From dd5089060e8a57078e771bde1c02b15ab0d28281 Mon Sep 17 00:00:00 2001
From: Sebastian Wilzbach <seb@wilzba.ch>
Date: Wed, 11 Jul 2018 06:38:05 +0200
Subject: [PATCH] Generate expressive diagnostic messages

---
 changelog/error-pretty.dd                  | 21 +++++++++++++++
 src/dmd/cli.d                              |  3 +++
 src/dmd/errors.d                           | 30 ++++++++++++++++++++++
 src/dmd/globals.d                          |  1 +
 src/dmd/mars.d                             |  4 +++
 test/fail_compilation/fail_pretty_errors.d | 15 +++++++++++
 6 files changed, 74 insertions(+)
 create mode 100644 changelog/error-pretty.dd
 create mode 100644 test/fail_compilation/fail_pretty_errors.d

diff --git a/changelog/error-pretty.dd b/changelog/error-pretty.dd
new file mode 100644
index 000000000000..3fe7c21a662c
--- /dev/null
+++ b/changelog/error-pretty.dd
@@ -0,0 +1,21 @@
+dmd now supports expressive diagnostic error messages with `-verrors=pretty`
+
+With the new CLI option `-verrors=pretty` dmd will now show the offending line directly in its error messages.
+Consider this faulty program `test.d`:
+
+---
+void foo()
+{
+
+    a = 1;
+}
+---
+
+Now run it with `-verrors=pretty`:
+
+$(CONSOLE
+> dmd -verrors=pretty test.d
+ee.d(5): $(RED Error): undefined identifier a
+    a = 1;
+    ^
+)
diff --git a/src/dmd/cli.d b/src/dmd/cli.d
index 12030092a02e..91fc9eeb2b6f 100644
--- a/src/dmd/cli.d
+++ b/src/dmd/cli.d
@@ -553,6 +553,9 @@ dmd -cov -unittest myprog.d
         Option("verrors=spec",
             "show errors from speculative compiles such as __traits(compiles,...)"
         ),
+        Option("verrors=pretty",
+            "Pretty-print error messages with annotation of the erroring source line"
+        ),
         Option("-version",
             "print compiler version and exit"
         ),
diff --git a/src/dmd/errors.d b/src/dmd/errors.d
index 0c7c4fe9604d..2b654f6049b7 100644
--- a/src/dmd/errors.d
+++ b/src/dmd/errors.d
@@ -236,6 +236,36 @@ private void verrorPrint(const ref Loc loc, Color headerColor, const(char)* head
     else
         fputs(tmp.peekString(), stderr);
     fputc('\n', stderr);
+
+    if (global.params.prettyPrintErrors)
+    {
+        auto fp = fopen(loc.filename, "r");
+        scope(exit) fclose(fp);
+
+        if (fp)
+        {
+            char* lineptr;
+            ulong n = 1024;
+            import core.sys.posix.stdio;
+            foreach (_; 0 .. loc.linnum)
+            {
+                assert(getline(&lineptr, &n, fp) > 0);
+                if (lineptr is null)
+                    goto end;
+            }
+            if (lineptr is null)
+                goto end;
+            fprintf(stderr, "%s", lineptr);
+
+            if (loc.charnum >= 1)
+            foreach (_; 1 .. loc.charnum)
+                fputc(' ', stderr);
+
+            fputc('^', stderr);
+        }
+        fputc('\n', stderr);
+    }
+end:
     fflush(stderr);     // ensure it gets written out in case of compiler aborts
 }
 
diff --git a/src/dmd/globals.d b/src/dmd/globals.d
index 4d4a4481507c..8dc0aeb624cc 100644
--- a/src/dmd/globals.d
+++ b/src/dmd/globals.d
@@ -158,6 +158,7 @@ struct Param
      */
 
     bool showGaggedErrors;  // print gagged errors anyway
+    bool prettyPrintErrors; // pretty print errors with the actual line
     bool manual;            // open browser on compiler manual
     bool usage;             // print usage and exit
     bool mcpuUsage;         // print help on -mcpu switch
diff --git a/src/dmd/mars.d b/src/dmd/mars.d
index 0f8e977be63f..c7d8814d50c4 100644
--- a/src/dmd/mars.d
+++ b/src/dmd/mars.d
@@ -1732,6 +1732,10 @@ private bool parseCommandLine(const ref Strings arguments, const size_t argc, re
                 {
                     params.showGaggedErrors = true;
                 }
+                else if (startsWith(p + 9, "pretty"))
+                {
+                    params.prettyPrintErrors = true;
+                }
                 else
                     goto Lerror;
             }
diff --git a/test/fail_compilation/fail_pretty_errors.d b/test/fail_compilation/fail_pretty_errors.d
new file mode 100644
index 000000000000..cffd784ab4f2
--- /dev/null
+++ b/test/fail_compilation/fail_pretty_errors.d
@@ -0,0 +1,15 @@
+/*
+REQUIRED_ARGS: -verrors=pretty
+TEST_OUTPUT:
+---
+fail_compilation/fail_pretty_errors.d(14): Error: undefined identifier `a`
+    a = 1;
+    ^
+---
+*/
+
+void foo()
+{
+
+    a = 1;
+}