Revert "improve heuristics for @main support (#5678) (#5680)" (#5684)

Author: shahmishal

Sources/Build/BuildPlan.swift

@@ -626,26 +626,21 @@ public final class SwiftTargetBuildDescription {
     public let isTestDiscoveryTarget: Bool
 
     /// True if this module needs to be parsed as a library based on the target type and the configuration
-    /// of the source code
+    /// of the source code (for example because it has a single source file whose name isn't "main.swift").
+    /// This deactivates heuristics in the Swift compiler that treats single-file modules and source files
+    /// named "main.swift" specially w.r.t. whether they can have an entry point.
+    ///
+    /// See https://bugs.swift.org/browse/SR-14488 for discussion about improvements so that SwiftPM can
+    /// convey the intent to build an executable module to the compiler regardless of the number of files
+    /// in the module or their names.
     var needsToBeParsedAsLibrary: Bool {
-        switch self.target.type {
+        switch target.type {
         case .library, .test:
             return true
         case .executable:
-            // This deactivates heuristics in the Swift compiler that treats single-file modules and source files
-            // named "main.swift" specially w.r.t. whether they can have an entry point.
-            //
-            // See https://bugs.swift.org/browse/SR-14488 for discussion about improvements so that SwiftPM can
-            // convey the intent to build an executable module to the compiler regardless of the number of files
-            // in the module or their names.
-            if self.toolsVersion < .v5_5 || self.sources.count != 1 {
-                return false
-            }
-            // looking into the file content to see if it is using the @main annotation which requires parse-as-library
-            // this is not bullet-proof since theoretically the file can contain the @main string for other reasons
-            // but it is the closest to accurate we can do at this point
-            let content: String = self.sources.first.flatMap({ try? self.fileSystem.readFileContents($0) }) ?? ""
-            return content.contains("@main")
+            guard toolsVersion >= .v5_5 else { return false }
+            let sources = self.sources
+            return sources.count == 1 && sources.first?.basename != "main.swift"
         default:
             return false
         }

Tests/BuildTests/BuildPlanTests.swift

@@ -1014,41 +1014,15 @@ final class BuildPlanTests: XCTestCase {
 
     func testParseAsLibraryFlagForExe() throws {
         let fs = InMemoryFileSystem(emptyFiles:
-            // executable has a single source file not named `main.swift`, without @main.
+            // First executable has a single source file not named `main.swift`.
             "/Pkg/Sources/exe1/foo.swift",
-            // executable has a single source file named `main.swift`, without @main.
+            // Second executable has a single source file named `main.swift`.
             "/Pkg/Sources/exe2/main.swift",
-            // executable has a single source file not named `main.swift`, with @main.
-            "/Pkg/Sources/exe3/foo.swift",
-            // executable has a single source file named `main.swift`, with @main
-            "/Pkg/Sources/exe4/main.swift",
-            // executable has multiple source files.
-            "/Pkg/Sources/exe5/bar.swift",
-            "/Pkg/Sources/exe5/main.swift"
+            // Third executable has multiple source files.
+            "/Pkg/Sources/exe3/bar.swift",
+            "/Pkg/Sources/exe3/main.swift"
         )
 
-        try fs.writeFileContents(AbsolutePath("/Pkg/Sources/exe3/foo.swift")) {
-            """
-            @main
-            struct Runner {
-              static func main() {
-                print("hello world")
-              }
-            }
-            """
-        }
-
-        try fs.writeFileContents(AbsolutePath("/Pkg/Sources/exe4/main.swift")) {
-            """
-            @main
-            struct Runner {
-              static func main() {
-                print("hello world")
-              }
-            }
-            """
-        }
-
         let observability = ObservabilitySystem.makeForTesting()
         let graph = try loadPackageGraph(
             fileSystem: fs,
@@ -1061,8 +1035,6 @@ final class BuildPlanTests: XCTestCase {
                         TargetDescription(name: "exe1", type: .executable),
                         TargetDescription(name: "exe2", type: .executable),
                         TargetDescription(name: "exe3", type: .executable),
-                        TargetDescription(name: "exe4", type: .executable),
-                        TargetDescription(name: "exe5", type: .executable),
                     ]),
             ],
             observabilityScope: observability.topScope
@@ -1076,30 +1048,22 @@ final class BuildPlanTests: XCTestCase {
             observabilityScope: observability.topScope
         ))
 
-        result.checkProductsCount(5)
-        result.checkTargetsCount(5)
+        result.checkProductsCount(3)
+        result.checkTargetsCount(3)
 
         XCTAssertNoDiagnostics(observability.diagnostics)
 
-        // single source file not named main, and without @main should not have -parse-as-library.
+        // Check that the first target (single source file not named main) has -parse-as-library.
         let exe1 = try result.target(for: "exe1").swiftTarget().emitCommandLine()
-        XCTAssertNoMatch(exe1, ["-parse-as-library"])
+        XCTAssertMatch(exe1, ["-parse-as-library"])
 
-         // single source file named main, and without @main should not have -parse-as-library.
+        // Check that the second target (single source file named main) does not have -parse-as-library.
         let exe2 = try result.target(for: "exe2").swiftTarget().emitCommandLine()
         XCTAssertNoMatch(exe2, ["-parse-as-library"])
 
-        // single source file not named main, with @main should have -parse-as-library.
+        // Check that the third target (multiple source files) does not have -parse-as-library.
         let exe3 = try result.target(for: "exe3").swiftTarget().emitCommandLine()
-        XCTAssertMatch(exe3, ["-parse-as-library"])
-
-        // single source file named main, with @main should have -parse-as-library.
-        let exe4 = try result.target(for: "exe4").swiftTarget().emitCommandLine()
-        XCTAssertMatch(exe4, ["-parse-as-library"])
-
-        // multiple source files should not have -parse-as-library.
-        let exe5 = try result.target(for: "exe5").swiftTarget().emitCommandLine()
-        XCTAssertNoMatch(exe5, ["-parse-as-library"])
+        XCTAssertNoMatch(exe3, ["-parse-as-library"])
     }
 
     func testCModule() throws {