string: Use 're.Pattern.search' instead of 're.Pattern.match'

[tinez]

Change Summary

Rust's Regex.is_match behaves like Python's re.Pattern.search, here's a snippet from the docs of the former:

Returns true if and only if there is a match for the regex anywhere in the haystack given.

Given the implementation of the regex matching mechanism for the validators.string.Pattern, this leads to an inconsistent behavior:

import re
from pydantic import BaseModel, Field

class A(BaseModel):
    b: str = Field(pattern=r"[a-z]")
    c: str = Field(pattern=re.compile(r"[a-z]"))

A.model_validate({"b": "Abc", "c": "Abc"})

In this snippet of code, b will validate fine, but c won't.

Since the test cases for string already establish the expected behavior (the Rust's Regex.is_match case), let's use re.Pattern.search instead of re.Pattern.match to unify the results when a re.Pattern object is passed.

Related issue number

fix #1367

Checklist

• Unit tests for the changes exist
• Documentation reflects the changes where applicable
• Pydantic tests pass with this pydantic-core (except for expected changes)
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!

[codspeed-hq]

CodSpeed Performance Report

Merging #1368 will not alter performance

_{Comparing tinez:unify-constained-string-pattern-behavior (d02dc18) with main (0e6b377)}

Summary

✅ 155 untouched benchmarks

[sydney-runkle]

Great, thanks!

[tinez]

Thanks for merging the MR and for maintaining this awesome lib!