Fix type mismatch error in `reflowMultilineStringLiterals` #979

dongdong867 · 2025-04-05T21:39:18Z

Problem description

Environment: swift-format with v601.0.0 or build-in support with Xcode 16.3
Issue:
When running swift-format <path> command with a custom configuration that contains reflowMultilineStringLiterals will receive the below error
```
<unknown>: error: Unable to read configuration for <path-to-file>: The data couldn’t be read because it isn’t in the correct format.
```
How to reproduce:
1. Create a .swift-format config file in any project with swift-format setup
2. Make sure the config file contains the setting of reflowMultilineStringLiterals based on the document.
3. Run the swift-format <path> command and the error should show in the console

Root cause

The MultilineStringReflowBehavior enum in /Sources/SwiftFormat/API/Configuration.swift is used to parse the value of reflowMultilineStringLiterals from the config file, however, the origin enum raw type is missing which causes the decodeIfPresent(_:forKey:) function throws an DecodingError.typeMismatch error when decoding.

The root cause can be verified by running the swift-format dump-configuration command. The console shows that the default value of key reflowMultilineStringLiterals is structured as:

"reflowMultilineStringLiterals" : {
  "never" : {

  }
},

but according to the documentation, the value of ⁠reflowMultilineStringLiterals should be a string like:

"reflowMultilineStringLiterals": "never",

Solution

By adding a raw type String to the enum MultilineStringReflowBehavior:

// Before
enum MultilineStringReflowBehavior: Codable { ... }

// After
enum MultilineStringReflowBehavior: String, Codable { ... }

This solves the current issue and makes the config file align with what is defined in the documentation.

{
  "fileScopedDeclarationPrivacy" : {
    "accessLevel" : "private"
  },
  "indentConditionalCompilationBlocks" : true,
  "indentSwitchCaseLabels" : false,
  "indentation" : {
    "spaces" : 2
  },
  "lineBreakAroundMultilineExpressionChainComponents" : false,
  "lineBreakBeforeControlFlowKeywords" : false,
  "lineBreakBeforeEachArgument" : false,
  "lineBreakBeforeEachGenericRequirement" : false,
  "lineBreakBetweenDeclarationAttributes" : false,
  "lineLength" : 100,
  "maximumBlankLines" : 1,
  "multiElementCollectionTrailingCommas" : true,
  "noAssignmentInExpressions" : {
    "allowedFunctions" : [
      "XCTAssertNoThrow"
    ]
  },
  "prioritizeKeepingFunctionOutputTogether" : false,

  "reflowMultilineStringLiterals" : "never",

  "respectsExistingLineBreaks" : true,
  "rules" : { "...ignored with unchanged" }
  "spacesAroundRangeFormationOperators" : false,
  "spacesBeforeEndOfLineComments" : 2,
  "tabWidth" : 8,
  "version" : 1
}

allevato · 2025-04-07T12:29:57Z

Unfortunately, the current behavior is part of the swift-format release in the 6.1 toolchain (Xcode 16.3), so we can't just add a raw value to this enum without breaking how configurations created for that version of the tool would decode.

What I think we can do is:

Add the String raw value as you've done here, so that future versions use the preferred format
Add a custom implementation of init(from: Decoder) that detects either format: a simple string or an object with a single key.

I think the easiest way to implement (2) would be create a second private copy of the enum without the String raw value, called something like LegacyMultilineStringReflowBehavior. Then, you try to decode it as a String first, and if that fails, try to decode it as the legacy enum. If the first succeeds, convert it with init(rawValue:). If the second succeeds, map it from the legacy enum to the proper enum. If both fail, throw the error.

That would avoid us having to bump the configuration version just for this oversight.

…ngLiterals`

dongdong867 · 2025-04-07T15:54:54Z

@allevato Thanks for your soundness consideration on this issue.

I've implement the legacy private enum based on your comment, and I've also added some document to the reflowMultilineStringLiterals section. Please felt free to leave some comment if there's any thing I need to change.

allevato

Can you please add a couple small tests to Tests/SwiftFormatTests/API/ConfigurationTests.swift that verify that both formats decode correctly, just to make sure we don't accidentally regress this in the future?

allevato · 2025-04-07T16:09:31Z

Sources/SwiftFormat/API/Configuration.swift

+    var isNever: Bool {
+      self == .never
    }

    var isAlways: Bool {
+      self == .always
+    }


I don't think we need these since nothing else in the formatter will access them.

allevato · 2025-04-07T16:12:02Z

Documentation/Configuration.md

+
+> [!NOTE]
+> This setting should be specified as a string value (e.g. "never")
+> For backward compatibility with swift-format version 601.0.0, the configuration also accepts the legacy object format where the setting is specified as an object with a single key (e.g., ⁠{ "never": {} }).


Suggested change

> For backward compatibility with swift-format version 601.0.0, the configuration also accepts the legacy object format where the setting is specified as an object with a single key (e.g., ⁠{ "never": {} }).

> For backward compatibility with swift-format version 601.0.0, the configuration also accepts the legacy object format where the setting is specified as an object with a single key (e.g., `⁠{ "never": {} }`).

dongdong867 · 2025-04-07T16:29:21Z

@allevato comments addressed, please check it again, thx!

allevato · 2025-04-07T16:34:59Z

Can you please add a couple small tests to Tests/SwiftFormatTests/API/ConfigurationTests.swift that verify that both formats decode correctly, just to make sure we don't accidentally regress this in the future?

I think you missed this one 🙂

dongdong867 · 2025-04-07T17:26:55Z

@allevato Sorry for missing the comment, tests are added, please check.

allevato

Thanks! If you accept the suggestions here, I can kick off the tests.

allevato · 2025-04-07T18:02:46Z

Tests/SwiftFormatTests/API/ConfigurationTests.swift

+    typealias MultilineStringReflowBehavior = Configuration.MultilineStringReflowBehavior
+
+    let testCases = [
+      "never": MultilineStringReflowBehavior.never,
+      "always": MultilineStringReflowBehavior.always,
+      "onlyLinesOverLength": MultilineStringReflowBehavior.onlyLinesOverLength,
+    ]


Suggested change

typealias MultilineStringReflowBehavior = Configuration.MultilineStringReflowBehavior

let testCases = [

"never": MultilineStringReflowBehavior.never,

"always": MultilineStringReflowBehavior.always,

"onlyLinesOverLength": MultilineStringReflowBehavior.onlyLinesOverLength,

]

let testCases: [String: Configuration.MultilineStringReflowBehavior] = [

"never": .never,

"always": .always,

"onlyLinesOverLength": .onlyLinesOverLength,

]

allevato · 2025-04-07T18:03:26Z

Tests/SwiftFormatTests/API/ConfigurationTests.swift

+    typealias MultilineStringReflowBehavior = Configuration.MultilineStringReflowBehavior
+
+    let testCases = [
+      "{ \"never\": {} }": MultilineStringReflowBehavior.never,
+      "{ \"always\": {} }": MultilineStringReflowBehavior.always,
+      "{ \"onlyLinesOverLength\": {} }": MultilineStringReflowBehavior.onlyLinesOverLength,
+    ]


Suggested change

typealias MultilineStringReflowBehavior = Configuration.MultilineStringReflowBehavior

let testCases = [

"{ \"never\": {} }": MultilineStringReflowBehavior.never,

"{ \"always\": {} }": MultilineStringReflowBehavior.always,

"{ \"onlyLinesOverLength\": {} }": MultilineStringReflowBehavior.onlyLinesOverLength,

]

let testCases: [String: Configuration.MultilineStringReflowBehavior] = [

"{ \"never\": {} }": .never,

"{ \"always\": {} }": .always,

"{ \"onlyLinesOverLength\": {} }": .onlyLinesOverLength,

]

dongdong867 · 2025-04-07T18:55:21Z

@allevato Addressed, thanks for your review!

allevato · 2025-04-07T19:11:23Z

This looks like a bug in API digester:

4 breaking changes detected in SwiftFormat:
  💔 API breakage: func Configuration.MultilineStringReflowBehavior.hash(into:) has been removed
  💔 API breakage: func Configuration.MultilineStringReflowBehavior.encode(to:) has been removed
  💔 API breakage: var Configuration.MultilineStringReflowBehavior.hashValue has been removed
  💔 API breakage: constructor Configuration.MultilineStringReflowBehavior.init(from:) has been removed

Adding a raw value to the enum certainly shouldn't have removed any of those declarations; the type is still Hashable and Codable.

@ahoppen What do you think? I'm inclined to say that @dongdong867 should just copy these into api-breakages.txt but I wanted to call this out first in case I'm missing something.

ahoppen · 2025-04-08T00:10:02Z

Let’s add them to api-breakages.txt and reconsider the value of the API breakage check separately.

dongdong867 · 2025-04-08T00:30:29Z

@allevato @ahoppen Value added to api-breakages.txt, please review, thanks.

allevato

Thank you for fixing this!

…#979)

Add String raw type to MultilineStringReflowBehavior

c13cd26

dongdong867 requested review from ahoppen, allevato, bnbarham and shawnhyam as code owners April 5, 2025 21:39

dongdong867 mentioned this pull request Apr 6, 2025

Errors using reflowMultilineStringLiterals #980

Closed

dongdong867 added 3 commits April 7, 2025 23:14

Create a LegacyMultilineStringReflowBehavior to avoid version bump

fbac9f5

Add document and notes for legacy object type in `reflowMultilineStri…

52ca716

…ngLiterals`

refactor: make code in MultilineStringReflowBehavior concise

7de00b4

allevato reviewed Apr 7, 2025

View reviewed changes

dongdong867 added 2 commits April 8, 2025 00:25

Remove unused var getter from LegacyMultilineStringReflowBehavior

1a1f336

Add backquote to value in documentation

adbbbe2

Add test for decoding reflowMultilineStringLiterals

28a70a2

allevato approved these changes Apr 7, 2025

View reviewed changes

Replace dict value with enum shorthand in tests

0927ba6

Add detected breaking changes to api-breakages.txt

547dcfe

allevato approved these changes Apr 8, 2025

View reviewed changes

allevato merged commit 661aa9e into swiftlang:main Apr 8, 2025
20 checks passed

dongdong867 deleted the fix_enum_raw_type_mismatch_in_configuration branch April 8, 2025 15:34

ahoppen pushed a commit to ahoppen/swift-format that referenced this pull request Apr 10, 2025

Fix type mismatch error in reflowMultilineStringLiterals (swiftlang…

2da2fa9

…#979)

	> For backward compatibility with swift-format version 601.0.0, the configuration also accepts the legacy object format where the setting is specified as an object with a single key (e.g., ⁠{ "never": {} }).
	> For backward compatibility with swift-format version 601.0.0, the configuration also accepts the legacy object format where the setting is specified as an object with a single key (e.g., `⁠{ "never": {} }`).

Fix type mismatch error in reflowMultilineStringLiterals #979

Fix type mismatch error in reflowMultilineStringLiterals #979

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dongdong867 commented Apr 5, 2025

Problem description

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Solution

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allevato commented Apr 7, 2025

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Fix type mismatch error in `reflowMultilineStringLiterals` #979

Fix type mismatch error in `reflowMultilineStringLiterals` #979