Add export method for overriding environment

Sources/DotEnvy/Documentation.docc/Documentation.md

@@ -80,6 +80,17 @@ func env() -> [String: String] {
 }
 ```
 
+If you want to override the process environment, you can use ``DotEnvironment/export(overwrite:)``:
+
+```swift
+import DotEnvy
+
+func overrideEnv() throws {
+    let environment = try DotEnvironment.make()
+    environment.export()
+}
+```
+
 ## Topics
 
 ### Group

Sources/DotEnvy/Load.swift

@@ -46,6 +46,16 @@ extension DotEnvironment.Override {
 }
 
 extension DotEnvironment {
+    /// Export the `DotEnvironment` values into the process environment.
+    ///
+    /// - Parameter overwrite: Indicates if the calculated value should overwrite any existing value
+    ///                        in the process environment.
+    public func export(overwrite: Bool = true) {
+        for value in self.merge() {
+            setenv(value.key, value.value, overwrite ? 1 : 0)
+        }
+    }
+
     /// Load the contents of a dotenv file into a dictionary.
     ///
     /// Defaults to loading `.env` from the current working directory. If the file does not exist, an
@@ -77,6 +87,21 @@ extension DotEnvironment {
         }
     }
 
+    /// Create a `DotEnvironment` from `source` and `overrides`.
+    ///
+    /// - Parameter source: A string in dotenv format.
+    public static func make(
+        source: String,
+        overrides: DotEnvironment.Override = .process
+    ) throws -> DotEnvironment {
+        do {
+            let values = try self.parse(string: source)
+            return DotEnvironment(environment: values, overrides: overrides)
+        } catch let error as ParseErrorWithLocation {
+            throw LoadError.parseError(error, source)
+        }
+    }
+
     /// Create a `DotEnvironment` from `url` and `overrides`.
     ///
     /// Defaults to loading `.env` from the current working directory and using the process environment

Tests/DotEnvyTests/ExportTests.swift

@@ -0,0 +1,32 @@
+@testable import DotEnvy
+import XCTest
+
+final class ExportTests: XCTestCase {
+    func testOverwrite() throws {
+        setenv("KEY1", "ENVVALUE1", 1)
+        let dotenv = try DotEnvironment.make(
+            source: """
+            KEY1=DOTENVVALUE1
+            KEY2=DOTENVVALUE2
+            """,
+            overrides: .none
+        )
+        dotenv.export(overwrite: true)
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY1"], "DOTENVVALUE1")
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY2"], "DOTENVVALUE2")
+    }
+
+    func testNoOverwrite() throws {
+        setenv("KEY1", "ENVVALUE1", 1)
+        let dotenv = try DotEnvironment.make(
+            source: """
+            KEY1=DOTENVVALUE1
+            KEY2=DOTENVVALUE2
+            """,
+            overrides: .none
+        )
+        dotenv.export(overwrite: false)
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY1"], "ENVVALUE1")
+        XCTAssertEqual(ProcessInfo.processInfo.environment["KEY2"], "DOTENVVALUE2")
+    }
+}

Tests/DotEnvyTests/LoadTests.swift

@@ -59,6 +59,25 @@ final class LoadTests: XCTestCase {
         }
     }
 
+    func testLoadErrorFromMakeSource() throws {
+        let source = """
+        KEY1=VALUE1
+        KEY2-VALUE2
+        KEY3=VALUE3
+        """
+        XCTAssertThrowsError(try DotEnvironment.make(source: source)) { error in
+            guard let error = error as? LoadError else {
+                XCTFail("Unexpected error: \(error)")
+                return
+            }
+            guard case let .parseError(p, _) = error else {
+                XCTFail("Unexpected LoadError: \(error)")
+                return
+            }
+            XCTAssertEqual(p.error, .missingEquals)
+        }
+    }
+
     func testMakeDotEnvironmentWithDefaultFile() throws {
         try inTemporaryDirectory { tempDir in
             try Data("""