Align API surface of immutable collections and their corresponding builder types

src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs

@@ -267,7 +267,7 @@ public void Insert(int index, T item) { }
             public int LastIndexOf(T item, int startIndex, int count, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
             public System.Collections.Immutable.ImmutableArray<T> MoveToImmutable() { throw null; }
             public bool Remove(T element) { throw null; }
-            public void Remove(T element, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
+            public bool Remove(T element, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
             public void RemoveAll(Predicate<T> match) { throw null; }
             public void RemoveAt(int index) { }
             public void RemoveRange(int index, int length) { throw null; }
@@ -718,7 +718,7 @@ public void InsertRange(int index, System.Collections.Generic.IEnumerable<T> ite
             public int LastIndexOf(T item, int startIndex, int count) { throw null; }
             public int LastIndexOf(T item, int startIndex, int count, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
             public bool Remove(T item) { throw null; }
-            public void Remove(T item, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
+            public bool Remove(T item, System.Collections.Generic.IEqualityComparer<T>? equalityComparer) { throw null; }
             public int RemoveAll(System.Predicate<T> match) { throw null; }
             public void RemoveAt(int index) { }
             public void RemoveRange(int index, int count) { throw null; }

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Builder.cs

@@ -463,6 +463,7 @@ public void AddRange<TDerived>(ImmutableArray<TDerived>.Builder items) where TDe
 
             /// <summary>
             /// Removes the first occurrence of the specified element from the builder.
+            /// If no match is found, the builder remains unchanged.
             /// </summary>
             /// <param name="element">The element.</param>
             /// <returns>A value indicating whether the specified element was found and removed from the collection.</returns>
@@ -486,14 +487,17 @@ public bool Remove(T element)
             /// The equality comparer to use in the search.
             /// If <c>null</c>, <see cref="EqualityComparer{T}.Default"/> is used.
             /// </param>
-            public void Remove(T element, IEqualityComparer<T>? equalityComparer)
+            public bool Remove(T element, IEqualityComparer<T>? equalityComparer)
             {
                 int index = this.IndexOf(element, 0, _count, equalityComparer);
 
                 if (index >= 0)
                 {
                     this.RemoveAt(index);
+                    return true;
                 }
+
+                return false;
             }
 
             /// <summary>

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList_1.Builder.cs

@@ -758,13 +758,16 @@ public int RemoveAll(Predicate<T> match)
             /// The equality comparer to use in the search.
             /// If <c>null</c>, <see cref="EqualityComparer{T}.Default"/> is used.
             /// </param>
-            public void Remove(T item, IEqualityComparer<T>? equalityComparer)
+            public bool Remove(T item, IEqualityComparer<T>? equalityComparer)
             {
                 int index = this.IndexOf(item, 0, this.Count, equalityComparer);
                 if (index >= 0)
                 {
                     this.RemoveAt(index);
+                    return true;
                 }
+
+                return false;
             }
 
             /// <summary>

src/libraries/System.Collections.Immutable/tests/ImmutableArrayBuilderTest.cs

@@ -336,7 +336,7 @@ public void Remove_EqualityComparer()
             var builder = ImmutableArray.Create(1.5, 2.5, 3.5).ToBuilder();
             var absComparer = new DelegateEqualityComparer<double>(equals: (x, y) => Math.Abs(x) == Math.Abs(y));
 
-            builder.Remove(-1.5, absComparer);
+            Assert.True(builder.Remove(-1.5, absComparer));
             Assert.Equal(new[] { 2.5, 3.5 }, builder);
         }
 

src/libraries/System.Collections.Immutable/tests/ImmutableListBuilderTest.cs

@@ -201,11 +201,11 @@ public void Remove_EqualityComparer()
             mutable.Add(2.4);
             mutable.Add(3.6);
 
-            mutable.Remove(2.4, null);
+            Assert.True(mutable.Remove(2.4, null));
             Assert.Equal(new[] { 1.5, 3.6 }, mutable);
 
             var absComparer = new DelegateEqualityComparer<double>(equals: (x, y) => Math.Abs(x) == Math.Abs(y));
-            mutable.Remove(-1.5, absComparer);
+            Assert.True(mutable.Remove(-1.5, absComparer));
             Assert.Equal(new[] { 3.6 }, mutable);
         }