Merge pull request #41845 from jnm2/your_other_left

Fixes the bug reported very kindly by @martinstenhoff at #40066 (comment).

Fixes #41826, same bug

src/EditorFeatures/CSharpTest/SimplifyInterpolation/SimplifyInterpolationTests.cs

@@ -198,7 +198,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,-3} suffix"";
+        _ = $""prefix {someValue,3} suffix"";
     }
 }");
         }
@@ -218,13 +218,13 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,3} suffix"";
+        _ = $""prefix {someValue,-3} suffix"";
     }
 }");
         }
 
         [Fact]
-        public async Task PadLeftWithComplexConstantExpressionRequiringParentheses()
+        public async Task PadLeftWithComplexConstantExpression()
         {
             await TestInRegularAndScriptAsync(
 @"class C
@@ -240,7 +240,7 @@ void M(string someValue)
     void M(string someValue)
     {
         const int someConstant = 1;
-        _ = $""prefix {someValue,-((byte)3.3 + someConstant)} suffix"";
+        _ = $""prefix {someValue,(byte)3.3 + someConstant} suffix"";
     }
 }");
         }
@@ -260,7 +260,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,-3} suffix"";
+        _ = $""prefix {someValue,3} suffix"";
     }
 }");
         }
@@ -280,7 +280,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,3} suffix"";
+        _ = $""prefix {someValue,-3} suffix"";
     }
 }");
         }
@@ -312,7 +312,7 @@ void M(string someValue)
         }
 
         [Fact]
-        public async Task PadRightWithComplexConstantExpression()
+        public async Task PadRightWithComplexConstantExpressionRequiringParentheses()
         {
             await TestInRegularAndScriptAsync(
 @"class C
@@ -328,7 +328,7 @@ void M(string someValue)
     void M(string someValue)
     {
         const int someConstant = 1;
-        _ = $""prefix {someValue,(byte)3.3 + someConstant} suffix"";
+        _ = $""prefix {someValue,-((byte)3.3 + someConstant)} suffix"";
     }
 }");
         }
@@ -420,7 +420,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,-3:goo} suffix"";
+        _ = $""prefix {someValue,3:goo} suffix"";
     }
 }");
         }
@@ -440,7 +440,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,3:goo} suffix"";
+        _ = $""prefix {someValue,-3:goo} suffix"";
     }
 }");
         }
@@ -511,7 +511,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue,-3} suffix"";
+        _ = $""prefix {someValue,3} suffix"";
     }
 }");
         }
@@ -568,7 +568,7 @@ void M(string someValue)
 {
     void M(string someValue)
     {
-        _ = $""prefix {someValue.PadLeft(3),3} suffix"";
+        _ = $""prefix {someValue.PadLeft(3),-3} suffix"";
     }
 }");
         }

src/Features/Core/Portable/SimplifyInterpolation/Helpers.cs

@@ -131,7 +131,7 @@ private static TextSpan GetSpanWithinLiteralQuotes(IVirtualCharService virtualCh
 
                             unwrapped = invocation.Instance;
                             alignment = alignmentSyntax as TExpressionSyntax;
-                            negate = targetName == nameof(string.PadLeft);
+                            negate = targetName == nameof(string.PadRight);
 
                             unnecessarySpans.AddRange(invocation.Syntax.Span
                                 .Subtract(invocation.Instance.Syntax.FullSpan)