fetch: add --all-platforms switch

- Iterate `[:macos, :linux] × [:intel, :arm]` (4 combos) for verifying
  multi-platform cask URLs and checksums in a single command, instead
  of `--os=all --arch=all` which iterates every macOS codename.
- Tolerate `CaskInvalidError`/`CaskUnreadableError` during multi-combo
  fetches for casks that legitimately omit some platforms (mirrors the
  `bump-cask-pr.rb` rescue pattern).

Author: p-linnane

Library/Homebrew/cli/args.rb

@@ -126,6 +126,8 @@ def only_formula_or_cask
 
       sig { returns(T::Array[[Symbol, Symbol]]) }
       def os_arch_combinations
+        return OnSystem::BASE_OS_OPTIONS.product(OnSystem::ARCH_OPTIONS) if @table[:all_platforms?]
+
         skip_invalid_combinations = false
 
         oses = case (os_sym = @table[:os]&.to_sym)

Library/Homebrew/cmd/fetch.rb

@@ -25,6 +25,8 @@ class FetchCmd < AbstractCommand
         flag   "--arch=",
                description: "Download for the given CPU architecture. " \
                             "(Pass `all` to download for all architectures.)"
+        switch "--all-platforms",
+               description: "Download for every supported OS and CPU architecture combination."
         flag   "--bottle-tag=",
                description: "Download a bottle for given tag."
         switch "--HEAD",
@@ -65,6 +67,9 @@ class FetchCmd < AbstractCommand
         conflicts "--formula", "--cask"
         conflicts "--os", "--bottle-tag"
         conflicts "--arch", "--bottle-tag"
+        conflicts "--all-platforms", "--os"
+        conflicts "--all-platforms", "--arch"
+        conflicts "--all-platforms", "--bottle-tag"
 
         named_args [:formula, :cask], min: 1
       end
@@ -160,9 +165,13 @@ def run
 
             os_arch_combinations.each do |os, arch|
               SimulateSystem.with(os:, arch:) do
-                cask = Cask::CaskLoader.load(ref)
+                loaded_cask = begin
+                  Cask::CaskLoader.load(ref)
+                rescue Cask::CaskInvalidError, Cask::CaskUnreadableError
+                  raise unless cask.on_system_blocks_exist?
+                end
 
-                if cask.url.nil? || cask.sha256.nil?
+                if loaded_cask.nil? || loaded_cask.url.nil? || loaded_cask.sha256.nil?
                   opoo "Cask #{cask} is not supported on os #{os} and arch #{arch}"
                   next
                 end
@@ -171,7 +180,7 @@ def run
                 quarantine = true if quarantine.nil?
 
                 download = Cask::Download.new(
-                  cask,
+                  loaded_cask,
                   quarantine:,
                   require_sha: Homebrew::EnvConfig.cask_opts_require_sha?,
                 )