fix: avoid spurious blank line on alr exec when ANSI enabled

.vscode/launch.json

@@ -25,12 +25,17 @@
             "justMyCode": false
         },
         {
-            "name": "(gdb) Launch alr at /tmp/a/xxx",
+            "name": "Alire: debug ./bin/alr at /tmp/a/xxx",
             "type": "cppdbg",
             "request": "launch",
             "program": "${workspaceFolder}/bin/alr",
-            "args": ["-d", "-vv", "with", "libfoo"],
-            "stopAtEntry": true,
+            "args": [
+                "exec",
+                "--",
+                "echo",
+                "blah"
+            ],
+            "stopAtEntry": false,
             "cwd": "/tmp/a/xxx",
             "environment": [],
             "externalConsole": false,
@@ -42,11 +47,11 @@
                     "ignoreFailures": true
                 },
                 {
-                    "description": "Set Disassembly Flavor to Intel",
-                    "text": "-gdb-set disassembly-flavor intel",
+                    "description": "Disable questions on multiple matches",
+                    "text": "set multiple-symbols cancel",
                     "ignoreFailures": true
                 }
             ]
         }
     ]
-}
+}

src/alire/alire-os_lib-subprocess.adb

@@ -6,6 +6,7 @@ with AnsiAda; use AnsiAda;
 
 with CLIC.TTY;
 
+with GNAT.IO;
 with GNAT.OS_Lib;
 
 package body Alire.OS_Lib.Subprocess is
@@ -208,7 +209,13 @@ package body Alire.OS_Lib.Subprocess is
             and then CLIC.TTY.Is_TTY
             and then CLIC.TTY.Color_Enabled
          then
-            Ada.Text_IO.Put (Style (Dim, State));
+            --  We cannot use Ada.Text_IO here, as it mandates endlines,
+            --  and the Ada runtime flushes this with an extra '\n' on
+            --  finalization if this is the last output, creating an extra
+            --  empty line in e.g. `alr exec echo whatever`. GNAT.IO is
+            --  uncooked so it works as expected.
+            Ada.Text_IO.Flush; -- So we don't mix bufferings
+            GNAT.IO.Put (Style (Dim, State));
          end if;
       end Dim;
 

src/alr/alr-commands-exec.adb

@@ -18,7 +18,6 @@ package body Alr.Commands.Exec is
       use GNAT.Strings;
       use Ada.Containers;
       use AAA.Strings;
-
    begin
       Cmd.Forbids_Structured_Output;
 

src/alr/alr-utils-temp_file.adb

@@ -12,9 +12,7 @@ package body Alr.Utils.Temp_File is
    begin
       if Exists (This.Name) then
          Delete_File (This.Name);
-         null;
       end if;
-
    exception
       when E : others =>
          Alire.Utils.Finalize_Exception (E);

testsuite/tests/exec/no-extra-line/test.py

@@ -0,0 +1,19 @@
+"""
+Check that `alr exec` does not add an extra line at the end of the output.
+Fix for issue #2004. This test is more or less moot, since the bug can only be
+observed when running interactively with ANSI coloring, which is disabled in
+the testsuite and cannot be forced on. At least, it checks that no extra line is
+added in the non-interactive case.
+"""
+
+from drivers.alr import run_alr, init_local_crate
+from drivers.asserts import assert_eq
+
+# Initialize a crate, enter it, and run an echo through exec. Check the output.
+
+init_local_crate()
+
+p = run_alr("exec", "--", "echo", "HELLO", quiet=False)
+assert_eq("HELLO\n", p.out)  # Note: only one newline at the end
+
+print("SUCCESS")

testsuite/tests/exec/no-extra-line/test.yaml

@@ -0,0 +1,3 @@
+driver: python-script
+indexes:
+    compiler_only_index: {}