Don't run Powershell in a dumb terminal (fix #110)

src/steps/os/windows.rs

@@ -1,6 +1,6 @@
 use crate::error::Error;
 use crate::executor::{CommandExt, RunType};
-use crate::terminal::print_separator;
+use crate::terminal::{is_dumb, print_separator};
 use crate::utils::{self, which};
 use log::error;
 use std::path::PathBuf;
@@ -46,9 +46,13 @@ pub struct Powershell {
 }
 
 impl Powershell {
+    /// Returns a powershell instance.
+    ///
+    /// If the powershell binary is not found, or the current terminal is dumb
+    /// then the instance of this struct will skip all the powershell steps.
     pub fn new() -> Self {
         Powershell {
-            path: which("powershell"),
+            path: which("powershell").filter(|_| !is_dumb()),
         }
     }
 

src/terminal.rs

@@ -126,3 +126,8 @@ pub fn print_warning<P: AsRef<str>>(message: P) {
 pub fn print_result<P: AsRef<str>>(key: P, succeeded: bool) {
     TERMINAL.lock().unwrap().print_result(key, succeeded)
 }
+
+/// Tells whether the terminal is dumb.
+pub fn is_dumb() -> bool {
+    TERMINAL.lock().unwrap().width.is_none()
+}