'UseMethod' used in an inappropriate fashion

[wlandau]

I am having problems with S3 and development covr (89029d4). CRAN covr appears unaffected.

# Example file with S3:
source <- quote({
  mtd <- function(x, ...) {
    UseMethod("mtd")
  }

  mtd.cls <- function(x, ...) {
    x[[1]]
  }
})

# A test:
test <- quote({
  library(testthat)
  test_that("", {
    x <- structure(list("x"), class = "cls")
    expect_equal(mtd(x), "x")
  })
})

# The test passes.
eval(source)
eval(test)

# The same test fails with https://github.com/r-lib/covr/commit/89029d4670c09a106bbadfb384eec8b7ed42e885.
# Passes with CRAN covr.
writeLines(deparse(source), "source.R")
writeLines(deparse(test), "test.R")
library(covr)
file_coverage("source.R", "test.R")
#> Error: Test failed: ''
#> * 'UseMethod' used in an inappropriate fashion
#> 1: expect_equal(mtd(x), "x") at test.R:5
#> 2: quasi_label(enquo(object), label, arg = "object")
#> 3: eval_bare(get_expr(quo), get_env(quo))
#> 4: mtd(x)
#> 5: identity({
#>        covr:::count("source.R:3:9:3:24:9:24:3:3")
#>        UseMethod("mtd")
#>    }) at source.R:3

^{Created on 2019-08-08 by the reprex package (v0.3.0)}

[wlandau]

Thanks @jimhester!