Use FileCheck and trace a diagnostic

Time: About 150 minutes: 40 reading, 80 lab, 20 testing, 10 notes.
Prerequisites: Day 16: Write focused diagnostic tests

Toolchain: current-main build

Use build/bin/clang++ and build/bin/llvm-lit from your llvm-main checkout, not whichever clang++ is first on PATH. Reproduce upstream behavior on current main and record the commit SHA. Setup guide

Learn

Textual output assertions and the diagnostic definition chain.

Read Reading

R12 · FileCheck manual
Basic checks, labels and captures · 25 min
R1 · Learn LLVM 17, Second Edition
Chapter 8: TableGen introduction, skim · 15 min

Reading budgets cover selected sections, not whole chapters. Link to the book; this site does not reproduce it.

Build Build or investigate

Read an existing AST or CodeGen test using FileCheck.
Make a scratch check for one meaningful output property.
Trace yesterday’s diagnostic through a .td definition and a Sema call site.
Avoid checks against unstable addresses or SSA numbering.

Done when

One focused FileCheck test and a trace from diagnostic ID to source location.

Recall question

When is -verify a better fit than checking stderr with FileCheck?

Completion checks

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Notes

Saved only in this browser. Keep it short enough to finish in ten minutes; none of the prompts are required. All notes, export and import