internal imports by default, only enable warnings as errors in CI

.github/workflows/Documentation.yml

@@ -15,20 +15,20 @@ jobs:
         name: Ubuntu 24.04
 
         steps:
-            -   name: Install Swift
+            -   name: 🤍 Install Swift 🤍
                 uses: tayloraswift/swift-install-action@master
                 with:
                     swift-prefix: "swift-6.2.4-release/ubuntu2404/swift-6.2.4-RELEASE"
                     swift-id: "swift-6.2.4-RELEASE-ubuntu24.04"
 
-            -   name: Install Unidoc
+            -   name: 🤍 Install Unidoc 🤍
                 uses: tayloraswift/swift-unidoc-action@master
 
             #   This clobbers everything in the current directory!
-            -   name: Checkout repository
-                uses: actions/checkout@v3
+            -   name: 🤍 Checkout repository 🤍
+                uses: actions/checkout@v6
 
-            -   name: Validate documentation
+            -   name: 🤍 Validate documentation 🤍
                 run: |
                     unidoc compile \
                     --swift-toolchain $SWIFT_INSTALLATION \
@@ -39,16 +39,16 @@ jobs:
         runs-on: macos-26
         name: macOS
         steps:
-            -   name: Install Unidoc
+            -   name: 🤍 Install Unidoc 🤍
                 uses: tayloraswift/swift-unidoc-action@master
 
-            -   name: Checkout repository
-                uses: actions/checkout@v3
+            -   name: 🤍 Checkout repository 🤍
+                uses: actions/checkout@v6
 
-            -   name: Select Xcode 26.3
+            -   name: 🤍 Select Xcode 26.3 🤍
                 run: sudo xcode-select -s /Applications/Xcode_26.3.app/Contents/Developer
 
-            -   name: Validate documentation
+            -   name: 🤍 Validate documentation 🤍
                 run: |
                     unidoc build \
                     --ci fail-on-errors \

.github/workflows/Tests.yml

@@ -7,31 +7,56 @@ on:
         branches: [ master ]
 
 jobs:
+    changes:
+        runs-on: ubuntu-latest
+        name: Assess changes
+        steps:
+            -   name: 💖 Checkout repository 💖
+                uses: actions/checkout@v6
+
+            -   name: 💖 Decide checks 💖
+                uses: tj-actions/changed-files@v47
+                id: changes
+                with:
+                    files_ignore: |
+                        README.md
+                        LICENSE
+                        NOTICE
+                        .mailmap
+                        .gitignore
+                        .github/FUNDING.yml
+        outputs:
+            code_changed: ${{ steps.changes.outputs.any_changed }}
+
     linux:
         runs-on: ubuntu-24.04
         name: Ubuntu 24.04
+        needs: changes
+        if: ${{ needs.changes.outputs.code_changed == 'true' }}
         steps:
-            -   name: Install Swift
+            -   name: 💖 Install Swift 💖
                 uses: tayloraswift/swift-install-action@master
                 with:
                     swift-prefix: "swift-6.2.4-release/ubuntu2404/swift-6.2.4-RELEASE"
                     swift-id: "swift-6.2.4-RELEASE-ubuntu24.04"
 
-            -   name: Checkout repository
-                uses: actions/checkout@v3
+            -   name: 💖 Checkout repository 💖
+                uses: actions/checkout@v6
 
-            -   name: Run tests
+            -   name: 💖 Run tests 💖
                 run: Scripts/TestAll
 
     macos:
         runs-on: macos-26
         name: macOS
+        needs: changes
+        if: ${{ needs.changes.outputs.code_changed == 'true' }}
         steps:
-            -   name: Checkout repository
-                uses: actions/checkout@v3
+            -   name: 💖 Checkout repository 💖
+                uses: actions/checkout@v6
 
-            -   name: Select Xcode 26.3
+            -   name: 💖 Select Xcode 26.3 💖
                 run: sudo xcode-select -s /Applications/Xcode_26.3.app/Contents/Developer
 
-            -   name: Run tests
+            -   name: 💖 Run tests 💖
                 run: Scripts/TestAll

Package.swift

@@ -1,4 +1,5 @@
 // swift-tools-version:6.2
+import class Foundation.ProcessInfo
 import PackageDescription
 
 let package: Package = .init(
@@ -85,6 +86,14 @@ let package: Package = .init(
         ),
     ]
 )
+
+var WarningsAsErrors: Bool {
+    switch ProcessInfo.processInfo.environment["WARNINGS_AS_ERRORS"] {
+    case "true"?: true
+    case "1"?: true
+    default: false
+    }
+}
 package.targets = package.targets.map {
     switch $0.type {
     case .plugin: return $0
@@ -95,8 +104,12 @@ package.targets = package.targets.map {
         var settings: [SwiftSetting] = $0 ?? []
 
         settings.append(.enableUpcomingFeature("ExistentialAny"))
-        settings.append(.treatWarning("ExistentialAny", as: .error))
-        settings.append(.treatWarning("MutableGlobalVariable", as: .error))
+        settings.append(.enableUpcomingFeature("InternalImportsByDefault"))
+
+        if  WarningsAsErrors {
+            settings.append(.treatWarning("ExistentialAny", as: .error))
+            settings.append(.treatWarning("MutableGlobalVariable", as: .error))
+        }
 
         $0 = settings
     } (&$0.swiftSettings)

Scripts/TestAll

@@ -1,5 +1,9 @@
 #!/bin/bash
-set -e
+set -euo pipefail
+
+export WARNINGS_AS_ERRORS=1
+
 swift --version
 swift test
-swift build -c release
+swift build -c release \
+    --explicit-target-dependency-import-check=error

Sources/JSONDecoding/Decoding/JSON.DecodingError.swift

@@ -1,4 +1,4 @@
-import TraceableErrors
+public import TraceableErrors
 
 extension JSON {
     /// An error occurred while decoding a document field.

Sources/JSONParsing/JSON.Array (ext).swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 import JSONAST
 
 extension JSON.Array {

Sources/JSONParsing/JSON.Node (ext).swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 import JSONAST
 
 extension JSON.Node {

Sources/JSONParsing/JSON.Object (ext).swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 import JSONAST
 
 extension JSON.Object {

Sources/JSONParsing/Rules/JSON (ext).swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     typealias CommaRule<Location> =

Sources/JSONParsing/Rules/JSON.NodeRule.Array.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// Matches an array literal.

Sources/JSONParsing/Rules/JSON.NodeRule.False.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// A literal `false` expression.

Sources/JSONParsing/Rules/JSON.NodeRule.Inf.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     enum Inf: LiteralRule {

Sources/JSONParsing/Rules/JSON.NodeRule.NaN.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// A literal `nan` expression, all lowercase.

Sources/JSONParsing/Rules/JSON.NodeRule.Nonfinite.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     enum Nonfinite: ParsingRule {

Sources/JSONParsing/Rules/JSON.NodeRule.Null.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// A literal `null` expression.

Sources/JSONParsing/Rules/JSON.NodeRule.Object.Item.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule.Object {
     /// Matches an key-value expression.

Sources/JSONParsing/Rules/JSON.NodeRule.Object.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// Matches an object literal.

Sources/JSONParsing/Rules/JSON.NodeRule.True.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NodeRule {
     /// A literal `true` expression.

Sources/JSONParsing/Rules/JSON.NodeRule.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     /// Matches any value, including fragment values.

Sources/JSONParsing/Rules/JSON.NumberRule.PlusOrMinus.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.NumberRule {
     /// Matches an ASCII `+` or `-` sign.

Sources/JSONParsing/Rules/JSON.NumberRule.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     /// Matches a numeric literal.

Sources/JSONParsing/Rules/JSON.RootRule.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     /// All of the parsing rules in this library are defined at the UTF-8 level.

Sources/JSONParsing/Rules/JSON.StringRule.CodeUnit.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.StringRule {
     /// Matches a UTF-8 code unit that is allowed to appear inline in a string literal.

Sources/JSONParsing/Rules/JSON.StringRule.EscapeSequence.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.StringRule {
     /// Matches a sequence of escaped UTF-16 code units.

Sources/JSONParsing/Rules/JSON.StringRule.EscapedCodeUnit.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON.StringRule {
     /// Matches an ASCII character (besides `u`) that is allowed to

Sources/JSONParsing/Rules/JSON.StringRule.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     /// Matches a string literal.

Sources/JSONParsing/Rules/JSON.WhitespaceRule.swift

@@ -1,4 +1,4 @@
-import Grammar
+internal import Grammar
 
 extension JSON {
     /// Matches the whitespace characters U+0020, `\t`, `\n`, and `\r`.

Sources/JavaScriptPersistence/JSObject.swift

@@ -1,4 +1,4 @@
-import JSON
+public import JSON
 
 public final class JSObject {
     @usableFromInline var object: [String: JSValue]

Sources/JavaScriptPersistence/JSValue.swift

@@ -1,4 +1,4 @@
-import JSON
+public import JSON
 
 @frozen public struct JSValue {
     @usableFromInline let storage: Storage