Fix Timeout's TimeoutGenerator documentation

docs/strategies/timeout.md

@@ -117,8 +117,11 @@ catch (TimeoutRejectedException)
 | `TimeoutGenerator` | `null`        | This delegate allows you to **dynamically** calculate the timeout period by utilizing information that is only available at runtime. |
 | `OnTimeout`        | `null`        | If provided then it will be invoked after the timeout occurred.                                                                      |
 
-> [!NOTE]
-> If both `Timeout` and `TimeoutGenerator` are specified then `Timeout` will be ignored.
+### Timeout duration calculation
+
+- If `TimeoutGenerator` is not specified then `Timeout` will be used.
+- If both `Timeout` and `TimeoutGenerator` are specified then `Timeout` will be ignored.
+- If `TimeoutGenerator` returns a `TimeSpan` that is less than or equal to `TimeSpan.Zero` then the strategy will have no effect.
 
 ### `OnTimeout` versus catching `TimeoutRejectedException`
 

src/Polly.Core/Timeout/TimeoutStrategyOptions.cs

@@ -27,8 +27,9 @@ public class TimeoutStrategyOptions : ResilienceStrategyOptions
     /// Gets or sets a timeout generator that generates the timeout for a given execution.
     /// </summary>
     /// <remarks>
-    /// If generator returns a <see cref="TimeSpan"/> value that is less or equal to <see cref="TimeSpan.Zero"/>
-    /// its value is ignored and <see cref="Timeout"/> is used instead. When generator is <see langword="null"/> the <see cref="Timeout"/> is used.
+    /// When generator is <see langword="null"/> then the <see cref="Timeout"/> property's value is used instead.
+    /// When generator returns a <see cref="TimeSpan"/> value that is less than or equal to <see cref="TimeSpan.Zero"/>
+    /// then the strategy will do nothing.
     /// <para>
     /// Return <see cref="System.Threading.Timeout.InfiniteTimeSpan"/> to disable the timeout for the given execution.
     /// </para>

test/Polly.Core.Tests/Timeout/TimeoutResilienceStrategyTests.cs

@@ -117,6 +117,36 @@ await sut
             .WithMessage("The operation didn't complete within the allowed timeout of '00:00:02'.");
     }
 
+    [Fact]
+    public async Task Execute_TimeoutGeneratorIsNull_FallsBackToTimeout()
+    {
+        var called = false;
+        var timeout = TimeSpan.FromMilliseconds(10);
+        _options.TimeoutGenerator = null;
+        _options.Timeout = timeout;
+
+        _options.OnTimeout = args =>
+        {
+            called = true;
+            args.Timeout.Should().Be(timeout);
+            return default;
+        };
+
+        var sut = CreateSut();
+        await sut
+        .Invoking(s => s.ExecuteAsync(async token =>
+        {
+            var delay = _timeProvider.Delay(TimeSpan.FromMilliseconds(50), token);
+            _timeProvider.Advance(timeout);
+            await delay;
+        },
+        CancellationToken.None)
+        .AsTask())
+        .Should().ThrowAsync<TimeoutRejectedException>();
+
+        called.Should().BeTrue();
+    }
+
     [Fact]
     public async Task Execute_Timeout_EnsureStackTrace()
     {