Bugfix: exception when trying to select a tool without the assistant …

…while the configured one is missing (#1551)

* Fix exception when trying to select a toolchain

This problem arised only if trying to select a toolchain with --select <tool>
while the configured tool was missing on disk.

* Test for fix

src/alire/alire-solutions-diffs.adb

@@ -431,7 +431,10 @@ package body Alire.Solutions.Diffs is
               and then Toolchains.Tool_Is_Configured (GNAT_Crate)
               and then Toolchains.Tool_Milestone (GNAT_Crate).Crate
                        = GNAT_External_Crate
-              and then not Toolchains.Tool_Release (GNAT_Crate).Satisfies (Dep)
+              and then
+                (Toolchains.Tool_Is_Missing (GNAT_Crate)
+                 or else
+                   not Toolchains.Tool_Release (GNAT_Crate).Satisfies (Dep))
             then
                Trace.Log (Prefix, Level);
                Trace.Log (Prefix & Icon (Missing)

src/alire/alire-toolchains.adb

@@ -632,6 +632,34 @@ package body Alire.Toolchains is
       Put_Info (Release.Milestone.TTY_Image & " installed successfully.");
    end Deploy;
 
+   --------------------
+   -- Deploy_Missing --
+   --------------------
+
+   procedure Deploy_Missing is
+   begin
+      for Tool of Tools loop
+         if Tool_Is_Configured (Tool) and then Tool_Is_Missing (Tool) then
+            declare
+               Mil : constant Milestones.Milestone := Tool_Milestone (Tool);
+            begin
+               Put_Warning ("Tool " & Mil.TTY_Image
+                            & " is missing, redeploying...");
+               if Index.Exists (Mil.Crate, Mil.Version) then
+                  Deploy (Index.Find (Mil.Crate, Mil.Version));
+               else
+                  Raise_Checked_Error
+                    (Errors.Wrap
+                       ("A configured tool is missing on disk and unavailable "
+                        & "in the loaded index.",
+                        " Run " & TTY.Terminal ("alr toolchain --select")
+                        & " to select another toolchain"));
+               end if;
+            end;
+         end if;
+      end loop;
+   end Deploy_Missing;
+
    ------------
    -- Remove --
    ------------
@@ -725,4 +753,15 @@ package body Alire.Toolchains is
       raise Constraint_Error with "Not installed: " & Target.TTY_Image;
    end Release;
 
+   ---------------------
+   -- Tool_Is_Missing --
+   ---------------------
+
+   function Tool_Is_Missing (Crate : Crate_Name) return Boolean is
+   begin
+      return not (for some Release of Available (Detect_Externals =>
+                                                   Tool_Is_External (Crate))
+                  => Release.Milestone = Tool_Milestone (Crate));
+   end Tool_Is_Missing;
+
 end Alire.Toolchains;

src/alire/alire-toolchains.ads

@@ -71,6 +71,10 @@ package Alire.Toolchains is
    --  Use the stored config to check if the tool is external without having to
    --  detect it. Defaults to True if unset or tool is not configured.
 
+   function Tool_Is_Missing (Crate : Crate_Name) return Boolean
+     with Pre => Tool_Is_Configured (Crate);
+   --  Says is the configured tool is not ready for use and must be downloaded
+
    function Tool_Milestone (Crate : Crate_Name) return Milestones.Milestone;
 
    function Tool_Release (Crate : Crate_Name) return Releases.Release;
@@ -132,6 +136,9 @@ package Alire.Toolchains is
                      Location : Any_Path := Path);
    --  Deploy a release in the specified location
 
+   procedure Deploy_Missing;
+   --  Deploy any configured tool that is not found where expected on disk
+
    procedure Remove
      (Release : Releases.Release;
       Confirm : Boolean := not CLIC.User_Input.Not_Interactive)

src/alr/alr-commands-toolchain.adb

@@ -124,6 +124,7 @@ package body Alr.Commands.Toolchain is
             --  command-line, will impose an origin compatibility constraint
 
             if Toolchains.Tool_Is_Configured (Tool)
+              and then not Toolchains.Tool_Is_Missing (Tool)
               and then not
                 (for some P of Pending =>
                    Toolchains.Tool_Release (Tool).Provides (P) or else

testsuite/tests/toolchain/select-while-missing/test.py

@@ -0,0 +1,18 @@
+"""
+Check a particular error in which selecting a compiler via `alr toolchain
+--select <compiler>` fails if the previously configured compiler is missing on
+disk.
+"""
+
+from drivers.alr import run_alr
+
+# Configure a valid compiler
+run_alr("toolchain", "--select", "gnat_native", "gprbuild")
+
+# Configure an invalid compiler
+run_alr("config", "--global", "--set", "toolchain.use.gnat", "gnat_nono=1.2.3")
+
+# This must succeed
+run_alr("toolchain", "--select", "gnat_native=1.0")
+
+print("SUCCESS")

testsuite/tests/toolchain/select-while-missing/test.yaml

@@ -0,0 +1,4 @@
+driver: python-script
+build_mode: both
+indexes:
+    gnat_toolchain_index: {}