Sep 04 05:31:51.902 INFO checking stainless-0.1.12 against master#2687112ea6a8701cbf36e6dd4d77d64694cf93d8 for pr-53913
Sep 04 05:31:51.902 INFO running: cargo +2687112ea6a8701cbf36e6dd4d77d64694cf93d8-alt check --frozen --all --all-targets
Sep 04 05:31:51.902 INFO running `"docker" "create" "-v" "/home/ec2-user/crater/./work/local/test-source/worker-0/pr-53913/master#2687112ea6a8701cbf36e6dd4d77d64694cf93d8:/source:ro,Z" "-v" "/home/ec2-user/crater/./work/local/target-dirs/pr-53913/worker-0/master#2687112ea6a8701cbf36e6dd4d77d64694cf93d8:/target:rw,Z" "-v" "/home/ec2-user/crater/./work/local/cargo-home:/cargo-home:ro,Z" "-v" "/home/ec2-user/crater/./work/local/rustup-home:/rustup-home:ro,Z" "-e" "USER_ID=500" "-e" "CMD=cargo +2687112ea6a8701cbf36e6dd4d77d64694cf93d8-alt check --frozen --all --all-targets" "-e" "CARGO_INCREMENTAL=0" "-e" "RUST_BACKTRACE=full" "-e" "RUSTFLAGS=--cap-lints=forbid" "-m" "2G" "crater"`
Sep 04 05:31:52.038 INFO blam! 184ae2842f17da98ec64c952c0dea8d7cc5cd9466073b23e16e288c2de5cf4b4
Sep 04 05:31:52.039 INFO running `"docker" "start" "-a" "184ae2842f17da98ec64c952c0dea8d7cc5cd9466073b23e16e288c2de5cf4b4"`
Sep 04 05:31:52.980 INFO kablam!    Compiling stainless v0.1.12 (file:///source)
Sep 04 05:31:55.416 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.416 INFO kablam!   --> src/describe.rs:31:19
Sep 04 05:31:55.416 INFO kablam!    |
Sep 04 05:31:55.416 INFO kablam! 31 | use syntax::{ast, codemap, parse, tokenstream};
Sep 04 05:31:55.416 INFO kablam!    |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.417 INFO kablam! 
Sep 04 05:31:55.417 INFO kablam! error[E0432]: unresolved import `syntax::util::small_vector`
Sep 04 05:31:55.417 INFO kablam!   --> src/describe.rs:34:19
Sep 04 05:31:55.417 INFO kablam!    |
Sep 04 05:31:55.417 INFO kablam! 34 | use syntax::util::small_vector::SmallVector;
Sep 04 05:31:55.417 INFO kablam!    |                   ^^^^^^^^^^^^ Could not find `small_vector` in `util`
Sep 04 05:31:55.417 INFO kablam! 
Sep 04 05:31:55.417 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.417 INFO kablam!  --> src/parse.rs:7:19
Sep 04 05:31:55.417 INFO kablam!   |
Sep 04 05:31:55.417 INFO kablam! 7 | use syntax::{ast, codemap};
Sep 04 05:31:55.417 INFO kablam!   |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.417 INFO kablam! 
Sep 04 05:31:55.418 INFO kablam! error[E0432]: unresolved import `syntax::abi`
Sep 04 05:31:55.418 INFO kablam!  --> src/generate.rs:9:19
Sep 04 05:31:55.418 INFO kablam!   |
Sep 04 05:31:55.418 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.418 INFO kablam!   |                   ^^^ no `abi` in the root
Sep 04 05:31:55.418 INFO kablam! 
Sep 04 05:31:55.418 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.418 INFO kablam!  --> src/generate.rs:9:24
Sep 04 05:31:55.418 INFO kablam!   |
Sep 04 05:31:55.418 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.418 INFO kablam!   |                        ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.418 INFO kablam! 
Sep 04 05:31:55.694 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:55.694 INFO kablam!    --> src/generate.rs:118:19
Sep 04 05:31:55.694 INFO kablam!     |
Sep 04 05:31:55.694 INFO kablam! 118 |               node: ast::ItemKind::Fn(
Sep 04 05:31:55.694 INFO kablam!     |  ___________________^
Sep 04 05:31:55.694 INFO kablam! 119 | |                 // Takes no arguments and returns ()
Sep 04 05:31:55.694 INFO kablam! 120 | |                 P(ast::FnDecl {
Sep 04 05:31:55.694 INFO kablam! 121 | |                     inputs: vec![],
Sep 04 05:31:55.694 INFO kablam! ...   |
Sep 04 05:31:55.694 INFO kablam! 132 | |                 test_body
Sep 04 05:31:55.695 INFO kablam! 133 | |             ),
Sep 04 05:31:55.695 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:55.695 INFO kablam! 
Sep 04 05:31:55.744 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.744 INFO kablam!   --> src/describe.rs:31:19
Sep 04 05:31:55.744 INFO kablam!    |
Sep 04 05:31:55.744 INFO kablam! 31 | use syntax::{ast, codemap, parse, tokenstream};
Sep 04 05:31:55.744 INFO kablam!    |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.744 INFO kablam! 
Sep 04 05:31:55.744 INFO kablam! error[E0432]: unresolved import `syntax::util::small_vector`
Sep 04 05:31:55.744 INFO kablam!   --> src/describe.rs:34:19
Sep 04 05:31:55.744 INFO kablam!    |
Sep 04 05:31:55.745 INFO kablam! 34 | use syntax::util::small_vector::SmallVector;
Sep 04 05:31:55.745 INFO kablam!    |                   ^^^^^^^^^^^^ Could not find `small_vector` in `util`
Sep 04 05:31:55.745 INFO kablam! 
Sep 04 05:31:55.745 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.745 INFO kablam!  --> src/parse.rs:7:19
Sep 04 05:31:55.745 INFO kablam!   |
Sep 04 05:31:55.745 INFO kablam! 7 | use syntax::{ast, codemap};
Sep 04 05:31:55.745 INFO kablam!   |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.745 INFO kablam! 
Sep 04 05:31:55.745 INFO kablam! error[E0432]: unresolved import `syntax::abi`
Sep 04 05:31:55.745 INFO kablam!  --> src/generate.rs:9:19
Sep 04 05:31:55.745 INFO kablam!   |
Sep 04 05:31:55.745 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.745 INFO kablam!   |                   ^^^ no `abi` in the root
Sep 04 05:31:55.745 INFO kablam! 
Sep 04 05:31:55.745 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.745 INFO kablam!  --> src/generate.rs:9:24
Sep 04 05:31:55.745 INFO kablam!   |
Sep 04 05:31:55.745 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.745 INFO kablam!   |                        ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.745 INFO kablam! 
Sep 04 05:31:55.808 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:55.809 INFO kablam!    --> src/generate.rs:135:18
Sep 04 05:31:55.809 INFO kablam!     |
Sep 04 05:31:55.809 INFO kablam! 135 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:55.809 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:55.809 INFO kablam! 
Sep 04 05:31:55.811 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:55.811 INFO kablam!    --> src/generate.rs:157:19
Sep 04 05:31:55.811 INFO kablam!     |
Sep 04 05:31:55.811 INFO kablam! 157 |               node: ast::ItemKind::Fn(
Sep 04 05:31:55.811 INFO kablam!     |  ___________________^
Sep 04 05:31:55.811 INFO kablam! 158 | |                 // Takes one argument of &mut Bencher
Sep 04 05:31:55.812 INFO kablam! 159 | |                 P(ast::FnDecl {
Sep 04 05:31:55.812 INFO kablam! 160 | |                     inputs: vec![ast::Arg {
Sep 04 05:31:55.812 INFO kablam! ...   |
Sep 04 05:31:55.812 INFO kablam! 176 | |                 block
Sep 04 05:31:55.812 INFO kablam! 177 | |             ),
Sep 04 05:31:55.812 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:55.812 INFO kablam! 
Sep 04 05:31:55.826 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:55.826 INFO kablam!    --> src/generate.rs:179:18
Sep 04 05:31:55.826 INFO kablam!     |
Sep 04 05:31:55.826 INFO kablam! 179 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:55.826 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:55.826 INFO kablam! 
Sep 04 05:31:55.845 INFO kablam! error[E0599]: no associated item named `Public` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:55.845 INFO kablam!    --> src/generate.rs:228:47
Sep 04 05:31:55.845 INFO kablam!     |
Sep 04 05:31:55.845 INFO kablam! 228 |         let super_glob = cx.item_use_glob(sp, ast::Visibility::Public, vec![cx.ident_of("super")]);
Sep 04 05:31:55.845 INFO kablam!     |                                               ^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:55.845 INFO kablam! 
Sep 04 05:31:55.856 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.856 INFO kablam!   --> src/describe.rs:31:19
Sep 04 05:31:55.856 INFO kablam!    |
Sep 04 05:31:55.856 INFO kablam! 31 | use syntax::{ast, codemap, parse, tokenstream};
Sep 04 05:31:55.856 INFO kablam!    |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.856 INFO kablam! 
Sep 04 05:31:55.856 INFO kablam! error[E0432]: unresolved import `syntax::util::small_vector`
Sep 04 05:31:55.857 INFO kablam!   --> src/describe.rs:34:19
Sep 04 05:31:55.857 INFO kablam!    |
Sep 04 05:31:55.857 INFO kablam! 34 | use syntax::util::small_vector::SmallVector;
Sep 04 05:31:55.857 INFO kablam!    |                   ^^^^^^^^^^^^ Could not find `small_vector` in `util`
Sep 04 05:31:55.857 INFO kablam! 
Sep 04 05:31:55.857 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.857 INFO kablam!  --> src/parse.rs:7:19
Sep 04 05:31:55.857 INFO kablam!   |
Sep 04 05:31:55.857 INFO kablam! 7 | use syntax::{ast, codemap};
Sep 04 05:31:55.857 INFO kablam!   |                   ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.857 INFO kablam! 
Sep 04 05:31:55.857 INFO kablam! error[E0432]: unresolved import `syntax::abi`
Sep 04 05:31:55.857 INFO kablam!  --> src/generate.rs:9:19
Sep 04 05:31:55.857 INFO kablam!   |
Sep 04 05:31:55.857 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.857 INFO kablam!   |                   ^^^ no `abi` in the root
Sep 04 05:31:55.857 INFO kablam! 
Sep 04 05:31:55.857 INFO kablam! error[E0432]: unresolved import `syntax::codemap`
Sep 04 05:31:55.857 INFO kablam!  --> src/generate.rs:9:24
Sep 04 05:31:55.857 INFO kablam!   |
Sep 04 05:31:55.857 INFO kablam! 9 | use syntax::{ast, abi, codemap};
Sep 04 05:31:55.857 INFO kablam!   |                        ^^^^^^^ no `codemap` in the root
Sep 04 05:31:55.857 INFO kablam! 
Sep 04 05:31:55.861 INFO kablam! error: aborting due to 10 previous errors
Sep 04 05:31:55.861 INFO kablam! 
Sep 04 05:31:55.861 INFO kablam! Some errors occurred: E0061, E0432, E0599.
Sep 04 05:31:55.861 INFO kablam! For more information about an error, try `rustc --explain E0061`.
Sep 04 05:31:55.876 INFO kablam! error: Could not compile `stainless`.
Sep 04 05:31:55.876 INFO kablam! warning: build failed, waiting for other jobs to finish...
Sep 04 05:31:56.083 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:56.083 INFO kablam!    --> src/generate.rs:118:19
Sep 04 05:31:56.083 INFO kablam!     |
Sep 04 05:31:56.083 INFO kablam! 118 |               node: ast::ItemKind::Fn(
Sep 04 05:31:56.083 INFO kablam!     |  ___________________^
Sep 04 05:31:56.083 INFO kablam! 119 | |                 // Takes no arguments and returns ()
Sep 04 05:31:56.084 INFO kablam! 120 | |                 P(ast::FnDecl {
Sep 04 05:31:56.084 INFO kablam! 121 | |                     inputs: vec![],
Sep 04 05:31:56.084 INFO kablam! ...   |
Sep 04 05:31:56.084 INFO kablam! 132 | |                 test_body
Sep 04 05:31:56.084 INFO kablam! 133 | |             ),
Sep 04 05:31:56.084 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:56.084 INFO kablam! 
Sep 04 05:31:56.088 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:56.088 INFO kablam!    --> src/generate.rs:118:19
Sep 04 05:31:56.088 INFO kablam!     |
Sep 04 05:31:56.088 INFO kablam! 118 |               node: ast::ItemKind::Fn(
Sep 04 05:31:56.088 INFO kablam!     |  ___________________^
Sep 04 05:31:56.088 INFO kablam! 119 | |                 // Takes no arguments and returns ()
Sep 04 05:31:56.088 INFO kablam! 120 | |                 P(ast::FnDecl {
Sep 04 05:31:56.088 INFO kablam! 121 | |                     inputs: vec![],
Sep 04 05:31:56.089 INFO kablam! ...   |
Sep 04 05:31:56.089 INFO kablam! 132 | |                 test_body
Sep 04 05:31:56.089 INFO kablam! 133 | |             ),
Sep 04 05:31:56.089 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:56.089 INFO kablam! 
Sep 04 05:31:56.174 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.174 INFO kablam!    --> src/generate.rs:135:18
Sep 04 05:31:56.174 INFO kablam!     |
Sep 04 05:31:56.175 INFO kablam! 135 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:56.175 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.175 INFO kablam! 
Sep 04 05:31:56.178 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:56.178 INFO kablam!    --> src/generate.rs:157:19
Sep 04 05:31:56.178 INFO kablam!     |
Sep 04 05:31:56.178 INFO kablam! 157 |               node: ast::ItemKind::Fn(
Sep 04 05:31:56.178 INFO kablam!     |  ___________________^
Sep 04 05:31:56.178 INFO kablam! 158 | |                 // Takes one argument of &mut Bencher
Sep 04 05:31:56.178 INFO kablam! 159 | |                 P(ast::FnDecl {
Sep 04 05:31:56.178 INFO kablam! 160 | |                     inputs: vec![ast::Arg {
Sep 04 05:31:56.178 INFO kablam! ...   |
Sep 04 05:31:56.178 INFO kablam! 176 | |                 block
Sep 04 05:31:56.178 INFO kablam! 177 | |             ),
Sep 04 05:31:56.178 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:56.178 INFO kablam! 
Sep 04 05:31:56.195 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.195 INFO kablam!    --> src/generate.rs:179:18
Sep 04 05:31:56.195 INFO kablam!     |
Sep 04 05:31:56.195 INFO kablam! 179 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:56.195 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.195 INFO kablam! 
Sep 04 05:31:56.197 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.197 INFO kablam!    --> src/generate.rs:135:18
Sep 04 05:31:56.197 INFO kablam!     |
Sep 04 05:31:56.197 INFO kablam! 135 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:56.197 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.197 INFO kablam! 
Sep 04 05:31:56.200 INFO kablam! error[E0061]: this function takes 4 parameters but 6 parameters were supplied
Sep 04 05:31:56.200 INFO kablam!    --> src/generate.rs:157:19
Sep 04 05:31:56.200 INFO kablam!     |
Sep 04 05:31:56.200 INFO kablam! 157 |               node: ast::ItemKind::Fn(
Sep 04 05:31:56.200 INFO kablam!     |  ___________________^
Sep 04 05:31:56.200 INFO kablam! 158 | |                 // Takes one argument of &mut Bencher
Sep 04 05:31:56.200 INFO kablam! 159 | |                 P(ast::FnDecl {
Sep 04 05:31:56.200 INFO kablam! 160 | |                     inputs: vec![ast::Arg {
Sep 04 05:31:56.200 INFO kablam! ...   |
Sep 04 05:31:56.200 INFO kablam! 176 | |                 block
Sep 04 05:31:56.200 INFO kablam! 177 | |             ),
Sep 04 05:31:56.201 INFO kablam!     | |_____________^ expected 4 parameters
Sep 04 05:31:56.201 INFO kablam! 
Sep 04 05:31:56.218 INFO kablam! error[E0599]: no associated item named `Inherited` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.218 INFO kablam!    --> src/generate.rs:179:18
Sep 04 05:31:56.218 INFO kablam!     |
Sep 04 05:31:56.218 INFO kablam! 179 |             vis: ast::Visibility::Inherited,
Sep 04 05:31:56.218 INFO kablam!     |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.218 INFO kablam! 
Sep 04 05:31:56.222 INFO kablam! error[E0599]: no associated item named `Public` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.224 INFO kablam!    --> src/generate.rs:228:47
Sep 04 05:31:56.224 INFO kablam!     |
Sep 04 05:31:56.224 INFO kablam! 228 |         let super_glob = cx.item_use_glob(sp, ast::Visibility::Public, vec![cx.ident_of("super")]);
Sep 04 05:31:56.225 INFO kablam!     |                                               ^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.225 INFO kablam! 
Sep 04 05:31:56.234 INFO kablam! error[E0599]: no associated item named `Public` found for type `syntax::source_map::Spanned<syntax::ast::VisibilityKind>` in the current scope
Sep 04 05:31:56.234 INFO kablam!    --> src/generate.rs:228:47
Sep 04 05:31:56.234 INFO kablam!     |
Sep 04 05:31:56.234 INFO kablam! 228 |         let super_glob = cx.item_use_glob(sp, ast::Visibility::Public, vec![cx.ident_of("super")]);
Sep 04 05:31:56.234 INFO kablam!     |                                               ^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `syntax::source_map::Spanned<syntax::ast::VisibilityKind>`
Sep 04 05:31:56.234 INFO kablam! 
Sep 04 05:31:56.242 INFO kablam! error: aborting due to 10 previous errors
Sep 04 05:31:56.242 INFO kablam! 
Sep 04 05:31:56.242 INFO kablam! Some errors occurred: E0061, E0432, E0599.
Sep 04 05:31:56.242 INFO kablam! For more information about an error, try `rustc --explain E0061`.
Sep 04 05:31:56.247 INFO kablam! error: aborting due to 10 previous errors
Sep 04 05:31:56.247 INFO kablam! 
Sep 04 05:31:56.247 INFO kablam! Some errors occurred: E0061, E0432, E0599.
Sep 04 05:31:56.247 INFO kablam! For more information about an error, try `rustc --explain E0061`.
Sep 04 05:31:56.255 INFO kablam! error: Could not compile `stainless`.
Sep 04 05:31:56.255 INFO kablam! warning: build failed, waiting for other jobs to finish...
Sep 04 05:31:56.262 INFO kablam! error: Could not compile `stainless`.
Sep 04 05:31:56.263 INFO kablam! 
Sep 04 05:31:56.263 INFO kablam! To learn more, run the command again with --verbose.
Sep 04 05:31:56.263 INFO kablam! su: No module specific data is present
Sep 04 05:31:56.806 INFO running `"docker" "rm" "-f" "184ae2842f17da98ec64c952c0dea8d7cc5cd9466073b23e16e288c2de5cf4b4"`
Sep 04 05:31:56.903 INFO blam! 184ae2842f17da98ec64c952c0dea8d7cc5cd9466073b23e16e288c2de5cf4b4