Remove `rustc::existing_doc_keyword` lint.

`CheckAttrVisitor::check_doc_keyword` checks `#[doc(keyword = "..")]`
attributes to ensure they are on an empty module, and that the value is
a non-empty identifier.

The `rustc::existing_doc_keyword` lint checks these attributes to ensure
that the value is the name of a keyword.

It's silly to have two different checking mechanisms for these
attributes. This commit does the following.
- Changes `check_doc_keyword` to check that the value is the name of a
  keyword (avoiding the need for the identifier check, which removes a
  dependency on `rustc_lexer`).
- Removes the lint.
- Updates tests accordingly.

There is one hack: the `SelfTy` FIXME case used to used to be handled by
disabling the lint, but now is handled with a special case in
`is_doc_keyword`. That hack will go away if/when the FIXME is fixed.

Co-Authored-By: Guillaume Gomez <guillaume1.gomez@gmail.com>

4 files changed, 6 insertions, 5 deletions

diff --git a/tests/rustdoc-gui/search-result-color.goml b/tests/rustdoc-gui/search-result-color.goml
index e8da43eb896..e6dd504d703 100644
--- a/tests/rustdoc-gui/search-result-color.goml
+++ b/tests/rustdoc-gui/search-result-color.goml
@@ -140,7 +140,8 @@ define-function: (
     },
 )
 
-go-to: "file://" + |DOC_PATH| + "/test_docs/index.html?search=coo"
+// Searching for the `for` keyword
+go-to: "file://" + |DOC_PATH| + "/test_docs/index.html?search=fo"
 
 // This is needed so that the text color is computed.
 show-text: true
diff --git a/tests/rustdoc-gui/search-result-keyword.goml b/tests/rustdoc-gui/search-result-keyword.goml
index 370edce2ddd..02305f2587c 100644
--- a/tests/rustdoc-gui/search-result-keyword.goml
+++ b/tests/rustdoc-gui/search-result-keyword.goml
@@ -1,8 +1,8 @@
 // Checks that the "keyword" results have the expected text alongside them.
 go-to: "file://" + |DOC_PATH| + "/test_docs/index.html"
-write-into: (".search-input", "CookieMonster")
+write-into: (".search-input", "for")
 // To be SURE that the search will be run.
 press-key: 'Enter'
 // Waiting for the search results to appear...
 wait-for: "#search-tabs"
-assert-text: (".result-keyword .result-name", "keyword CookieMonster")
+assert-text: (".result-keyword .result-name", "keyword for")
diff --git a/tests/rustdoc-gui/search-tab.goml b/tests/rustdoc-gui/search-tab.goml
index 4329726398c..3879c127fd0 100644
--- a/tests/rustdoc-gui/search-tab.goml
+++ b/tests/rustdoc-gui/search-tab.goml
@@ -78,7 +78,7 @@ call-function: ("check-colors", {
 set-window-size: (851, 600)
 
 // Check the size and count in tabs
-assert-text: ("#search-tabs > button:nth-child(1) > .count", " (25) ")
+assert-text: ("#search-tabs > button:nth-child(1) > .count", " (26) ")
 assert-text: ("#search-tabs > button:nth-child(2) > .count", " (6)  ")
 assert-text: ("#search-tabs > button:nth-child(3) > .count", " (0)  ")
 store-property: ("#search-tabs > button:nth-child(1)", {"offsetWidth": buttonWidth})
diff --git a/tests/rustdoc-gui/src/test_docs/lib.rs b/tests/rustdoc-gui/src/test_docs/lib.rs
index 91aa2c3fae5..dae13d9ac18 100644
--- a/tests/rustdoc-gui/src/test_docs/lib.rs
+++ b/tests/rustdoc-gui/src/test_docs/lib.rs
@@ -156,7 +156,7 @@ pub enum AnEnum {
     WithVariants { and: usize, sub: usize, variants: usize },
 }
 
-#[doc(keyword = "CookieMonster")]
+#[doc(keyword = "for")]
 /// Some keyword.
 pub mod keyword {}