebuggerTests.EvaluateLocalsWithIndexingTests.EvaluateLocals",
@@ -642,7 +697,6 @@ await EvaluateOnCallFrameAndCheck(id,
                    ("f.textList[f.idx1]", TString("2")),
                    ("f.numArray[f.idx1]", TNumber(2)),
                    ("f.textArray[f.idx0]", TString("1")));
-
            });
 
         [Fact]

src/mono/wasm/debugger/tests/debugger-test/debugger-evaluate-test.cs

@@ -519,6 +519,8 @@ public class TestEvaluate
             public int idx0;
             public int idx1;
 
+            public bool this[string key] => key.Length > 3;
+
             public void run()
             {
                 numList = new List<int> { 1, 2 };