Allow overriding the number of columns with ALCOTEST_COLUMNS env var

CHANGES.md

@@ -1,5 +1,15 @@
 ### unreleased
 
+- Fix division by zero when size of the terminal is incorrectly
+  reported as zero. (fix #356, #381, @MisterDA)
+
+- Enable terminal size reporting on macOS and Windows. Also report the
+  terminal size even when the test is run buffered by Dune.
+  (#381, @MisterDA)
+
+- Allow overriding the number of columns with `ALCOTEST_COLUMNS` env
+  var. (#322, #381, @MisterDA)
+
 ### 1.7.0 (2023-02-24)
 
 - Allow skipping a test case from inside the test case (#368, @apeschar)

alcotest-help.txt

@@ -77,6 +77,11 @@ ENVIRONMENT
        ALCOTEST_COLOR
            See option --color.
 
+       ALCOTEST_COLUMNS
+           Number of columns after which Alcotest truncates or splits written
+           lines. Default is to auto-detect using the terminal's dimensions,
+           or fallback to 80 columns.
+
        ALCOTEST_COMPACT
            See option --compact.
 

src/alcotest-engine/cli.ml

@@ -69,8 +69,22 @@ module Make (P : Platform.MAKER) (M : Monad.S) :
     in
     Cmdliner.Cmd.Env.info "ALCOTEST_SOURCE_CODE_POSITION" ~doc
 
+  let alcotest_columns =
+    let doc =
+      "Number of columns after which Alcotest truncates or splits written \
+       lines. Default is to auto-detect using the terminal's dimensions, or \
+       fallback to 80 columns."
+    in
+    Cmdliner.Cmd.Env.info "ALCOTEST_COLUMNS" ~doc
+
   let envs =
-    [ ci_env; github_action_env; ocamlci_env; alcotest_source_code_position ]
+    [
+      ci_env;
+      github_action_env;
+      ocamlci_env;
+      alcotest_source_code_position;
+      alcotest_columns;
+    ]
 
   let set_color =
     let env = Cmd.Env.info "ALCOTEST_COLOR" in

src/alcotest/alcotest.ml

@@ -74,9 +74,13 @@ module Unix_platform (M : Alcotest_engine.Monad.S) = struct
   let stdout_isatty () = Unix.(isatty stdout)
 
   let stdout_columns () =
-    match Terminal.get_dimensions () with
-    | Some { columns; _ } when columns > 0 -> Some columns
-    | _ -> None
+    let bind o f = match o with Some o -> f o | None -> None in
+    match bind (Sys.getenv_opt "ALCOTEST_COLUMNS") int_of_string_opt with
+    | Some columns when columns > 0 -> Some columns
+    | _ -> (
+        match Terminal.get_dimensions () with
+        | Some { columns; _ } when columns > 0 -> Some columns
+        | _ -> None)
 
   external before_test :
     output:out_channel -> stdout:out_channel -> stderr:out_channel -> unit

test/e2e/dune

@@ -4,7 +4,9 @@
    ; Don't run tests as if Alcotest was run in CI
    (CI false)
    ; Don't guess source code position for compat with < 4.12.
-   (ALCOTEST_SOURCE_CODE_POSITION false))))
+   (ALCOTEST_SOURCE_CODE_POSITION false)
+   ; Set to 80 columns for output reproducibility
+   (ALCOTEST_COLUMNS 80))))
 
 (executable
  (name gen_dune_rules)