In @exportS3method parse class name from function name

Fixes #1085

NEWS.md

@@ -1,5 +1,8 @@
 # roxygen2 (development version)
 
+* `@exportS3method pkg::generic` now works even when `pkg::generic` isn't 
+  imported by your package (#1085).
+
 * roxygen2 no longer generates invalid HTML (#1290).
 
 * All warning messages have been reviewed to hopefully be more informative

R/namespace.R

@@ -174,15 +174,39 @@ roxy_tag_ns.roxy_tag_exportS3Method <- function(x, block, env, import_only = FAL
   }
 
   obj <- block$object
-  if (length(x$val) < 2 && !inherits(obj, "s3method")) {
-    warn_roxy_tag(x, "must be used with an S3 method when it has 0 or 1 values")
-    return()
-  }
 
   if (identical(x$val, "")) {
+    if (!inherits(obj, "s3method")) {
+      warn_roxy_tag(x, "must be used with an known S3 method")
+      return()
+    }
+
     method <- attr(obj$value, "s3method")
   } else if (length(x$val) == 1) {
-    method <- c(x$val, attr(obj$value, "s3method")[[2]])
+    if (!inherits(obj, "function")) {
+      warn_roxy_tag(x, "must be used with a function")
+      return()
+    }
+
+    if (!str_detect(x$val, "::")) {
+      warn_roxy_tag(x, "must have form package::generic")
+      return()
+    }
+
+    generic <- str_split(x$val, "::")[[1]]
+    generic_re <- paste0("^", generic[[2]], "\\.")
+
+    if (!str_detect(obj$alias, generic_re)) {
+      warn_roxy_tag(x, c(
+        "doesn't match function name",
+        x = "Expected to see {.str {generic[[2]]}} to match {.str {x$val}}",
+        i = "Function name is {.str {obj$alias}}"
+      ))
+      return()
+    }
+
+    class <- str_remove(obj$alias, generic_re)
+    method <- c(x$val, class)
   } else {
     method <- x$val
   }

tests/testthat/_snaps/namespace.md

@@ -1,6 +1,20 @@
-# @exportS3method generatedsS3method()
+# @exportS3method generates fully automatically
 
-    [<text>:1] @exportS3Method must be used with an S3 method when it has 0 or 1 values
+    [<text>:2] @exportS3Method must be used with an known S3 method
+
+# @exportS3method can extract class from generic
+
+    [<text>:2] @exportS3Method must have form package::generic
+
+---
+
+    [<text>:2] @exportS3Method must be used with a function
+
+---
+
+    [<text>:2] @exportS3Method doesn't match function name
+    x Expected to see "foo" to match "pkg::foo"
+    i Function name is "foo1.bar"
 
 # poorly formed importFrom throws error
 

tests/testthat/test-namespace.R

@@ -75,33 +75,53 @@ test_that("export handles non-syntactic names", {
   expect_equal(out, "S3method(\"foo-bar\",integer)")
 })
 
-test_that("@exportS3method generatedsS3method()", {
-  out <- roc_proc_text(namespace_roclet(),
-    "#' @exportS3Method
+test_that("@exportS3method generates fully automatically", {
+  out <- roc_proc_text(namespace_roclet(),"
+    #' @exportS3Method
     mean.foo <- function(x) 'foo'
   ")
   expect_equal(out, "S3method(mean,foo)")
 
-  out <- roc_proc_text(namespace_roclet(),
-    "#' @exportS3Method base::mean
-    mean.foo <- function(x) 'foo'
-  ")
-  expect_equal(out, "S3method(base::mean,foo)")
-
   expect_snapshot_warning(
-    roc_proc_text(namespace_roclet(),
-      "#' @exportS3Method base::mean
-      NULL
+    roc_proc_text(namespace_roclet(), "
+      #' @exportS3Method
+      f <- function(x) 'foo'
     ")
   )
+})
 
+test_that("@exportS3methd can create literal directive", {
   out <- roc_proc_text(namespace_roclet(),
     "#' @exportS3Method base::mean foo
     NULL
   ")
   expect_equal(out, "S3method(base::mean,foo)")
+})
 
-
+test_that("@exportS3method can extract class from generic", {
+  out <- roc_proc_text(namespace_roclet(), "
+    #' @exportS3Method pkg::foo
+    foo.bar <- function(x) 'foo'
+  ")
+  expect_equal(out, "S3method(pkg::foo,bar)")
+
+  block <- "
+    #' @exportS3Method pkg_foo
+    foo.bar <- function(x) 'foo'
+  "
+  expect_snapshot_warning(roc_proc_text(namespace_roclet(), block))
+
+  block <- "
+    #' @exportS3Method pkg::foo
+    foo1.bar <- 10
+  "
+  expect_snapshot_warning(roc_proc_text(namespace_roclet(), block))
+
+  block <- "
+    #' @exportS3Method pkg::foo
+    foo1.bar <- function(x) 'foo'
+  "
+  expect_snapshot_warning(roc_proc_text(namespace_roclet(), block))
 })
 
 test_that("exportClass overrides default class name", {