A problem when installing blueprint: automatical upgrading

Stream: mathlib4

[Nick_adfor]

I added blueprint to my project on v4.26.0-rc2, yet it has something to automatically upgrade to v4.27.0 but I do not want to upgrade since some files were conflict.

lakefile.lean contents:

import Lake
open Lake DSL

require mathlib from git
  "https://github.com/leanprover-community/mathlib4.git"
    @ "v4.26.0-rc2"

package "ThePolynomialMethod" where
lean_lib "ThePolynomialMethod" where

require checkdecls from git "https://github.com/PatrickMassot/checkdecls.git"

meta if get_config? env = some "dev" then
require «doc-gen4» from git
  "https://github.com/leanprover/doc-gen4" @ "main"

Error:

1. API duplicate declaration conflicts

   error: Batteries/Lean/EStateM.lean:43:16: `EStateM.run_pure` has already been declared
   error: Batteries/Lean/Except.lean:55:16: `ExceptT.run_mk` has already been declared
   error: Batteries/Lean/System/IO.lean:28:4: `IO.waitAny'` has already been declared
   error: Batteries/Control/OptionT.lean:27:16: `OptionT.run_monadMap` has already been declared

2. Type class instance synthesis failures

   error: Batteries/Data/ByteSlice.lean:55:11: failed to synthesize instance of type class Monad m
   error: Batteries/Lean/PersistentHashSet.lean:17:23: invalid `do` notation, expected type is not a monad application
   error: Aesop/Util/UnorderedArraySet.lean:98:21: failed to synthesize instance of type class ForIn m (Array α) α
   error: Batteries/Data/RBMap/Basic.lean:119:11: failed to synthesize instance of type class Monad m

3. File format incompatibility (invalid .olean headers)

   error: Batteries/CodeAction/Deprecated.lean:6:0: failed to read file '.../Lean/Elab/BuiltinTerm.olean', invalid header
   error: Qq/ForLean/ReduceEval.lean:1:0: failed to read file '.../Lean/Data.olean', invalid header
   error: Batteries/CodeAction/Attr.lean:6:0: failed to read file '.../Lean/Elab/Import.olean', invalid header
   error: Batteries/Tactic/Case.lean:6:0: failed to read file '.../Lean/Elab/Do.olean', invalid header

4. Type mismatches due to String API changes

   error: Batteries/Lean/Meta/UnusedNames.lean:55:44: Application type mismatch:
     The argument suffix has type String.Slice but is expected to have type Substring.Raw
   error: Mathlib/Tactic/Linter/Header.lean:131:21: Application type mismatch:
     The argument line.take "Authors: ".length has type String.Slice but is expected to have type String

5. Option structure field changes

   error: Aesop/Check.lean:20:6: `group` is not a field of structure `Option.Decl`
   error: LeanSearchClient/Basic.lean:9:4: `group` is not a field of structure `Lean.Option.Decl`

6. Numerous deprecation warnings
   From the output, we can see many warnings about deprecated String APIs, indicating a major refactor of the String module:

   • String.revFindAux → String.Pos.revFind?
   • String.trim → String.trimAscii
   • String.toSubstring → String.toRawSubstring
   • String.takeRight → String.takeEnd
   • String.trimLeft → String.trimAsciiStart