Bug 1321292 - mozboot: Don't suggest non-existent .cargo.env. r=gps

On Windows, the rustup installer doesn't create ~/.cargo/env
but instead pokes .cargo/bin into the path in the Windows
registry. This doesn't necessarily propagate to the msys
evironment however, so some PATH manipulation may still
be necessary.

Split our path advice to be clear in both the new install
and unconfigured path cases, and amend our path update
advice to not mention .cargo/env if it isn't present.

MozReview-Commit-ID: 9IHhS6UYCqq

--HG--
extra : rebase_source : 898615106078882f335385ac0b50eff1612377f0

python/mozboot/mozboot/base.py

@@ -73,16 +73,33 @@ We recommend the following tools for installing Python:
     official installers -- http://www.python.org/
 '''
 
+RUST_INSTALL_COMPLETE = '''
+Rust installation complete. You should now have rustc and cargo
+in %(cargo_bin)s
+
+The installer tries to add these to your default shell PATH, so
+restarting your shell and running this script again may work.
+If it doesn't, you'll need to add the new command location
+manually.
+
+If restarting doesn't work, edit your shell initialization
+script, which may be called ~/.bashrc or ~/.bash_profile or
+~/.profile, and add the following line:
+
+    %(cmd)s
+
+Then restart your shell and run the bootstrap script again.
+'''
+
 RUST_NOT_IN_PATH = '''
-You have some rust files in %(cargo_bin)s, but they're not part of the
-standard PATH.'''
+You have some rust files in %(cargo_bin)s
+but they're not part of this shell's PATH.
 
-RUST_PATH_ADVICE = '''
-To make these available, please add this directory to the PATH variable
-in your shell initialization script, which may be called ~/.bashrc or
-~/.bash_profile or ~/.profile. Edit this and add the following line:
+To add these to the PATH, edit your shell initialization
+script, which may be called ~/.bashrc or ~/.bash_profile or
+~/.profile, and add the following line:
 
-    source %(cargo_home)s/env
+    %(cmd)s
 
 Then restart your shell and run the bootstrap script again.
 '''
@@ -108,8 +125,7 @@ run this bootstrapper again.
 
 If this continues to fail and you are sure you have a modern Rust on your
 system, ensure it is on the $PATH and try again. If that fails, you'll need to
-install Rust manually and ensure the path with the rustc and cargo  binaries
-are listed in the $PATH environment variable.
+install Rust manually.
 
 We recommend the installer from https://rustup.rs/ for installing Rust,
 but you may be able to get a recent enough version from a software install
@@ -521,6 +537,21 @@ class BaseBootstrapper(object):
         cargo_bin = os.path.join(cargo_home, 'bin')
         return cargo_home, cargo_bin
 
+    def print_rust_path_advice(self, template, cargo_home, cargo_bin):
+        # Suggest ~/.cargo/env if it exists.
+        if os.path.exists(os.path.join(cargo_home, 'env')):
+            cmd = 'source %s/env' % cargo_home
+        else:
+            # On Windows rustup doesn't write out ~/.cargo/env
+            # so fall back to a manual PATH update. Bootstrap
+            # only runs under msys, so a unix-style shell command
+            # is appropriate there.
+            cmd = 'export PATH=%s:$PATH' % cargo_bin
+        print(template % {
+            'cargo_bin': cargo_bin,
+            'cmd': cmd,
+        })
+
     def ensure_rust_modern(self):
         modern, version = self.is_rust_modern()
 
@@ -536,11 +567,11 @@ class BaseBootstrapper(object):
             have_rustc = os.path.exists(try_rustc)
             have_cargo = os.path.exists(try_cargo)
             if have_rustc or have_cargo:
-                print(RUST_NOT_IN_PATH % { 'cargo_bin': cargo_bin })
-                print(RUST_PATH_ADVICE % { 'cargo_home': cargo_home })
+                self.print_rust_path_advice(RUST_NOT_IN_PATH,
+                        cargo_home, cargo_bin)
                 sys.exit(1)
-
-        print('Your version of Rust (%s) is too old.' % version)
+        else:
+            print('Your version of Rust (%s) is too old.' % version)
 
         rustup = self.which('rustup')
         if rustup:
@@ -591,9 +622,8 @@ class BaseBootstrapper(object):
                 '--default-host', platform,
             ])
             cargo_home, cargo_bin = self.cargo_home()
-            print('Rust installation complete.')
-            print('You should now have rustc and cargo in %s' % cargo_bin)
-            print(RUST_PATH_ADVICE % { 'cargo_home': cargo_home })
+            self.print_rust_path_advice(RUST_INSTALL_COMPLETE,
+                    cargo_home, cargo_bin)
         finally:
             try:
                 os.remove(rustup_init)