Add detection of leading-dot when the contextual type is String ` to `optional_data_string_conversion` rule by nadeemnali · Pull Request #6372 · realm/SwiftLint

nadeemnali · 2025-12-09T21:23:57Z

Summary

The optional_data_string_conversion SwiftSyntax rule only detected direct calls like:

String(decoding: data, as: UTF8.self)

but it missed two common variants:

Type-qualified initializer: String.init(decoding: data, as: UTF8.self)
Leading dot initializer used with an explicit type annotation: let text: String = .init(decoding: data, as: UTF8.self)

This change updates the rule to detect both String.init(...) and leading-dot .init(...) when the contextual type is String. It also adds examples to the rule description and a unit test that verifies the rule's description examples.

Changes

Update OptionalDataStringConversionRule visitor to:
- keep existing detection for direct String(...) calls,
- detect String.init(...) (MemberAccessExpr with base String and member init),
- detect leading-dot .init(...) when assigned to a variable with an explicit String type annotation.
Add a test file which runs the rule's description examples.

Why

This fixes the bug reported where
let text: String = .init(decoding: data, as: UTF8.self) did not produce the expected lint violation.

Test plan

Unit test included: Tests/SwiftLintBuiltInRulesTests/OptionalDataStringConversionRuleTests.swift
The test verifies the rule's nonTriggering and triggering examples contained in the RuleDescription.

SwiftLintBot · 2025-12-09T21:31:47Z

	19 Messages
📖	Building this branch resulted in a binary size of 27363.16 KiB vs 27357.74 KiB when built on `main` (0% larger).
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📖	Linting Swift with this PR took 4.6 s vs 4.67 s on `main` (1% faster).
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Generated by 🚫 Danger

SimplyDanny

Thanks for preparing the PR! Please consider my comments.

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

Tests/BuiltInRulesTests/OptionalDataStringConversionRuleTests.swift

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

CHANGELOG.md

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

SimplyDanny · 2026-02-19T19:27:19Z

Hey @nadeemnali, is anything blocking you from moving this forward?

nadeemnali · 2026-02-24T08:13:51Z

Hey @nadeemnali, is anything blocking you from moving this forward?

Hey @SimplyDanny Apologies, I was busy for past weeks, will update the comments ASAP

nadeemnali · 2026-02-25T07:49:34Z

@SimplyDanny Can you please help me with the danger issue in pipeline, can't seem to find any logs for the failure

SimplyDanny · 2026-02-25T08:47:29Z

@SimplyDanny Can you please help me with the danger issue in pipeline, can't seem to find any logs for the failure

Danger doesn't like merge commits. Please rebase your branch onto main instead.

SimplyDanny

Thanks for addressing my remarks! There is one more thing about allowing .init(...) even without an explicit type optionally.

CHANGELOG.md

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

SimplyDanny · 2026-03-05T21:21:59Z

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

        name: "Optional Data -> String Conversion",
-        description: "Prefer failable `String(bytes:encoding:)` initializer when converting `Data` to `String`",
+        description: """
+            Prefer failable `String(bytes:encoding:)` initializer when converting `Data` to `String`. \


I'd rather keep it as is. Mentioning configuration parameters here increases the maintenance effort.

SimplyDanny · 2026-03-05T21:23:19Z

...iftLintBuiltInRules/Rules/RuleConfigurations/OptionalDataStringConversionConfiguration.swift

+    private(set) var severityConfiguration = SeverityConfiguration<Parent>.warning
+
+    // When true, also flag leading-dot `.init(decoding:as:)` without explicit `String` type annotation.
+    // Default is false to preserve conservative behavior.


Skip that last sentence. Should be clear even without it.

SimplyDanny · 2026-03-05T21:25:17Z

Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift

-            Example("String(decoding: data, as: UTF8.self)")
+            Example("String(decoding: data, as: UTF8.self)"),
+            Example("String.init(decoding: data, as: UTF8.self)"),
+            Example("let text: String = .init(decoding: data, as: UTF8.self)"),


Tests (triggering and non-triggering) are missing for the new option. Just add them here with a configuration.

…ting the arbitrary tree walking.

…ersion rule

SimplyDanny linked an issue Dec 9, 2025 that may be closed by this pull request

optional_data_string_conversion does not trigger when .init(decoding:as:) is called instead of String(decoding:as:) #6359

Open

2 tasks

SimplyDanny requested changes Dec 9, 2025

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nadeemnali requested a review from SimplyDanny December 11, 2025 19:05

nadeemnali force-pushed the feature/large-tuple-ignore-regex branch from 804ec4c to 4cfbd90 Compare December 16, 2025 21:19

SimplyDanny requested changes Dec 17, 2025

View reviewed changes

This was referenced Feb 14, 2026

Support String.init and .init syntax in optional_data_string_conversion #6495

Closed

Fix optional_data_string_conversion not triggering for .init(decoding:as:) #6503

Closed

nadeemnali force-pushed the feature/large-tuple-ignore-regex branch from 5de3ae6 to a7dd1f5 Compare February 25, 2026 12:53

SimplyDanny mentioned this pull request Feb 25, 2026

Add optional shorthand .init support to optional_data_string_conversion #6508

Closed

nadeemnali force-pushed the feature/large-tuple-ignore-regex branch 13 times, most recently from bd3286e to 13b6617 Compare February 26, 2026 16:17

SimplyDanny reviewed Feb 28, 2026

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Source/SwiftLintBuiltInRules/Rules/Lint/OptionalDataStringConversionRule.swift Show resolved Hide resolved

nadeemnali force-pushed the feature/large-tuple-ignore-regex branch from 5160e5b to 7b74331 Compare March 1, 2026 11:57

SimplyDanny requested changes Mar 5, 2026

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nadeemnali added 15 commits March 8, 2026 12:53

Updated 'if let' to use guard statement also updated logic to elimina…

fadbe15

…ting the arbitrary tree walking.

Minor fixes

b7130c5

Updated lint issues

78917bd

Update changelog

f4125b6

Moved ChangeLog to main

ba2d1e5

Detect String.init and leading-dot init in optional_data_string_conv…

dfc5776

…ersion rule

Update unit tests

51bc101

Update linting issues

8ca37bb

Update to use visitPost(_ node: FunctionCallExprSyntax)

770b2fe

Updated ChangeLog

fe3cd9a

Changelog lint

3ec27b9

Adds configuration for implicit init

e565c2d

Updated lint issues

b64c80e

Added Default test value

ddbb7bf

Updated Triggering example

6faf8d2

nadeemnali force-pushed the feature/large-tuple-ignore-regex branch from 6098bab to 6faf8d2 Compare March 8, 2026 13:27

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nadeemnali commented Dec 9, 2025

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SwiftLintBot commented Dec 9, 2025 •

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