From 14fd7d93ca5e9f19eec3aecd55fea3b62ad9fe3c Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Tue, 21 Jul 2020 19:36:58 +0300
Subject: [PATCH] v.pref: fix `v build file.v`

---
 cmd/v/help/default.txt |  2 +-
 cmd/v/v.v              |  2 +-
 vlib/v/pref/pref.v     | 15 +++++++++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/cmd/v/help/default.txt b/cmd/v/help/default.txt
index fea94b43de..ec9ed94674 100644
--- a/cmd/v/help/default.txt
+++ b/cmd/v/help/default.txt
@@ -34,7 +34,7 @@ V supports the following commands:
    list              List all installed modules.
    outdated          Show installed modules that need updates.
 * Others:
-   build             Build a V code in the provided path (the default, so you can skip the word `build`).
+   build             Build V code in the provided path (the default, so you can skip the word `build`).
    translate         Translate C code to V (coming soon in 0.3).
    tracev            Produce a tracing version of the v compiler.
                      Use `tracev yourfile.v` when the compiler panics.
diff --git a/cmd/v/v.v b/cmd/v/v.v
index f4c73f1569..05bab6ad8a 100644
--- a/cmd/v/v.v
+++ b/cmd/v/v.v
@@ -87,7 +87,7 @@ fn main() {
 		}
 		else {}
 	}
-	if command in ['run', 'build-module'] || command.ends_with('.v') || os.exists(command) {
+	if command in ['run', 'build', 'build-module'] || command.ends_with('.v') || os.exists(command) {
 		// println('command')
 		// println(prefs.path)
 		builder.compile(command, prefs)
diff --git a/vlib/v/pref/pref.v b/vlib/v/pref/pref.v
index b2ce95bfe5..5b382995aa 100644
--- a/vlib/v/pref/pref.v
+++ b/vlib/v/pref/pref.v
@@ -310,6 +310,13 @@ pub fn parse_args(args []string) (&Preferences, string) {
 	}
 	if command.ends_with('.v') || os.exists(command) {
 		res.path = command
+	} else if command == 'build' {
+		if command_pos + 2 != args.len {
+			eprintln('`v build` requires exactly one argument - either a single .v file, or a single folder/ containing several .v files')
+			exit(1)
+		}
+		res.path = args[command_pos + 1]
+		must_exist(res.path)
 	} else if command == 'run' {
 		res.is_run = true
 		if command_pos + 2 > args.len {
@@ -318,6 +325,7 @@ pub fn parse_args(args []string) (&Preferences, string) {
 		}
 		res.path = args[command_pos + 1]
 		res.run_args = args[command_pos + 2..]
+		must_exist(res.path)
 	}
 	if command == 'build-module' {
 		res.build_mode = .build_module
@@ -327,6 +335,13 @@ pub fn parse_args(args []string) (&Preferences, string) {
 	return res, command
 }
 
+fn must_exist(path string) {
+	if !os.exists(path) {
+		eprintln('v expects that `$path` exists, but it does not')
+		exit(1)
+	}        
+}
+
 pub fn backend_from_string(s string) ?Backend {
 	match s {
 		'c' { return .c }