[SR-15051] Swift should suggest updating existing @available attribute when you use an insufficiently available declaration

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Feature
Clarity
Clearly specified
Activity status
Stale
Tech stack
cpp, swift
Domain
compilers, testing-qa

Research direction

Start in TypeCheckAvailability.cpp at fixAvailabilityForDecl() and inspect the existing availability diagnostic tests. Trace the early return for declarations with an existing @available attribute, then cover simple, multiple-OS, and long-form attributes. Done means diagnostics suggest replacing the insufficient availability version and the relevant tests pass.

Written by the indexing model from the issue text.

Description

availability compiler diagnostics quality fix-its good first issue improvement type checker
Previous ID SR-15051
Radar rdar://problem/81802673
Original Reporter @beccadax
Type Improvement
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, DiagnosticsQoI, StarterBug
Assignee mininny (JIRA)
Priority Medium

md5: 9db411fbe711e822a955f04325204e6d

Issue Description:

Currently, fixAvailabilityForDecl() in TypeCheckAvailability.cpp exits early if there is already an @available attribute on the declaration, with a comment noting work that should be done in the future:

/// Emit a diagnostic note and Fix-It to add an @available attribute
/// on the given declaration for the given version range.
static void fixAvailabilityForDecl(SourceRange ReferenceRange, const Decl *D,
                                   const VersionRange &RequiredRange,
                                   ASTContext &Context) {
  // ...irrelevant code omitted...

  if (getActiveAvailableAttribute(D, Context)) {
    // For QoI, in future should emit a fixit to update the existing attribute.
    return;
  }

Indeed, we should make this change. For instance, if you give the compiler this code:

@available(macOS 42, *) func foo() {}

@available(macOS 12, *) func bar() {
    foo()
}

Swift should emit a note with a fix-it replacing "macOS 12" with "macOS 42".

Your implementation, should you choose to commit it, should test not only this easy case with one simple @available attribute, but also cases with multiple OSes and long-form @available attributes. You will certainly need to update some existing tests; those might adequately cover this, but I'm not sure.

Dominant language
Swift
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