Merge pull request #115 from joewreschnig/autopath

Automatically detect the path of `clangd`, `arduino-cli`, and its configuration

Author: cmaglie

Diff for: README.md

@@ -70,7 +70,7 @@ The prerequisites to run the Arduino Language Server are:
 - [Arduino CLI](https://github.com/arduino/arduino-cli)
 - [clangd](https://github.com/clangd/clangd/releases)
 
-To start the language server the IDE must provide the path to Arduino CLI and clangd with the following flags in addition to the target board FQBN:
+To start the language server the IDE may provide the path to Arduino CLI and clangd with the following flags in addition to the target board FQBN:
 
 ```
 ./arduino-language-server \

Diff for: main.go

@@ -7,7 +7,10 @@ import (
 	"net/http"
 	_ "net/http/pprof"
 	"os"
+	"os/exec"
 	"os/signal"
+	"os/user"
+	"path"
 
 	"github.com/arduino/arduino-language-server/ls"
 	"github.com/arduino/arduino-language-server/streams"
@@ -68,15 +71,41 @@ func main() {
 		log.SetOutput(os.Stderr)
 	}
 
-	if *cliPath != "" {
+	if *cliDaemonAddress != "" || *cliDaemonInstanceNumber != -1 {
+		// if one is set, both must be set
+		if *cliDaemonAddress == "" || *cliDaemonInstanceNumber == -1 {
+			log.Fatal("ArduinoCLI daemon address and instance number must be set.")
+		}
+	} else {
+		if *cliConfigPath == "" {
+			if user, _ := user.Current(); user != nil {
+				candidate := path.Join(user.HomeDir, ".arduino15/arduino-cli.yaml")
+				if _, err := os.Stat(candidate); err == nil {
+					*cliConfigPath = candidate
+					log.Printf("ArduinoCLI config file found at %s\n", candidate)
+				}
+			}
+		}
 		if *cliConfigPath == "" {
 			log.Fatal("Path to ArduinoCLI config file must be set.")
 		}
-	} else if *cliDaemonAddress == "" || *cliDaemonInstanceNumber == -1 {
-		log.Fatal("ArduinoCLI daemon address and instance number must be set.")
+		if *cliPath == "" {
+			bin, _ := exec.LookPath("arduino-cli")
+			if bin == "" {
+				log.Fatal("Path to ArduinoCLI must be set.")
+			}
+			log.Printf("arduino-cli found at %s\n", bin)
+			*cliPath = bin
+		}
 	}
+
 	if *clangdPath == "" {
-		log.Fatal("Path to Clangd must be set.")
+		bin, _ := exec.LookPath("clangd")
+		if bin == "" {
+			log.Fatal("Path to Clangd must be set.")
+		}
+		log.Printf("clangd found at %s\n", bin)
+		*clangdPath = bin
 	}
 
 	config := &ls.Config{