Sourced from cuelang.org/go's releases.

v0.17.0

Changes which may break some users are marked below with: ⚠️

Language

The active try experiment renames the new fallback keyword, used with for comprehensions, to otherwise. fallback continues to be accepted for now, but is rewritten to the new form.

The active aliasv2 experiment now allows ~(X) as an alternative to ~X for the single postfix alias form. ~X is also rewritten as ~(X) for the sake of consistency and clarity.

Language versions v0.17.0 and later allow omitting commas in multi-line lists. Just like a newline after a struct field implies a comma, a newline after a list element now implies a comma as well.

Language versions v0.17.0 and later allow a newline or a comma before the closing bracket of an index expression, matching how lists and func arguments allow omitting trailing commas.

The language spec is tweaked to make $ a valid identifier, which was already allowed by the parser and evaluator.

⚠️ Support for the infix div, mod, quo, and rem operators has been removed. Since late 2020, these infix forms have been undocumented and rewritten by cue fix to the new function calls.

The new shortcircuit experiment

This release introduces the shortcircuit experiment, which changes the && and || operators to not evaluate the right operand if the left operand alone determines the result.

This matches the behavior already documented in the CUE spec and is consistent with most mainstream languages, but for the sake of a smooth transition for end users, we are rolling out this change via an experiment.

You can try this experiment via the @experiment(shortcircuit) file attribute. To mimic the old behavior with the experiment, you can use a hidden field:

_y: Y
if X && _y {}

Evaluator

Comprehensions

The comprehension algorithm now waits to run a comprehension's body until the fields it reads have a concrete value, rather than trying to produce its fields up front. This resolves a number of long-standing bugs, most notably the last known regressions from evalv2, where a comprehension that should have resolved instead failed as an incomplete value or a cycle.

This design also greatly simplifies upcoming evaluator work, such as introducing new builtins to replace comparing values to bottom, as well as the design of evalv4.

Other changes

The evaluator no longer deduplicates errors just by position, which was causing some useful errors from disjunctions or standard library calls to be dropped incorrectly.

Several long-standing cycle-detection bugs have been fixed, such as self-referential uses of matchN and matchIf, self-feeding disjunctions, and comprehensions that read a let binding which refers back to the comprehension's own fields.

Fixed a bug where the same package imported via different qualified import paths (e.g. foo.com/bar@v0 or foo.com/bar:baz) did not share the same hidden field namespace.

Resolving an unversioned import from a dependency module now respects that module's own default major version, instead of always using the main module's default.

Fix a number of issues where cue def could produce invalid CUE output, such as due to name conflicts.

... (truncated)

• 0fc639b [release-branch.v0.17] internal/mod: resolve module replacements via minimum-...
• e73658d cue/format: revert #4296 regression test
• c3f08a1 cue/format: revert manual-AST field alignment fix
• 60e1bb7 cue/format: revert issue #1006 test cases
• 3f7aafe cue/format: revert list and call argument column alignment fix
• e2eb7f5 cue/format: revert spurious empty line fix
• 0fa6c09 cue/format: revert Option-behavior test
• 1e07f16 cue/format: revert default tab width change from 8 to 4
• 7190842 cue/format: revert multiline string interpolation indentation fix
• 8d2db9d internal/cueexperiment: teach v0.17 about the formatv2 experiment
• Additional commits viewable in compare view