[Analyzer] Usage of ToString in logging source generator method call sites

[stephentoub]

We should consider an analyzer that flags use of ToString() in call sites to logging methods and suggests reconsidering the shape of the logging method such that it takes a strongly-typed value. In many situations, logging is disabled or set at a log level that will result in a particular event being disabled, and doing the ToString() at the call site is then often unnecessary allocation / expense. For example, given:

[LoggerMessage(EventId = 0, Level = LogLevel.Information, Message = "Excessively large timeout `{timeout}`")]
public static partial void ExcessivelyLargeTimeout(this ILogger logger, string timeout);
...
TimeSpan timeout = ...;
logger.ExcessivelyLargeTimeout(timeout.ToString());

the analyzer would flag the .ToString() and suggest the ExcessivelyLargeTimeout method should be changed to take a TimeSpan instead of a string, with the .ToString() removed from the call site.

Performance rules Category
Severity = suggestion

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Issue Details

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We should consider an analyzer that flags use of ToString() in call sites to logging methods and suggests reconsidering the shape of the logging method such that it takes a strongly-typed value. In many situations, logging is disabled or set at a log level that will result in a particular event being disabled, and doing the ToString() at the call site is then often unnecessary allocation / expense. For example, given:

[LoggerMessage(EventId = 0, Level = LogLevel.Information, Message = "Excessively large timeout `{timeout}`")]
public static partial void ExcessivelyLargeTimeout(this ILogger logger, string timeout);
...
TimeSpan timeout = ...;
logger.ExcessivelyLargeTimeout(timeout.ToString());

the analyzer would flag the .ToString() and suggest the ExcessivelyLargeTimeout method should be changed to take a TimeSpan instead of a string, with the .ToString() removed from the call site.

Author:	stephentoub
Assignees:	-
Labels:	code-analyzer, area-Extensions-Logging
Milestone:	-

[tarekgh]

CC @Youssef1313

[Youssef1313]

Happy to implement once the analyzer is approved.