#10021: Add "Error:" prefix for compile-time error messages -------------------------------------+------------------------------------- Reporter: k-bx | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by spl): * cc: sean.leather@… (added) Old description:
The proposal is to modify GHC compile-time output for error-messages, by adding a prefix, similar to what we currently have for warnings.
An example of a warning message (see `Warning:` prefix):
{{{ ➜ cat test.hs main = putStrLn "Hello!" ➜ ghc --make -fforce-recomp -Wall ./test.hs [1 of 1] Compiling Main ( test.hs, test.o )
test.hs:1:1: Warning: Top-level binding with no type signature: main :: IO () Linking test ... }}}
An example of current output for an error:
{{{ ➜ cat test2.hs main = foo ➜ ghc --make -fforce-recomp -Wall ./test2.hs [1 of 1] Compiling Main ( test2.hs, test2.o )
test2.hs:1:8: Not in scope: ‘foo’ }}}
The proposal is to change it to become:
{{{ ➜ cat test2.hs main = foo ➜ ghc --make -fforce-recomp -Wall ./test2.hs [1 of 1] Compiling Main ( test2.hs, test2.o )
test2.hs:1:8: Error: Not in scope: ‘foo’ }}}
This proposal only affects error messages produced by GHC itself. For example, the behaviour of the `error` function is unaffected.
== Motivation ==
Main motivation point right now is that there's a ticket #9219 (parallel build's output of errors doesn't occur at the end of output), due to which, error-reporting of your program might get lost somewhere in the middle of a build-log. As another example, if your program has a lot of warnings, and you build it with multiple cores, you almost always get an error lost somewhere in the middle of warnings and it's almost impossible to find.
So, this feature's main purpose is to ease navigation in textual output of ghc in order to find errors quickly, not being tied to output ordering.
== Disadvantages ==
Many regression tests might need a fix.
== Additional consideration ==
@hvr proposed that during work on this bug we could make GHC output more consistent with other compiler's (GCC and clang) by also lower-casing "Error" and "Warning" prefixes.
This might be potentially useful for existing tools that work on top of compiler output for finding errors/warning, and GHC's output will become "more valid" for them.
New description: We propose adding the prefix `Error:` to compile-time error messages produced by GHC. An example of a warning message (see `Warning:` prefix): {{{ ➜ cat test.hs main = putStrLn "Hello!" ➜ ghc --make -fforce-recomp -Wall ./test.hs [1 of 1] Compiling Main ( test.hs, test.o ) test.hs:1:1: Warning: Top-level binding with no type signature: main :: IO () Linking test ... }}} An example of a current error message: {{{ ➜ cat test2.hs main = foo ➜ ghc --make -fforce-recomp -Wall ./test2.hs [1 of 1] Compiling Main ( test2.hs, test2.o ) test2.hs:1:8: Not in scope: ‘foo’ }}} The proposal is to change the error message to become: {{{ ➜ cat test2.hs main = foo ➜ ghc --make -fforce-recomp -Wall ./test2.hs [1 of 1] Compiling Main ( test2.hs, test2.o ) test2.hs:1:8: Error: Not in scope: ‘foo’ }}} This change affects only the error messages produced by GHC when compiling. It does not change runtime error reporting, e.g. with the `error` function. == Motivation == We wish to make compile-time error messages easier for humans and computers to identify. For example, when running a long parallel build, it can be easy to miss an error message (see #9219 for an example). With a known string such as `Error:`, we can use search functionality in a terminal window or text editor (when viewing the build log) or use a command-line tool such as `grep` (when streaming and filtering the build log) to quickly find errors. As a secondary motivation, adding `Error:` for error messages brings a nice symmetry to the current use of `Warning:` for warning messages. == Disadvantages == The output of many regression tests will need to be updated for the new error message format. == Additional consideration == @hvr proposed that during work on this bug we could make GHC output more consistent with other compiler's (GCC and clang) by also lower-casing "Error" and "Warning" prefixes. This might be potentially useful for existing tools that work on top of compiler output for finding errors/warning, and GHC's output will become "more valid" for them. -- Comment: I modified the ticket description in an attempt to be more clear about the proposal and to expand the motivation. P.S. I'm heavily in favor of this. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10021#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler