[SwayamInSync]

An error about a construct the verifier does not represent named only the function:

error: pick: unsupported statement: SwitchStmt

In a file with several functions, or a function with several switches, the user had to find the construct themselves. The converter recorded its 189 error sites as plain strings (std::vector<std::string> Errors), so no location was available to print.

The change gives every conversion error a source range and prints it as a compiler error is:

pick.cpp:4:3: error: pick: unsupported statement: SwitchStmt
    4 |   switch (x) { case 1: return 1; default: return 0; }
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• ASTConverter keeps CurrentRange, the range of the innermost declaration, statement, or expression being converted. convertFunction, convertStmt, and convertExpr set it with llvm::SaveAndRestore, and error(Message) records it. Each site therefore points at what it is about without being edited one by one. Sites outside the conversion of a function name their place: a member function's or template's declaration, and for the checks made after every function is converted (recursion without a measure, mutual recursion, an inductive predicate reached through another spec), the function's declaration.
• expandInductivePredicates reports through a callback with a location, the predicate's cppverify::inductive marker, instead of appending strings to the converter's list. Transform/ takes no dependency on the converter.
• The verifier prints a conversion error with Clang's TextDiagnostic, into its own stream rather than through the DiagnosticsEngine. Verification at compile time runs on another thread, and the engine is not thread-safe. It uses presumed locations, as Clang's driver does, so #line is honored. The JSON record carries the start and end of the range.

The message text is unchanged; saying in C++ terms what is unsupported is the second half of E2.

Docs: the tooling page shows the error with its line and caret, as a checked rejects example, and says where whole-function errors point. ARCHITECTURE describes the mechanism, and the release notes get an entry under "Running cpp-verify".

Testing: Verify/located_errors.cpp checks, with --strict-whitespace, the location, line, and caret of five errors: a statement (switch), a member function, a misplaced [[cppverify::trusted]], a non-bool inductive predicate, and a recursion without a measure, which is reported after conversion. It also checks the JSON record of the first. Both RUN lines fail on main. Three mutations fail it: no range for statements, no location for the checks made after conversion, and the old one-line printing.

Over all 396 Verify sources, converted with --lower-only, no converter error prints without a location now. Four other errors still do. Three are valid marker errors from UBChecks (valid marker must be a positive top-level conjunction clause, and two like it), and one is the reads check's error for a callee without a reads clause. Locating them changes UBChecks, which #40 changes too, so they follow once it merges.

Checked: the Verify suite passes in a release build and in a build with assertions (424 with the new test, 1 unsupported), as do the documentation examples and the site build with -W. A verdict differential against main over 431 Verify sources (the ULEB128 exhaustive decoder left out, as it has no error path) changes no verdict and no time; the new test's errors are errors on main too, without their locations.