harden(vtag): exclude backslash from passthrough capture + parity tests (A review)

2026-06-07 15:31:54 -04:00
parent 08d7477860
commit b73ce75402
3 changed files with 62 additions and 1 deletions
@@ -200,6 +200,38 @@ public sealed class RoslynVirtualTagEvaluatorTests
        result.Reason.ShouldBeNull();
    }

+    /// <summary>Direct parity test: the EXACT mirror source <c>return ctx.GetTag("missing").Value;</c>
+    /// evaluated against an empty dependency dictionary takes the fast-path and yields
+    /// <c>Ok(null)</c>; a minimally-altered but semantically-identical non-passthrough variant
+    /// <c>return (object?)ctx.GetTag("missing").Value;</c> compiled by Roslyn against the same
+    /// empty deps yields the identical <c>Ok(null)</c> — proving the fast-path is byte-identical
+    /// to the Roslyn path for the missing-dependency case.</summary>
+    [Fact]
+    public void Passthrough_exact_mirror_missing_dep_matches_Roslyn_baseline()
+    {
+        using var sut = new RoslynVirtualTagEvaluator(NullLogger<RoslynVirtualTagEvaluator>.Instance);
+
+        // Fast-path: exact mirror shape → passthrough returns Ok(null) for missing dep.
+        var fastPath = sut.Evaluate(
+            "vt-parity-fast",
+            "return ctx.GetTag(\"missing\").Value;",
+            new Dictionary<string, object?>());
+
+        fastPath.Success.ShouldBeTrue(fastPath.Reason);
+        fastPath.Value.ShouldBeNull();
+        fastPath.Reason.ShouldBeNull();
+
+        // Roslyn path: `(object?)` cast forces compilation but reads the same missing tag.
+        var roslynPath = sut.Evaluate(
+            "vt-parity-roslyn",
+            "return (object?)ctx.GetTag(\"missing\").Value;",
+            new Dictionary<string, object?>());
+
+        roslynPath.Success.ShouldBeTrue(roslynPath.Reason);
+        roslynPath.Value.ShouldBeNull();
+        roslynPath.Reason.ShouldBeNull();
+    }
+
    /// <summary>Decisive proof the fast-path skips Roslyn: the compiled-script cache (which every
    /// Roslyn evaluation populates via <c>GetOrAdd</c>) stays EMPTY after a mirror evaluation, then
    /// grows to one entry once a genuine (non-mirror) expression forces compilation.</summary>