Module rustc_borrowck::type_check

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This pass type-checks the MIR to ensure it is not broken.


  • canonical ๐Ÿ”’
  • input_output ๐Ÿ”’
    This module contains code to equate the input/output types appearing in the MIR with the expected input/output types from the function signature. This requires a bit of processing, as the expected types are supplied to us before normalization and may contain opaque impl Trait instances. In contrast, the input/output types found in the MIR (specifically, in the special local variables for the RETURN_PLACE the MIR arguments) are always fully normalized (and contain revealed impl Trait values).
  • liveness ๐Ÿ”’
  • relate_tys ๐Ÿ”’



  • BorrowCheckContext ๐Ÿ”’
  • Runs infcx.instantiate_opaque_types. Unlike other TypeOps, this is not canonicalized - it directly affects the main InferCtxt that we use during MIR borrowchecking.
  • A collection of region constraints that must be satisfied for the program to be considered well-typed.
  • MirTypeckResults ๐Ÿ”’
    Holder struct for passing results from MIR typeck to the rest of the non-lexical regions inference computation.
  • TypeChecker ๐Ÿ”’
    The MIR type checker. Visits the MIR and enforces all the constraints needed for it to be valid and well-typed. Along the way, it accrues region constraints โ€“ these can later be used by NLL region checking.
  • TypeVerifier ๐Ÿ”’
    Verifies that MIR types are sane to not crash further checks.


  • FieldAccessError ๐Ÿ”’
  • The Locations type summarizes where region constraints are required to hold. Normally, this is at a particular point which created the obligation, but for constraints that the user gave, we want the constraint to hold at all points.



  • mirbug ๐Ÿ”’
  • type_check ๐Ÿ”’
    Type checks the given mir in the context of the inference context infcx. Returns any region constraints that have yet to be proven. This result includes liveness constraints that ensure that regions appearing in the types of all local variables are live at all points where that local variable may later be used.