tree e95d893fd485c7cc236eb392df0495ee4027498e
parent d5012a7ed19c1e75e413373fa22c5f1b08a9ee29
author adonovan <adonovan@google.com> 1585069886 -0700
committer Copybara-Service <copybara-worker@google.com> 1585069980 -0700

bazel syntax: add FileOptions

FileOptions is a set of per-file options that control the front-end ("static")
processing of a single Starlark file: scanning, parsing, validation,
and, eventually, compilation.

FileOptions determine language dialect and "code generation",
like the options to a compiler. Different files may have different options,
as in the case of BUILD and .bzl files, for example.
By contrast, a StarlarkSemantics affects only dynamic behavior,
and is carried down the thread, possibly through many files that
vary in their FileOptions.

FileOptions are specified at the construction of a StarlarkFile (parsing)
and are retained by it thereafter. This reduces the burden of ensuring
that consistent options are provided to the operations of parsing and validation
when these steps are widely separated in the source, as is often the case
in Bazel.

This change allows Copybara do validation on all its files.
It was previously unable because it could not select validation
options "a la carte". This will soon allow us to assume that all
files are resolved before execution.

The API for creating a Starlark thread is getting more verbose.
This is temporary; to "refactor" a term in an equation one must
first expand it out.

Details:

- Add FileOptions parameters to scanner, parser, and their wrappers.
- Remove the StarlarkSemantics parameter from getUndeclaredNameError.
  It was only used for an assertion.
- Move StarlakSemantics into the evaluator package.
  ValidationTest no longer depends on semantics or lib.packages.
- Decompose the validator's previous isBuildFile parameter into
  separate features: top-level rebinding, whether to call setScope, etc.
- Simplify the "restrict string escapes" feature by pushing it
  from the validator to the scanner.
- Simplify the "load disregards privacy" feature by pushing it
  from the syntax tree into the validator. Delete parseVirtualBuildFile.
- Add a placeholder for a "load binds globally" feature,
  for load in the REPL and for upcoming changes to the implementation
  of the prelude. Its implementation will come later.
- Move the "load of private symbol" check from Eval to Validator.

This is a breaking API change for Copybara.

PiperOrigin-RevId: 302691302