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Merge pull request #21726 from hvitved/csharp/useless-to-string-fps

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C#: Fix FPs in `RedundantToStringCall.ql`
This commit is contained in:
Tom Hvitved
2026-04-17 14:59:22 +02:00
committed by GitHub
parent 3073c1c94c 7bfdfbefa9
commit 14bdb62cf8
7 changed files with 31 additions and 12 deletions
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2
csharp/ql/lib/semmle/code/csharp/commons/Strings.qll
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@@ -29,7 +29,7 @@ class ImplicitToStringExpr extends Expr {
m = p.getCallable()
|
m = any(SystemTextStringBuilderClass c).getAMethod() and
m.getName().regexpMatch("Append(Line)?") and
m.getName() = "Append" and
not p.getType() instanceof ArrayType
or
p instanceof StringFormatItemParameter and

5
csharp/ql/src/Useless code/RedundantToStringCall.ql
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@@ -18,5 +18,6 @@ import semmle.code.csharp.frameworks.System
from MethodCall mc
where
mc instanceof ImplicitToStringExpr and
mc.getTarget() instanceof ToStringMethod
select mc, "Redundant call to 'ToString' on a String object."
mc.getTarget() instanceof ToStringMethod and
not mc.getQualifier() instanceof BaseAccess
select mc, "Redundant call to 'ToString'."

7
csharp/ql/src/change-notes/2026-04-17-useless-to-string.md Normal file
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@@ -0,0 +1,7 @@
---
category: minorAnalysis
---
* The query `cs/useless-tostring-call` has been updated to avoid false
positive results in calls to `StringBuilder.AppendLine` and calls of
the form `base.ToString()`. Moreover, the alert message has been
made more precise.

14
csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.cs
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@@ -1,16 +1,24 @@
using System;
using System.Text;
class RedundantToString
{
public void M(object o)
{
Console.WriteLine(o.ToString()); // BAD
Console.WriteLine(o.ToString()); // $ Alert
Console.WriteLine(o); // GOOD
Console.WriteLine($"Hello: {o.ToString()}"); // BAD
Console.WriteLine($"Hello: {o.ToString()}"); // $ Alert
Console.WriteLine($"Hello: {o}"); // GOOD
Console.WriteLine("Hello: " + o.ToString()); // BAD
Console.WriteLine("Hello: " + o.ToString()); // $ Alert
Console.WriteLine("Hello: " + o); // GOOD
var sb = new StringBuilder();
sb.Append(o.ToString()); // $ Alert
sb.Append(o); // GOOD
sb.AppendLine(o.ToString()); // GOOD
Console.WriteLine($"Hello: {base.ToString()}"); // GOOD
}
}

9
csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.expected
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@@ -1,4 +1,5 @@
| RedundantToStringCall.cs:7:27:7:38 | call to method ToString | Redundant call to 'ToString' on a String object. |
| RedundantToStringCall.cs:10:37:10:48 | call to method ToString | Redundant call to 'ToString' on a String object. |
| RedundantToStringCall.cs:13:39:13:50 | call to method ToString | Redundant call to 'ToString' on a String object. |
| RedundantToStringCallBad.cs:7:45:7:56 | call to method ToString | Redundant call to 'ToString' on a String object. |
| RedundantToStringCall.cs:8:27:8:38 | call to method ToString | Redundant call to 'ToString'. |
| RedundantToStringCall.cs:11:37:11:48 | call to method ToString | Redundant call to 'ToString'. |
| RedundantToStringCall.cs:14:39:14:50 | call to method ToString | Redundant call to 'ToString'. |
| RedundantToStringCall.cs:18:19:18:30 | call to method ToString | Redundant call to 'ToString'. |
| RedundantToStringCallBad.cs:7:45:7:56 | call to method ToString | Redundant call to 'ToString'. |

4
csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCall.qlref
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@@ -1 +1,3 @@
Useless code/RedundantToStringCall.ql
query: Useless code/RedundantToStringCall.ql
postprocess:
- utils/test/InlineExpectationsTestQuery.ql

2
csharp/ql/test/query-tests/Useless Code/RedundantToStringCall/RedundantToStringCallBad.cs
View File

@@ -4,6 +4,6 @@ class Bad
{
static string Hello(object o)
{
return string.Format("Hello, {0}!", o.ToString());
return string.Format("Hello, {0}!", o.ToString()); // $ Alert
}
}