Trim snippet slice indentation (#348)

When trimming a slice out of a snippet, the slice may span some
deeply nested scope that has indentation, so we don't want to take
those lines as is, because they may be unnecessarily indented when
presented as a slice.

rdar://97696391

Author: bitjammer

Sources/SwiftDocC/Model/Rendering/RenderContentCompiler.swift

@@ -224,7 +224,9 @@ struct RenderContentCompiler: MarkupVisitor {
                 // Render only the slice.
                 let lineRange = requestedLineRange.lowerBound..<min(requestedLineRange.upperBound, snippetMixin.lines.count)
                 let lines = snippetMixin.lines[lineRange]
-                return [RenderBlockContent.codeListing(syntax: snippetMixin.language, code: Array(lines), metadata: nil)]
+                let minimumIndentation = lines.map { $0.prefix { $0.isWhitespace }.count }.min() ?? 0
+                let trimmedLines = lines.map { String($0.dropFirst(minimumIndentation)) }
+                return [RenderBlockContent.codeListing(syntax: snippetMixin.language, code: trimmedLines, metadata: nil)]
             } else {
                 // Render the whole snippet with its explanation content.
                 let docCommentContent = snippetEntity.markup.children.flatMap { self.visit($0) }

Tests/SwiftDocCTests/Rendering/RenderNodeTranslatorTests.swift

@@ -955,7 +955,9 @@ class RenderNodeTranslatorTests: XCTestCase {
             XCTAssertEqual(code.joined(separator: "\n"), """
                 func foo() {}
                 
-                middle()
+                do {
+                  middle()
+                }
                 
                 func bar() {}
                 """)
@@ -987,4 +989,29 @@ class RenderNodeTranslatorTests: XCTestCase {
         XCTAssertEqual(syntax, "swift")
         XCTAssertEqual(code, ["func foo() {}"])
     }
+    
+    func testSnippetSliceTrimsIndentation() throws {
+        let (bundle, context) = try testBundleAndContext(named: "Snippets")
+        let reference = ResolvedTopicReference(bundleIdentifier: bundle.identifier, path: "/documentation/Snippets/SliceIndentation", sourceLanguage: .swift)
+        let article = try XCTUnwrap(context.entity(with: reference).semantic as? Article)
+        var translator = RenderNodeTranslator(context: context, bundle: bundle, identifier: reference, source: nil)
+        let renderNode = try XCTUnwrap(translator.visitArticle(article) as? RenderNode)
+        let discussion = try XCTUnwrap(renderNode.primaryContentSections.first(where: { $0.kind == .content }) as? ContentRenderSection)
+        
+        let lastCodeListingIndex = try XCTUnwrap(discussion.content.indices.last {
+            guard case .codeListing = discussion.content[$0] else {
+                return false
+            }
+            return true
+        })
+
+        guard case let .codeListing(syntax, code, _) = discussion.content[lastCodeListingIndex] else {
+            XCTFail("Missing snippet slice code block")
+            return
+        }
+
+        XCTAssertEqual(syntax, "swift")
+        XCTAssertEqual(code, ["middle()"])
+
+    }
 }

Tests/SwiftDocCTests/Test Bundles/Snippets.docc/SliceIndentation.md

@@ -0,0 +1,27 @@
+# Slice Indentation
+
+This article tests that slices trim extra indentation.
+
+For example, in the following code:
+
+```swift
+do {
+  middle()
+}
+```
+
+Slicing the line which contains `middle()` should look like this:
+
+```swift
+middle()
+```
+
+and not:
+
+```swift
+  middle()
+```
+
+@Snippet(path: "Snippets/Snippets/MySnippet", slice: "middle")
+
+<!-- Copyright (c) 2022 Apple Inc and the Swift Project authors. All Rights Reserved. -->

Tests/SwiftDocCTests/Test Bundles/Snippets.docc/Test-snippets.symbols.json

@@ -30,7 +30,9 @@
         "lines": [
           "func foo() {}",
           "",
-          "middle()",
+          "do {",
+          "  middle()",
+          "}",
           "",
           "func bar() {}"
         ],
@@ -39,9 +41,13 @@
             0,
             1
           ],
+          "middle": [
+            3,
+            4
+          ],
           "bar": [
-            4,
-            5
+            6,
+            7
           ]
         }
       },