fix(strategies): shorten parametric struct option values in show output

Generalize `_display_value` to detect any option value whose type is a
parametric struct (e.g. an OrdinaryDiffEq algorithm instance) and display
just its type name, instead of hardcoding the `:alg` option name. Standard
containers (Array, Tuple, NamedTuple, Dict) are excluded and keep showing
their full contents. Also fixes a latent bug where a simple Symbol/String
`:alg` value would have displayed as "Symbol" instead of its real value.

Bump to 0.28.6-beta, update CHANGELOG.md and BREAKING.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: ocots

BREAKING.md

@@ -3,6 +3,22 @@
 
 This document outlines all breaking changes introduced in CTBase v0.18.0-beta compared to v0.17.4. Use this guide to migrate your code and understand the impact of these changes.
 
+## Non-breaking note (0.28.6-beta)
+
+- **`Strategies`: option values whose type is a parametric struct are now
+  displayed by type name only, instead of their full `repr`.** In
+  `Base.show(io, MIME"text/plain", strategy)`, `Base.show(io, strategy)`,
+  and the equivalent `StrategyOptions` show methods, a value like an
+  `OrdinaryDiffEq` algorithm instance (e.g. `Vern6{typeof(trivial_limiter!),
+  ...}(...)`) previously printed its entire type-parameterized `repr`,
+  making the tree display unreadable. It now prints just the type name
+  (e.g. `Vern6`). The rule applies to **any** option value whose type is a
+  parametric `struct` — not just a specific option name — while standard
+  containers (`AbstractArray`, `Tuple`, `NamedTuple`, `AbstractDict`) are
+  excluded and keep displaying their full contents. **No breaking change**:
+  purely a display improvement; no API, type, or constructor changes. No
+  migration required.
+
 ## Non-breaking note (0.28.5-beta)
 
 - **`Data`: new `PseudoHamiltonianVectorField` / `AbstractPseudoHamiltonianVectorField`

CHANGELOG.md

@@ -6,6 +6,50 @@ All notable changes to CTBase will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.28.6-beta] - 2026-07-26
+
+### 🐛 Bug Fixes
+
+#### **Strategies** — display of parametric struct option values
+
+- **`_display_value`** (`Strategies/display_formatting.jl`) now shortens
+  **any** option value whose type is a parametric `struct` to just its
+  type name, instead of special-casing the `:alg` option name. Previously,
+  an option like `alg = Vern6()` (an `OrdinaryDiffEq` algorithm) displayed
+  its entire type-parameterized `repr` (e.g.
+  `Vern6{typeof(trivial_limiter!), typeof(trivial_limiter!),
+  FastBroadcast.Serial, Val{true}}(...)`) in the `show` tree output,
+  instead of just `Vern6`.
+- The new rule is based on the value's type (`isstructtype(T) &&
+  !isempty(T.parameters)`), not on the option's key name — `CTBase` has no
+  built-in knowledge of `:alg` or any downstream package's option-naming
+  convention. Standard containers (`AbstractArray`, `Tuple`, `NamedTuple`,
+  `AbstractDict`) are excluded and keep displaying their full contents,
+  since they are themselves parametric structs but their contents (not
+  their type name) are the useful display.
+- Fixes a latent bug in the previous key-based approach: an `:alg` option
+  holding a simple `Symbol`/`String` value would have displayed the type
+  name (`"Symbol"`) instead of the actual value.
+
+### 🧪 Testing
+
+- Added `_display_value` unit tests in `test_abstract_strategy.jl`
+  covering: simple values (`Int`, `Float64`, `Symbol`, `String`, `Bool`,
+  `Nothing`) unaffected, a parametric struct shortened to its type name,
+  and standard containers (`Vector`, `Tuple`, `NamedTuple`, `Dict`)
+  displayed in full.
+- Added integration tests in `test_abstract_strategy.jl` and
+  `test_strategy_options.jl` verifying that `show` (both the verbose
+  `MIME"text/plain"` form and the compact form) shortens a
+  `FakeParametricAlgorithm{A,B}` option value to its type name without
+  leaking field values or type parameters.
+- Full suite green: **4907/4907**
+
+### ✅ Compatibility
+
+- **No breaking changes**: purely a display fix; no API, type, or
+  constructor changes. See [BREAKING.md](BREAKING.md).
+
 ## [0.28.5-beta] - 2026-07-24
 
 ### ✨ New Features

Project.toml

@@ -1,6 +1,6 @@
 name = "CTBase"
 uuid = "54762871-cc72-4466-b8e8-f6c8b58076cd"
-version = "0.28.5-beta"
+version = "0.28.6-beta"
 authors = ["Olivier Cots <olivier.cots@irit.fr>", "Jean-Baptiste Caillau <caillau@univ-cotedazur.fr>"]
 
 [deps]

src/Strategies/contract/abstract_strategy.jl

@@ -512,7 +512,7 @@ function Base.show(io::IO, ::MIME"text/plain", strategy::T) where {T<:AbstractSt
             fmt.reset,
             " = ",
             fmt.value,
-            Options.value(opt),
+            _display_value(Options.value(opt)),
             fmt.reset,
             "  [",
             fmt.label,
@@ -568,7 +568,7 @@ function Base.show(io::IO, strategy::T) where {T<:AbstractStrategy}
                 fmt.reset *
                 "=" *
                 fmt.value *
-                "$(Options.value(v))" *
+                _display_value(Options.value(v)) *
                 fmt.reset for (k, v) in pairs(opts.options)
             ),
             ", ",

src/Strategies/contract/strategy_options.jl

@@ -722,7 +722,7 @@ function Base.show(io::IO, ::MIME"text/plain", opts::StrategyOptions)
             fmt.reset,
             " = ",
             fmt.value,
-            Options.value(opt),
+            _display_value(Options.value(opt)),
             fmt.reset,
             "  [",
             fmt.label,
@@ -762,7 +762,7 @@ function Base.show(io::IO, opts::StrategyOptions)
                 fmt.reset *
                 "=" *
                 fmt.value *
-                "$(Options.value(v))" *
+                _display_value(Options.value(v)) *
                 fmt.reset for (k, v) in pairs(_raw_options(opts))
             ),
             ", ",

src/Strategies/display_formatting.jl

@@ -39,3 +39,31 @@ function _print_labeled_multiline(
         end
     end
 end
+
+"""
+$(TYPEDSIGNATURES)
+
+Format an option value for display, shortening verbose parametric struct instances.
+
+Values whose type is a parametric struct (e.g. an ODE algorithm such as
+`Tsit5{...}`) are displayed as just the type name (e.g. `"Tsit5"`) instead of the
+full `repr`, which would otherwise include type parameters and field values.
+Standard containers (`AbstractArray`, `Tuple`, `NamedTuple`, `AbstractDict`) are
+excluded from this shortening since their contents are the useful information to
+display.
+
+# Arguments
+- `value`: Option value
+
+# Returns
+- `String`: Display representation of the value
+"""
+function _display_value(value)
+    T = typeof(value)
+    if isstructtype(T) &&
+        !isempty(T.parameters) &&
+        !(value isa Union{AbstractArray,Tuple,NamedTuple,AbstractDict})
+        return string(nameof(T))
+    end
+    return string(value)
+end

test/suite/strategies/test_abstract_strategy.jl

@@ -69,6 +69,13 @@ function Strategies.description(::Type{<:FakeStrategyWithDescription})
     return "A strategy for testing description display.\nSee: https://example.com"
 end
 
+# Fake parametric struct simulating a verbose algorithm type (e.g. an ODE solver
+# algorithm from OrdinaryDiffEq), used to test `_display_value` shortening.
+struct FakeParametricAlgorithm{A,B}
+    a::A
+    b::B
+end
+
 # ============================================================================
 # Test function
 # ============================================================================
@@ -284,6 +291,32 @@ function test_abstract_strategy()
             end
         end
 
+        Test.@testset "_display_value helper" begin
+            Test.@testset "simple values are unaffected" begin
+                Test.@test Strategies._display_value(200) == "200"
+                Test.@test Strategies._display_value(1.0e-8) == "1.0e-8"
+                Test.@test Strategies._display_value(:sparse) == "sparse"
+                Test.@test Strategies._display_value("hello") == "hello"
+                Test.@test Strategies._display_value(true) == "true"
+                Test.@test Strategies._display_value(nothing) == "nothing"
+            end
+
+            Test.@testset "parametric struct is shortened to type name" begin
+                value = FakeParametricAlgorithm(1, "x")
+                Test.@test Strategies._display_value(value) == "FakeParametricAlgorithm"
+                # The shortened form must not leak field values or type parameters
+                Test.@test !occursin("\"x\"", Strategies._display_value(value))
+                Test.@test !occursin("{", Strategies._display_value(value))
+            end
+
+            Test.@testset "standard containers are displayed in full" begin
+                Test.@test Strategies._display_value([1, 2, 3]) == string([1, 2, 3])
+                Test.@test Strategies._display_value((1, 2)) == string((1, 2))
+                Test.@test Strategies._display_value((; a=1)) == string((; a=1))
+                Test.@test Strategies._display_value(Dict(:a => 1)) == string(Dict(:a => 1))
+            end
+        end
+
         # ========================================================================
         # INTEGRATION TESTS
         # ========================================================================
@@ -333,6 +366,27 @@ function test_abstract_strategy()
                     Test.@test_nowarn show(stdout, Strategies.options(strategy))
                 end
             end
+
+            Test.@testset "Strategy display shortens parametric struct option values" begin
+                opts = Strategies.StrategyOptions(;
+                    alg=Options.OptionValue(FakeParametricAlgorithm(1, "x"), :user)
+                )
+                strategy = FakeStrategy(opts)
+
+                io = IOBuffer()
+                show(io, MIME("text/plain"), strategy)
+                verbose_output = String(take!(io))
+                Test.@test occursin("FakeParametricAlgorithm", verbose_output)
+                Test.@test !occursin("\"x\"", verbose_output)
+                Test.@test !occursin("{", verbose_output)
+
+                io = IOBuffer()
+                show(io, strategy)
+                compact_output = String(take!(io))
+                Test.@test occursin("FakeParametricAlgorithm", compact_output)
+                Test.@test !occursin("\"x\"", compact_output)
+                Test.@test !occursin("{", compact_output)
+            end
         end
     end
 end

test/suite/strategies/test_strategy_options.jl

@@ -8,6 +8,13 @@ import CTBase.Options
 const VERBOSE = isdefined(Main, :TestData) ? Main.TestData.VERBOSE : true
 const SHOWTIMING = isdefined(Main, :TestData) ? Main.TestData.SHOWTIMING : true
 
+# Fake parametric struct simulating a verbose algorithm type (e.g. an ODE solver
+# algorithm from OrdinaryDiffEq), used to test that display shortens such values.
+struct FakeParametricAlgorithm{A,B}
+    a::A
+    b::B
+end
+
 # ============================================================================
 # Test function
 # ============================================================================
@@ -258,6 +265,26 @@ function test_strategy_options()
                 Test.@test occursin("computed", output)
             end
 
+            Test.@testset "Display shortens parametric struct option values" begin
+                opts = Strategies.StrategyOptions(;
+                    alg=Options.OptionValue(FakeParametricAlgorithm(1, "x"), :user)
+                )
+
+                io = IOBuffer()
+                show(io, MIME"text/plain"(), opts)
+                verbose_output = String(take!(io))
+                Test.@test occursin("FakeParametricAlgorithm", verbose_output)
+                Test.@test !occursin("\"x\"", verbose_output)
+                Test.@test !occursin("{", verbose_output)
+
+                io = IOBuffer()
+                show(io, opts)
+                compact_output = String(take!(io))
+                Test.@test occursin("FakeParametricAlgorithm", compact_output)
+                Test.@test !occursin("\"x\"", compact_output)
+                Test.@test !occursin("{", compact_output)
+            end
+
             Test.@testset "Integration with OptionDefinition" begin
                 # Create OptionDefinition
                 opt_def = Options.OptionDefinition(