Add configurable VariableNameTransformation to EnvironmentVariables config#127503
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…onfig (dotnet#125137) Adds: - AddEnvironmentVariables(prefix, variableNameTransformation) overload on IConfigurationBuilder. - EnvironmentVariablesConfigurationSource.VariableNameTransformation: a settable property that, when non-null, replaces the default transformation behavior. - EnvironmentVariablesConfigurationSource.DefaultTransformation: the existing default that replaces __ with the configuration key delimiter (:). - EnvironmentVariablesConfigurationSource.ColonAndDotTransformation: replaces ___ with . and __ with :, allowing dots in configuration keys without the override-by-environment ergonomics being limited to colons. ColonAndDotTransformation is implemented with ValueStringBuilder on .NET and StringBuilder on .NET Framework. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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svick
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Apr 28, 2026
tarekgh
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tarekgh
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tarekgh
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rosebyte
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LGTM, I left couple suggestions, none of them blocking.
mrek-msft
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May 18, 2026
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Implements #125137.
API additions
IConfigurationBuilder.AddEnvironmentVariables(string? prefix, Func<string, string>? variableNameTransformation)overload.EnvironmentVariablesConfigurationSource.VariableNameTransformation-- a settableFunc<string, string>?that, when non-null, completely replaces the default transformation.EnvironmentVariablesConfigurationSource.DefaultTransformation-- the existing default that replaces__with the configuration key delimiter (:).EnvironmentVariablesConfigurationSource.ColonAndDotTransformation-- replaces___with.and__with:, so configuration keys containing dots can be set from environment variables.API shape matches @bartonjs's approval comment on the issue.
Implementation notes
ColonAndDotTransformationusesValueStringBuilder+stackalloc char[256]on .NET,StringBuilderon .NET Framework, kept under a single small#if NETregion. No new package references.Prefixis itself passed through the active transformation before comparison, so it should be specified in pre-transformation form (e.g."Logging__"rather than"Logging:"). Documented in<remarks>on thePrefixproperty and the matching overloads.Tests
13 new tests in
EnvironmentVariablesTestcover:[Theory]tables for double/triple/4/5/6 underscores, single-underscore preservation, no-underscore early return).VariableNameTransformationreplacing the default, identity transformation disabling replacement, transformation applied to prefix, source/builder wiring, and a behavioral check thatColonAndDotTransformationis not the default.Note
This PR description and the implementation were drafted with assistance from GitHub Copilot.