Fix compile command stuck in a loop when including multiple custom libraries

legacy/builder/resolve_library.go

@@ -48,7 +48,16 @@ func ResolveLibrary(ctx *types.Context, header string) *libraries.Library {
 
 	selected := resolver.ResolveFor(header, ctx.TargetPlatform.Platform.Architecture)
 	if alreadyImported := importedLibraries.FindByName(selected.Name); alreadyImported != nil {
-		selected = alreadyImported
+		// Certain libraries might have the same name but be different.
+		// This usually happens when the user includes two or more custom libraries that have
+		// different header name but are stored in a parent folder with identical name, like
+		// ./libraries1/Lib/lib1.h and ./libraries2/Lib/lib2.h
+		// Without this check the library resolution would be stuck in a loop.
+		// This behaviour has been reported in this issue:
+		// https://github.com/arduino/arduino-cli/issues/973
+		if selected == alreadyImported {
+			selected = alreadyImported
+		}
 	}
 
 	ctx.LibrariesResolutionResults[header] = types.LibraryResolutionResult{

test/test_compile.py

@@ -564,3 +564,24 @@ def test_compile_with_invalid_url(run_command, data_dir):
     assert "Error creating instance: error loading platform index:" in lines
     expected_index_file = Path(data_dir, "package_example_index.json")
     assert f"loading json index file {expected_index_file}: " + f"open {expected_index_file}:" in lines[-1]
+
+
+def test_compile_with_custom_libraries(run_command, copy_sketch):
+    # Creates config with additional URL to install necessary core
+    url = "http://arduino.esp8266.com/stable/package_esp8266com_index.json"
+    assert run_command(f"config init --dest-dir . --additional-urls {url}")
+
+    # Init the environment explicitly
+    assert run_command("update")
+
+    # Install core to compile
+    assert run_command("core install esp8266:esp8266")
+
+    sketch_path = copy_sketch("sketch_with_multiple_custom_libraries")
+    fqbn = "esp8266:esp8266:nodemcu:xtal=80,vt=heap,eesz=4M1M,wipe=none,baud=115200"
+
+    first_lib = Path(sketch_path, "libraries1")
+    second_lib = Path(sketch_path, "libraries2")
+    # This compile command has been taken from this issue:
+    # https://github.com/arduino/arduino-cli/issues/973
+    assert run_command(f"compile --libraries {first_lib},{second_lib} -b {fqbn} {sketch_path}")