layout: true class: typo, typo-selection --- count: false class: nord-dark, middle, center # 🐛 CMake CPM Target Conflict 2: The Shadow Variable ## The Sequel to a Three-Hour Debugging Session 🎬 ### From 11 Recommendations to 3 Compilation Errors to 1 Root Cause @luk036 👨‍💻 · 2026 📅 --- ### 📋 Agenda 🗺️ .pull-left[ **Part 1: The Portfolio** 📦 - 28 Repos, One Sweep - The Audit Findings **Part 2: The 11 Recommendations** 📋 - Hygiene, Guards, Docs, CI - The 3 fmt Guard Idioms **Part 3: The Implementation** ⚙️ - The Mechanical Changes - The Guard "Fix" ] .pull-right[ **Part 4: The Compilation Errors** 💥 - CPM Recursion - fmt ALIAS Conflict - absl IMPORTED vs REAL **Part 5: Root Cause** 🕳️ - The Shadow Variable - Minimal Reproduction **Part 6: Fix & Lessons** ✅ - The CACHE-write Idiom - 28 Repos Green ] --- class: nord-light, middle, center ## 📦 Part 1: The Portfolio --- ### The Task: 28 C++ Repos at Once 🎯 .pull-left[ **What I was asked to do:** - Audit the whole portfolio 🌐 - Suggest improvements 💡 - Implement ALL recommendations ⚙️ - Verify everything builds 🏗️ **The twist:** Every repo is a **header-only library** using: - CMake + CPM.cmake - doctest + GitHub Actions - `find_package` first → CPM fallback ] .pull-right[ .mermaid[ <pre> graph TD subgraph Portfolio["28 C++ Repos"] P1["ckpttn-cpp"] --> P2["netlistx-cpp"] P2 --> P3["xnetwork-cpp"] P3 --> P4["py2cpp"] P1 --> P5["digraphx-cpp"] P5 --> P6["netoptim-cpp"] P6 --> P7["ellalgo-cpp"] P8["fractions-cpp"] --> P9["projgeom-cpp"] P9 --> P10["rat-trig-cpp"] end style Portfolio fill:#e8f5e9,stroke:#2e7d32,stroke-width:3px style P1 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style P6 fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style P8 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px </pre> ] ] --- ### The Audit: Everything Looked Healthy ✅ .font-sm[ | Check | Result | |-------|--------| | Git repos | 27/28 (helloworld-cpp was not) | | CMakeLists.txt | 28/28 | | GitHub Actions CI | 27/28 (helloworld-cpp missing) | | Test files | 28/28 (doctest) | | README.md | 25/28 (lmi-solver, rat-trig-simple, helloworld missing) | | Last commit | All within 48h 🔥 | | Working tree | All clean | ] **First impression:** A well-maintained, disciplined portfolio. 🎯 But a deeper look revealed **11 recommendations**... --- class: nord-light, middle, center ## 📋 Part 2: The 11 Recommendations --- ### Rec 1–2: Hygiene First 🧹 **Rec 1: 26 tracked `.bak` files** in `.github/workflows/` across 16 repos ``` standalone.bak · style.bak · test.bak · benchmark.bak ``` All committed to git — zero reason to keep them. Deleted via `git rm`. 🗑️ **Rec 2: Broken CI badges** 🏷️ `digraphx-fast` and `digraphx-cpp` READMEs pointed at **`luk036/digraph-cpp`** — a repo that doesn't exist! ```markdown ❌ https://github.com/luk036/digraph-cpp/workflows/Ubuntu/badge.svg ✅ https://github.com/luk036/digraphx-fast/workflows/Ubuntu/badge.svg ``` --- ### Rec 3: The fmt Guard — 3 Inconsistent Idioms ⚠️ Every repo does `find_package(fmt)` → CPM fallback. But the guard differs: .mermaid[ <pre> graph LR subgraph Idiom1["Idiom 1 — set(CPM_fmt_ADDED YES)"] A1["ecgen, lmi-solver, mywheel\npy2cpp, xnetwork, csd\nnetlistx, ellalgo"] end subgraph Idiom2["Idiom 2 — list(APPEND CPM_PACKAGES fmt)"] A2["corr-solver, multiplierless"] end subgraph Idiom3["Idiom 3 — No guard at all"] A3["ckpttn, ginger, netoptim\nprojgeom, sphere-n, digraphx\nphysdes"] end Idiom1 --> Q{"Which one\nis correct?"} Idiom2 --> Q Idiom3 --> Q Q --> R["❓ Ask CPM's source code..."] style Idiom1 fill:#fff3e0,stroke:#e65100,stroke-width:3px style Idiom2 fill:#fff3e0,stroke:#e65100,stroke-width:3px style Idiom3 fill:#fff3e0,stroke:#e65100,stroke-width:3px style Q fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style R fill:#e3f2fd,stroke:#1565c0,stroke-width:3px </pre> ] --- ### Rec 3: What CPM Actually Checks 🔍 The reference presentation taught us: **read the source, don't guess.** .font-sm[ ```cmake # CPM 0.32.0 — cpm_check_if_package_already_added function(cpm_check_if_package_already_added CPM_ARGS_NAME CPM_ARGS_VERSION) if("${CPM_ARGS_NAME}" IN_LIST CPM_PACKAGES) # ← THIS is the check ... return() endif() endfunction() ``` ] **Key insight:** `set(CPM_fmt_ADDED YES)` is a **no-op** — CPM never reads it! So the plan was: **migrate everything to the `CPM_PACKAGES` idiom** and add it to the 7 unguarded repos. --- ### Rec 4–6: spdlog, Dead Code, Tests 🧩 **Rec 4: `SPDLOG_FMT_EXTERNAL` inconsistency** - ecgen/csd/netlistx: **missing** entirely - ckpttn: `ON` vs others: `YES` - physdes: bare `SPDLOG_FMT_EXTERNAL` (no value!) **Rec 5: Commented-out dead code** 🧟 Boost/cppcoro/GSL/xtensor blocks in 8 repos' `specific.cmake` **Rec 6: Test file naming** 📁 11 different conventions found → standardized to `test_*.cpp` --- ### Rec 7–9: Docs, Outliers, CI 📚 **Rec 7: Missing READMEs** - `lmi-solver-cpp`: only CI-enabled repo with no docs - `rat-trig-simple`: empty README (0 bytes) **Rec 8: `helloworld-cpp` outlier** 👽 No git, no CMake, no CI, no README → git-init + CMake + README + CI added **Rec 9: Missing CI workflows** - `netoptim-fast`: no `documentation.yaml` - `lmi-solver-cpp`: no install/docs workflows --- ### Rec 10–11: Variants & Version Pins 🔗 **Rec 10: `-simple` / `-fast` variants** 🧬 6 variants on lighter CI sets → documented the difference in READMEs **Rec 11: Cross-repo version pins** 🔐 24 pins verified — all tags exist, all consistent: .mermaid[ <pre> graph LR subgraph Producers["Producer Repos"] A["py2cpp\nv1.6.3"] B["ellalgo-cpp\nv1.6.8"] C["fractions-cpp\nv1.1.3"] end subgraph Consumers["Consumer Repos"] D["xnetwork, ecgen, mywheel..."] E["corr-solver, lmi-solver..."] F["projgeom, rat-trig"] end A --> D B --> E C --> F style Producers fill:#e8f5e9,stroke:#2e7d32,stroke-width:3px style Consumers fill:#e3f2fd,stroke:#1565c0,stroke-width:3px style A fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style B fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style C fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px </pre> ] --- class: nord-light, middle, center ## ⚙️ Part 3: The Implementation --- ### The Mechanical Sweep ⚡ All changes applied — nothing committed yet: .font-sm[ | Change | Scope | |--------|-------| | Delete `.bak` files | 26 files / 16 repos | | Fix badges | 2 repos | | Standardize fmt guard | 16 specific.cmake | | Standardize spdlog flag | 6 repos | | Remove dead code | 8 repos | | Rename test file | 1 repo | | Add READMEs | 2 repos | | git-init + CMake helloworld | 1 repo | | Add CI workflows | 3 repos | | Document variants | 10 READMEs | ] **Total: all 28 repos touched.** 🎉 --- ### The Guard "Fix" — My Mistake 🔥 I applied the `CPM_PACKAGES` guard everywhere: .font-sm[ ```cmake find_package(fmt CONFIG QUIET) if(fmt_FOUND) message(STATUS "Found system fmt: ${fmt_DIR}") if(NOT fmt IN_LIST CPM_PACKAGES) list(APPEND CPM_PACKAGES fmt) # ← My "fix" endif() else() CPMAddPackage(NAME fmt ...) endif() ``` ] **It compiled everywhere... in theory.** 🤔 The reference doc warned: *"CPM_PACKAGES from parent scope might not propagate to FetchContent's subdirectory scope"* 🔴 **I treated that as a hint. It was a trap.** --- class: nord-light, middle, center ## 💥 Part 4: The Compilation Errors --- ### Error 1: CPM Recursion — ckpttn-cpp 💀 ``` CMake Error at CPM_0.32.0.cmake:784 (string): Maximum recursion depth of 1000 exceeded Call Stack: CPM_0.32.0.cmake:390 (cpm_get_version_from_git_tag) FindPy2Cpp.cmake:2 (CPMAddPackage) CPM_0.32.0.cmake:204 (find_package) CPM_0.32.0.cmake:490 (cpm_find_package) FindPy2Cpp.cmake:2 (CPMAddPackage) # ← loop! ``` .mermaid[ <pre> graph LR A["CPMAddPackage\n(Py2Cpp)"] --> B{"Py2Cpp IN_LIST\nCPM_PACKAGES?"} B -- "No ❌" --> C["cpm_find_package"] C --> D["find_package(Py2Cpp)"] D --> E["FindPy2Cpp.cmake\n(generated module)"] E --> A style A fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style B fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style C fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style D fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style E fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px </pre> ] --- ### Error 2: fmt ALIAS Conflict — netoptim-fast 💥 **The EXACT error from the reference presentation:** ``` CMake Error at fmt/CMakeLists.txt:309 (add_library): add_library cannot create ALIAS target "fmt::fmt" because another target with the same name already exists. ``` .mermaid[ <pre> graph LR A["netoptim-fast specific.cmake\nfind_package(fmt) → system"] --> B["fmt::fmt = IMPORTED ✅"] C["fetched DiGraphXFast\nCPMAddPackage(fmt) unguarded"] --> D["CPM fetches fmt\ncreates fmt::fmt ALIAS"] B --> E["CONFLICT 💥"] D --> E style A fill:#e3f2fd,stroke:#1565c0,stroke-width:3px style B fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style C fill:#fff3e0,stroke:#e65100,stroke-width:3px style D fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style E fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px </pre> ] **Was this MY bug?** 🤔 My changes to netoptim-fast were only README + workflows... --- ### Error 3: absl IMPORTED vs REAL — netoptim-cpp 💢 ``` CMake Error at .../absl/abslTargets.cmake:42 (message): Some (but not all) targets in this export set were already defined. ``` .mermaid[ <pre> graph TD A["netoptim-cpp specific.cmake"] --> B["CPMAddPackage(DiGraphX)"] B --> C["DiGraphX CPM-adds abseil-cpp\n→ REAL absl::* targets"] A --> D["find_package(absl)\nconda system absl"] D --> E["→ IMPORTED absl::* targets"] C --> F["CONFLICT 💥\nREAL vs IMPORTED"] E --> F style A fill:#e3f2fd,stroke:#1565c0,stroke-width:3px style B fill:#fff3e0,stroke:#e65100,stroke-width:3px style C fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style D fill:#fff3e0,stroke:#e65100,stroke-width:3px style E fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style F fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px </pre> ] --- ### Which Errors Are MINE? 🕵️ The reference doc's lesson: *"Each project has a different dependency chain — one pattern doesn't fit all."* I ran a **stash test**: revert my changes → reconfigure → observe. .font-sm[ | Repo | Error | Mine? | |------|-------|-------| | ckpttn-cpp | CPM recursion | ✅ **Mine** (list(APPEND)) | | xnetwork-cpp | CPM recursion | ✅ **Mine** | | netoptim-cpp | CPM recursion | ✅ **Mine** | | netoptim-fast | fmt ALIAS conflict | ❌ Pre-existing (committed code) | | netoptim-cpp | absl IMPORTED vs REAL | ❌ Pre-existing | | netlistx-cpp | LNK2038 | ❌ Stale Debug/Release cache artifact | ] **Important:** Only fix MY regressions first — but the user asked for ALL local errors fixed. So both classes had to be solved. 🎯 --- class: nord-light, middle, center ## 🕳️ Part 5: Root Cause — The Shadow Variable --- ### CPM_PACKAGES is a CACHE INTERNAL Variable 📦 .font-sm[ ```cmake # CPM 0.32.0 — at the top of the file set(CPM_PACKAGES "" CACHE INTERNAL "" # ← CACHE INTERNAL ) # CPMRegisterPackage — after adding a package function(CPMRegisterPackage PACKAGE VERSION) list(APPEND CPM_PACKAGES ${PACKAGE}) set(CPM_PACKAGES ${CPM_PACKAGES} CACHE INTERNAL "") # ← updates the cache endfunction() ``` ] **`CACHE INTERNAL` = visible everywhere, in every scope.** 🌍 So why didn't my `list(APPEND ...)` work? --- ### list(APPEND) Creates a Shadow 🪤 **The bug is subtle:** .font-sm[ ```cmake # My code in specific.cmake (top-level scope) if(NOT fmt IN_LIST CPM_PACKAGES) list(APPEND CPM_PACKAGES fmt) # ← reads cache "", creates NORMAL var endif() ``` ] `list(APPEND)` on a cache variable: 1. Reads the cache value → `""` 2. Creates a **NORMAL variable** `CPM_PACKAGES = [fmt]` in the current directory scope 3. The normal variable **shadows** the cache — in this scope AND all child scopes .mermaid[ <pre> graph TD A["list(APPEND CPM_PACKAGES fmt)"] --> B["Reads CACHE = empty"] B --> C["Creates NORMAL var\nCPM_PACKAGES = [fmt]"] C --> D["NORMAL var shadows CACHE\nin current + child scopes"] style A fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style B fill:#e3f2fd,stroke:#1565c0,stroke-width:3px style C fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style D fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px </pre> ] --- ### Why FetchContent Breaks It 🧵 `CPMAddPackage` fetches deps via **FetchContent → add_subdirectory** — a CHILD scope. The child scope inherits the **normal-variable shadow** `[fmt]`, NOT the cache `[fmt;Py2Cpp]`: .mermaid[ <pre> graph TD subgraph Parent["Parent Scope (specific.cmake)"] N1["NORMAL var: [fmt]\n(shadow, from my list(APPEND))"] end subgraph Cache["CACHE INTERNAL (global)"] C1["[fmt;Py2Cpp]\n(CPM registered Py2Cpp here)"] end subgraph Child["FetchContent subdirectory\n(fetched dep's specific.cmake)"] Q{"Py2Cpp IN_LIST\nCPM_PACKAGES?"} end N1 -->|"inherited ↓"| Q C1 -.->|"shadowed ✗"| Q Q -->|"No → recursion 💥"| R["find_package(Py2Cpp)\n→ FindPy2Cpp.cmake\n→ CPMAddPackage\n→ infinite loop"] style N1 fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style C1 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style Q fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style R fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px </pre> ] --- ### Minimal Reproduction — Proven in 60 Seconds ⏱️ I wrote a tiny CMake test to **prove** the mechanism before touching 16 files: .font-sm[ ```cmake # CMakeLists.txt (parent) set(CPM_PACKAGES "" CACHE INTERNAL "") if(NOT fmt IN_LIST CPM_PACKAGES) list(APPEND CPM_PACKAGES fmt) # ← the shadow endif() function(CPMRegisterPackage PACKAGE VERSION) list(APPEND CPM_PACKAGES ${PACKAGE}) set(CPM_PACKAGES ${CPM_PACKAGES} CACHE INTERNAL "") endfunction() CPMRegisterPackage(Py2Cpp v1.6.3) add_subdirectory(sub) # ← child scope ``` ] .font-sm[ ```cmake # sub/CMakeLists.txt (child = FetchContent scope) if(Py2Cpp IN_LIST CPM_PACKAGES) message(STATUS "Py2Cpp FOUND — GOOD") else() message(STATUS "Py2Cpp NOT in list — RECURSION RISK") endif() ``` ] --- ### The Shadow Test Verdict 🧪 **`list(APPEND)` result — RECURSION CONFIRMED:** .font-sm[ ```text -- PARENT scope CPM_PACKAGES = [fmt] -- PARENT after register = [fmt] cache=[fmt;Py2Cpp] -- SUB scope CPM_PACKAGES = [fmt] -- SUB: Py2Cpp NOT in list -> RECURSION RISK ❌ ``` ] **`set(... CACHE ... FORCE)` result — CORRECT:** .font-sm[ ```text -- PARENT scope CPM_PACKAGES = [;fmt] -- PARENT after register = [fmt;Py2Cpp] -- SUB scope CPM_PACKAGES = [fmt;Py2Cpp] -- SUB: Py2Cpp FOUND in list - GOOD ✅ ``` ] **Root cause proven:** `list(APPEND)` on a `CACHE INTERNAL` var = normal-var shadow = broken across FetchContent scopes. 🎯 --- class: nord-light, middle, center ## ✅ Part 6: The Fix --- ### The Correct Idiom: Write the CACHE Directly 💪 .font-sm[ ```cmake # ❌ BROKEN: creates a normal-variable shadow if(NOT fmt IN_LIST CPM_PACKAGES) list(APPEND CPM_PACKAGES fmt) endif() # ✅ CORRECT: writes the CACHE INTERNAL variable directly if(NOT fmt IN_LIST CPM_PACKAGES) set(CPM_PACKAGES "${CPM_PACKAGES};fmt" CACHE INTERNAL "" FORCE) endif() ``` ] **`FORCE`** overwrites any existing cache value. No normal variable is created — the value propagates into every FetchContent child scope. 🌍 Applied to **18 specific.cmake files** (16 with the guard + netoptim-fast + netoptim-cpp). --- ### netoptim-cpp absl Fix — Don't Mix! 🎭 Per the reference doc: *"you cannot mix `find_package` and `CPMAddPackage` for the same dependency."* DiGraphX already CPM-adds abseil → check for the REAL target first: .font-sm[ ```cmake # If DiGraphX already added abseil via CPM, use its REAL targets if(TARGET absl::flat_hash_map) message(STATUS "Using CPM-provided abseil (from DiGraphX)") set(SPECIFIC_ABSEIL_LIBS absl::flat_hash_map) else() find_package(absl CONFIG QUIET) # ← only when NOT already provided ... endif() ``` ] **No more IMPORTED vs REAL collision.** 🧹 --- ### Verification: All 28 Repos Build 🏁 Fresh configure + build for EVERY repo (no stale caches): .font-sm[ | Repo | Before | After | |------|:------:|:-----:| | ckpttn-cpp | ❌ recursion | ✅ build | | xnetwork-cpp | ❌ recursion | ✅ build | | netoptim-cpp | ❌ recursion + absl | ✅ build | | netoptim-fast | ❌ fmt ALIAS | ✅ build | | all 24 others | ✅ / untested | ✅ build | ] **28/28 repos configure AND compile from scratch.** 🎉 --- ### What I Could Have Done Faster ⏳ .pull-left[ **The real cost breakdown:** - 🔥 **1 wrong assumption** → the `list(APPEND)` idiom - 🕵️ **2 pre-existing bugs** I had to prove weren't mine - 🏗️ **28 fresh builds** × 2 (find errors + verify fix) - ⏱️ ~1 hour of pure machine time ] .pull-right[ **What would have saved it:** - 📖 Read the reference's Attempt 5 as a **constraint**, not a hint - 🧪 Write the minimal repro **before** editing 16 files - 🔍 Check `git status` first to isolate my changes from committed code ] > "It took 6 attempts because I treated all projects the same. They weren't the same." 🎯 --- class: nord-light, middle, center ## 🎯 Key Takeaways --- ### Lessons Learned 📝 1. **`list(APPEND)` on a CACHE variable is a shadow trap** 🪤 It creates a normal variable that hides the cache from child scopes. Use `set(... CACHE INTERNAL "" FORCE)` instead. 2. **FetchContent scoping is the real enemy** 🧵 `add_subdirectory` inherits normal vars, not your intent. 3. **Distinguish YOUR bugs from pre-existing ones** 🕵️ Stash → revert → reconfigure. Fix your regression first, then the rest. 4. **Reference docs list failed attempts for a reason** 📖 "Couldn't test due to scoping" was a RED FLAG, not a TODO. 5. **Prove the mechanism before mass edits** 🧪 A 60-second minimal reproduction beats 16 broken files. 6. **Verification on 28 repos is inherently slow** ⏱️ Budget for machine time, not just decision time. --- ### The One-Slide Summary 🔑 .mermaid[ <pre> graph TD A["I applied\nlist(APPEND CPM_PACKAGES fmt)"] --> B["Normal-var shadow\nhides cache in child scopes"] B --> C["Fetched dep checks CPM_PACKAGES\n→ Py2Cpp not found"] C --> D["find_package → FindPy2Cpp.cmake\n→ CPMAddPackage → recursion 💥"] D --> E["Fix: set(... CACHE INTERNAL '' FORCE)"] E --> F["Value propagates everywhere\n28 repos build ✅"] style A fill:#fff3e0,stroke:#e65100,stroke-width:3px style B fill:#fff3e0,stroke:#e65100,color:#2e3440,stroke-width:3px style C fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style D fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style E fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style F fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px </pre> ] **One wrong CMake idiom → 3 error classes → 28 repos to verify.** 🎬 --- ### When `list(APPEND)` Meets `CACHE INTERNAL` 🧪 .font-sm[ ```cmake # CACHE INTERNAL — global, but shadow-able set(MY_LIST "" CACHE INTERNAL "") list(APPEND MY_LIST a) # creates NORMAL var shadow = [a] set(MY_LIST "${MY_LIST};a" CACHE INTERNAL "" FORCE) # updates cache directly ``` ] | Operation | Parent reads | Child reads | Verdict | |-----------|:------------:|:-----------:|:-------:| | `list(APPEND MY_LIST a)` | `[a]` (shadow) | `[a]` (shadow) | ❌ cache hidden | | `set(... CACHE INTERNAL "" FORCE)` | `[;a]` (cache) | `[a;b]` (cache) | ✅ propagates | **Rule of thumb:** when in doubt, write the CACHE variable directly. 🔑 --- ### The Real Lesson 🧠 .mermaid[ <pre> graph TD subgraph Cost["Cost of Guessing 🔥"] G1["❌ 3 error classes"] --> G2["❌ 28 repos × 2 builds"] G2 --> G3["❌ 1 hour machine time"] end subgraph Better["Better Approach 💡"] B1["✅ Stop. Read CPM source."] --> B2["✅ Treat doc warnings as constraints"] B2 --> B3["✅ Minimal repro first"] B3 --> B4["✅ Isolate my bugs via git stash"] B4 --> B5["✅ Apply ONE correct idiom"] end Cost --> Better style Cost fill:#fce4ec,stroke:#ad1457,stroke-width:3px style Better fill:#e8f5e9,stroke:#2e7d32,stroke-width:3px style G1 fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style G2 fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style G3 fill:#ffcdd2,stroke:#c62828,color:#2e3440,stroke-width:3px style B1 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style B2 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style B3 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style B4 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px style B5 fill:#c8e6c9,stroke:#2e7d32,color:#2e3440,stroke-width:3px </pre> ] --- ### Why Did It Take So Long? ⏰ .pull-left[ **The honest breakdown:** - 🔥 My own mistake: 1 wrong idiom applied to 16 files - 🕵️ Proving pre-existing bugs weren't mine: stash tests + clean rebuilds - 🏗️ Verification cost: 28 repos × 2 fresh builds each - ⚠️ Two false leads: stale-cache link error, benign pthread probes ] .pull-right[ **The 80/20:** - 20% of the time → writing the fixes - 80% of the time → **proving which errors were mine** and **verifying the fix** across 28 repos > "The fixes themselves were the small part." 💡 ] --- count: false class: nord-dark, middle, center # 🙏 Thank You ## Questions? 🎤 ### **"Write the CACHE. Don't shadow it. Verify everything."** Slides: `luk036.github.io/proglang/cmake-conflict2-remark.html` --- count: false class: nord-dark, middle, center # 👋 That's All Folks! ## **28 Repos, 11 Recommendations, 3 Errors, 1 Root Cause** 🚀 ### `set(CPM_PACKAGES "…;fmt" CACHE INTERNAL "" FORCE)` ✅