diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index b81f7a24270..09a3e53c7f0 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -41,9 +41,6 @@ use std::convert::TryFrom;
 use std::fmt;
 use std::mem;
 
-#[cfg(test)]
-mod tests;
-
 /// A "Label" is an identifier of some point in sources,
 /// e.g. in the following code:
 ///
diff --git a/compiler/rustc_ast/src/ast/tests.rs b/compiler/rustc_ast/src/ast/tests.rs
deleted file mode 100644
index 8ba55bf037b..00000000000
--- a/compiler/rustc_ast/src/ast/tests.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-use super::*;
-
-// Are ASTs encodable?
-#[test]
-fn check_asts_encodable() {
-    fn assert_encodable<
-        T: for<'a> rustc_serialize::Encodable<rustc_serialize::json::Encoder<'a>>,
-    >() {
-    }
-    assert_encodable::<Crate>();
-}
diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index 0434997977a..179a184536e 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -343,10 +343,7 @@ fn run_compiler(
                 return early_exit();
             }
 
-            if sess.opts.debugging_opts.parse_only
-                || sess.opts.debugging_opts.show_span.is_some()
-                || sess.opts.debugging_opts.ast_json_noexpand
-            {
+            if sess.opts.debugging_opts.parse_only || sess.opts.debugging_opts.show_span.is_some() {
                 return early_exit();
             }
 
@@ -375,7 +372,7 @@ fn run_compiler(
 
             queries.global_ctxt()?;
 
-            if sess.opts.debugging_opts.no_analysis || sess.opts.debugging_opts.ast_json {
+            if sess.opts.debugging_opts.no_analysis {
                 return early_exit();
             }
 
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index e6c9c6693c5..3c867e308c4 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -27,7 +27,6 @@ use rustc_passes::{self, hir_stats, layout_test};
 use rustc_plugin_impl as plugin;
 use rustc_query_impl::{OnDiskCache, Queries as TcxQueries};
 use rustc_resolve::{Resolver, ResolverArenas};
-use rustc_serialize::json;
 use rustc_session::config::{CrateType, Input, OutputFilenames, OutputType};
 use rustc_session::cstore::{MetadataLoader, MetadataLoaderDyn};
 use rustc_session::output::{filename_for_input, filename_for_metadata};
@@ -59,10 +58,6 @@ pub fn parse<'a>(sess: &'a Session, input: &Input) -> PResult<'a, ast::Crate> {
         }
     })?;
 
-    if sess.opts.debugging_opts.ast_json_noexpand {
-        println!("{}", json::as_json(&krate));
-    }
-
     if sess.opts.debugging_opts.input_stats {
         eprintln!("Lines of code:             {}", sess.source_map().count_lines());
         eprintln!("Pre-expansion node count:  {}", count_nodes(&krate));
@@ -423,10 +418,6 @@ pub fn configure_and_expand(
         hir_stats::print_ast_stats(&krate, "POST EXPANSION AST STATS");
     }
 
-    if sess.opts.debugging_opts.ast_json {
-        println!("{}", json::as_json(&krate));
-    }
-
     resolver.resolve_crate(&krate);
 
     // Needs to go *after* expansion to be able to check the results of macro expansion.
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 1327bf6fcd4..a178cca6d10 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -644,8 +644,6 @@ fn test_debugging_options_tracking_hash() {
     // Make sure that changing an [UNTRACKED] option leaves the hash unchanged.
     // This list is in alphabetical order.
     untracked!(assert_incr_state, Some(String::from("loaded")));
-    untracked!(ast_json, true);
-    untracked!(ast_json_noexpand, true);
     untracked!(borrowck, String::from("other"));
     untracked!(deduplicate_diagnostics, false);
     untracked!(dep_tasks, true);
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 66198dff2ae..ae32fd2dee9 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1207,10 +1207,6 @@ options! {
     assert_incr_state: Option<String> = (None, parse_opt_string, [UNTRACKED],
         "assert that the incremental cache is in given state: \
          either `loaded` or `not-loaded`."),
-    ast_json: bool = (false, parse_bool, [UNTRACKED],
-        "print the AST as JSON and halt (default: no)"),
-    ast_json_noexpand: bool = (false, parse_bool, [UNTRACKED],
-        "print the pre-expansion AST as JSON and halt (default: no)"),
     binary_dep_depinfo: bool = (false, parse_bool, [TRACKED],
         "include artifacts (sysroot, crate dependencies) used during compilation in dep-info \
         (default: no)"),
diff --git a/src/test/ui/ast-json/ast-json-ice.rs b/src/test/ui/ast-json/ast-json-ice.rs
deleted file mode 100644
index ce93e4b5d4b..00000000000
--- a/src/test/ui/ast-json/ast-json-ice.rs
+++ /dev/null
@@ -1,56 +0,0 @@
-// Test that AST json serialization doesn't ICE (#63728).
-
-// revisions: expand noexpand
-
-//[expand] compile-flags: -Zast-json
-//[noexpand] compile-flags: -Zast-json-noexpand
-
-// check-pass
-// dont-check-compiler-stdout - don't check for any AST change.
-
-enum V {
-    A(i32),
-    B { f: [i64; 3 + 4] }
-}
-
-trait X {
-    type Output;
-    fn read(&self) -> Self::Output;
-    fn write(&mut self, _: Self::Output);
-}
-
-macro_rules! call_println {
-    ($y:ident) => { println!("{}", $y) }
-}
-
-fn main() {
-    let x: (i32) = 35;
-    let y = x as i64<> + 5;
-
-    call_println!(y);
-
-    struct A;
-}
-
-// Regressions tests for issues #78398 and #78510 (captured tokens in associated and foreign items)
-
-struct S;
-
-macro_rules! mac_extern {
-    ($i:item) => {
-        extern "C" { $i }
-    }
-}
-macro_rules! mac_assoc {
-    ($i:item) => {
-        impl S { $i }
-        trait Bar { $i }
-    }
-}
-
-mac_extern! {
-    fn foo();
-}
-mac_assoc! {
-    fn foo() {}
-}
diff --git a/src/test/ui/ast-json/ast-json-noexpand-output.rs b/src/test/ui/ast-json/ast-json-noexpand-output.rs
deleted file mode 100644
index cba539f0065..00000000000
--- a/src/test/ui/ast-json/ast-json-noexpand-output.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// Check that AST json printing works.
-#![crate_type = "lib"]
-
-// check-pass
-// compile-flags: -Zast-json-noexpand
-// normalize-stdout-test ":\d+" -> ":0"
-
-// Only include a single item to reduce how often the test output needs
-// updating.
-extern crate core;
diff --git a/src/test/ui/ast-json/ast-json-noexpand-output.stdout b/src/test/ui/ast-json/ast-json-noexpand-output.stdout
deleted file mode 100644
index 6f6e9b38e94..00000000000
--- a/src/test/ui/ast-json/ast-json-noexpand-output.stdout
+++ /dev/null
@@ -1 +0,0 @@
-{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"crate_type","span":{"lo":0,"hi":0}},"id":0,"args":null}],"tokens":null},"args":{"variant":"Eq","fields":[{"lo":0,"hi":0},{"variant":"Ast","fields":[{"id":0,"kind":{"variant":"Lit","fields":[{"token":{"kind":"Str","symbol":"lib","suffix":null},"kind":{"variant":"Str","fields":["lib","Cooked"]},"span":{"lo":0,"hi":0}}]},"span":{"lo":0,"hi":0},"attrs":{"0":null},"tokens":{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}}]}]},"tokens":null},{"0":[[{"variant":"Token","fields":[{"kind":"Pound","span":{"lo":0,"hi":0}}]},"Joint"],[{"variant":"Token","fields":[{"kind":"Not","span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Delimited","fields":[{"open":{"lo":0,"hi":0},"close":{"lo":0,"hi":0}},"Bracket",{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Ident","fields":["crate_type",false]},"span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Token","fields":[{"kind":"Eq","span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}]},"Alone"]]}]},"id":null,"style":"Inner","span":{"lo":0,"hi":0}}],"items":[{"attrs":[],"id":0,"span":{"lo":0,"hi":0},"vis":{"kind":"Inherited","span":{"lo":0,"hi":0},"tokens":null},"ident":{"name":"core","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null}],"spans":{"inner_span":{"lo":0,"hi":0},"inject_use_span":{"lo":0,"hi":0}},"id":0,"is_placeholder":false}
diff --git a/src/test/ui/ast-json/ast-json-output.rs b/src/test/ui/ast-json/ast-json-output.rs
deleted file mode 100644
index 2e009149ed6..00000000000
--- a/src/test/ui/ast-json/ast-json-output.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// Check that AST json printing works.
-#![crate_type = "lib"]
-
-// check-pass
-// compile-flags: -Zast-json
-// normalize-stdout-test ":\d+" -> ":0"
-
-// Only include a single item to reduce how often the test output needs
-// updating.
-extern crate core;
diff --git a/src/test/ui/ast-json/ast-json-output.stdout b/src/test/ui/ast-json/ast-json-output.stdout
deleted file mode 100644
index 5637ce596b3..00000000000
--- a/src/test/ui/ast-json/ast-json-output.stdout
+++ /dev/null
@@ -1 +0,0 @@
-{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"crate_type","span":{"lo":0,"hi":0}},"id":0,"args":null}],"tokens":null},"args":{"variant":"Eq","fields":[{"lo":0,"hi":0},{"variant":"Ast","fields":[{"id":0,"kind":{"variant":"Lit","fields":[{"token":{"kind":"Str","symbol":"lib","suffix":null},"kind":{"variant":"Str","fields":["lib","Cooked"]},"span":{"lo":0,"hi":0}}]},"span":{"lo":0,"hi":0},"attrs":{"0":null},"tokens":{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}}]}]},"tokens":null},{"0":[[{"variant":"Token","fields":[{"kind":"Pound","span":{"lo":0,"hi":0}}]},"Joint"],[{"variant":"Token","fields":[{"kind":"Not","span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Delimited","fields":[{"open":{"lo":0,"hi":0},"close":{"lo":0,"hi":0}},"Bracket",{"0":[[{"variant":"Token","fields":[{"kind":{"variant":"Ident","fields":["crate_type",false]},"span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Token","fields":[{"kind":"Eq","span":{"lo":0,"hi":0}}]},"Alone"],[{"variant":"Token","fields":[{"kind":{"variant":"Literal","fields":[{"kind":"Str","symbol":"lib","suffix":null}]},"span":{"lo":0,"hi":0}}]},"Alone"]]}]},"Alone"]]}]},"id":null,"style":"Inner","span":{"lo":0,"hi":0}}],"items":[{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"prelude_import","span":{"lo":0,"hi":0}},"id":0,"args":null}],"tokens":null},"args":"Empty","tokens":null},null]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"kind":"Inherited","span":{"lo":0,"hi":0},"tokens":null},"ident":{"name":"","span":{"lo":0,"hi":0}},"kind":{"variant":"Use","fields":[{"prefix":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"{{root}}","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"std","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"prelude","span":{"lo":0,"hi":0}},"id":0,"args":null},{"ident":{"name":"rust_2015","span":{"lo":0,"hi":0}},"id":0,"args":null}],"tokens":null},"kind":"Glob","span":{"lo":0,"hi":0}}]},"tokens":null},{"attrs":[{"kind":{"variant":"Normal","fields":[{"path":{"span":{"lo":0,"hi":0},"segments":[{"ident":{"name":"macro_use","span":{"lo":0,"hi":0}},"id":0,"args":null}],"tokens":null},"args":"Empty","tokens":null},null]},"id":null,"style":"Outer","span":{"lo":0,"hi":0}}],"id":0,"span":{"lo":0,"hi":0},"vis":{"kind":"Inherited","span":{"lo":0,"hi":0},"tokens":null},"ident":{"name":"std","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null},{"attrs":[],"id":0,"span":{"lo":0,"hi":0},"vis":{"kind":"Inherited","span":{"lo":0,"hi":0},"tokens":null},"ident":{"name":"core","span":{"lo":0,"hi":0}},"kind":{"variant":"ExternCrate","fields":[null]},"tokens":null}],"spans":{"inner_span":{"lo":0,"hi":0},"inject_use_span":{"lo":0,"hi":0}},"id":0,"is_placeholder":false}