engine.#Source: Fix relative path support

Fixes #1492

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

tests/tasks/source/source.cue

@@ -24,19 +24,19 @@ engine.#Plan & {
 		}
 
 		verifyHello: engine.#ReadFile & {
-			input: source.output
-			path:  "/hello.txt"
-		} & {
-			// assert result
-			contents: "hello\n"
-		}
-
-		verifyWorld: engine.#ReadFile & {
 			input: source.output
 			path:  "/world.txt"
 		} & {
 			// assert result
 			contents: "world\n"
 		}
+
+		verifyWorld: engine.#ReadFile & {
+			input: exec.output
+			path:  "/test.txt"
+		} & {
+			// assert result
+			contents: "hello world"
+		}
 	}
 }

tests/tasks/source/source_invalid_path.cue

@@ -11,7 +11,7 @@ engine.#Plan & {
 		}
 
 		source: engine.#Source & {
-			path: ".."
+			path: "testdata/../.."
 		}
 	}
 }

tests/tasks/source/source_relative.cue

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"dagger.io/dagger/engine"
+)
+
+engine.#Plan & {
+	actions: {
+		image: engine.#Pull & {
+			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
+		}
+
+		source: engine.#Source & {
+			path: "./testdata"
+		}
+
+		verifyHello: engine.#ReadFile & {
+			input: source.output
+			path:  "/world.txt"
+		} & {
+			// assert result
+			contents: "world\n"
+		}
+	}
+}

tests/tasks/source/testdata/world.txt

@@ -0,0 +1 @@
+world