Diagnostics: if a line is longer than 4096 characters, don't print it.

Specifically, don't print snippets, caret diagnostics, or ranges for
lines over 4096 characters. We copy the line around a few times in our
diagnostics machinery, and we have to print a caret line that's just as
long. This uses a lot of memory just to create a poor user experience as
we print out a line much too long for anyone to read...or spend extra
energy trying to fit it to -fmessage-length.

<rdar://problem/13106850>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173976 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 20 insertions, 2 deletions

diff --git a/lib/Frontend/TextDiagnostic.cpp b/lib/Frontend/TextDiagnostic.cpp
index f7c0d60ae4..c2562eb5fc 100644
--- a/lib/Frontend/TextDiagnostic.cpp
+++ b/lib/Frontend/TextDiagnostic.cpp
@@ -1096,18 +1096,26 @@ void TextDiagnostic::emitSnippetAndCaret(
 
   unsigned LineNo = SM.getLineNumber(FID, FileOffset);
   unsigned ColNo = SM.getColumnNumber(FID, FileOffset);
+  
+  // Arbitrarily stop showing snippets when the line is too long.
+  static const unsigned MaxLineLength = 4096;
+  if (ColNo > MaxLineLength)
+    return;
 
   // Rewind from the current position to the start of the line.
   const char *TokPtr = BufStart+FileOffset;
   const char *LineStart = TokPtr-ColNo+1; // Column # is 1-based.
 
-
   // Compute the line end.  Scan forward from the error position to the end of
   // the line.
   const char *LineEnd = TokPtr;
   while (*LineEnd != '\n' && *LineEnd != '\r' && *LineEnd != '\0')
     ++LineEnd;
 
+  // Arbitrarily stop showing snippets when the line is too long.
+  if (LineEnd - LineStart > MaxLineLength)
+    return;
+
   // Copy the line of code into an std::string for ease of manipulation.
   std::string SourceLine(LineStart, LineEnd);
 
diff --git a/test/Misc/diag-line-wrapping.cpp b/test/Misc/diag-line-wrapping.cpp
index 830aa13408..ea119afc64 100644
--- a/test/Misc/diag-line-wrapping.cpp
+++ b/test/Misc/diag-line-wrapping.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -fmessage-length 60 %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -fsyntax-only -fmessage-length 0 %s 2>&1 | FileCheck %s
 
 struct B { void f(); };
 struct D1 : B {};
@@ -10,4 +11,13 @@ struct DD : D1, D2 {
   // CHECK: {{.*}}: error:
   // CHECK: struct DD -> struct D1 -> struct B
   // CHECK: struct DD -> struct D2 -> struct B
-}
+};
+
+// A line longer than 4096 characters should cause us to suppress snippets no
+// matter what -fmessage-length is set to.
+#pragma clang diagnostic push
+#pragma clang diagnostic warning "-Wconversion"
+// CHECK: implicit conversion loses floating-point precision
+// CHECK-NOT: static const float numbers[]
+static const float numbers[] = {0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.3529411764705883,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.4117647058823529,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.4705882352941176,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.4117647058823529,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.4705882352941176,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.5294117647058824,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.4705882352941176,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.5294117647058824,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.5294117647058824,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.1764705882352941,0.3529411764705883,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.1764705882352941,0.4117647058823529,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2352941176470588,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2352941176470588,0.4117647058823529,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2352941176470588,0.4705882352941176,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2941176470588235,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2941176470588235,0.4705882352941176,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.2941176470588235,0.5294117647058824,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.3529411764705883,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.1764705882352941,0.3529411764705883,0.5294117647058824,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2352941176470588,0.1176470588235294,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2352941176470588,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2352941176470588,0.4117647058823529,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2941176470588235,0.1764705882352941,0.4117647058823529,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2941176470588235,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.2941176470588235,0.4705882352941176,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.3529411764705883,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.3529411764705883,0.5294117647058824,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2352941176470588,0.4117647058823529,0.2941176470588235,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.2941176470588235,0.1176470588235294,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.2941176470588235,0.1764705882352941,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.3529411764705883,0.1764705882352941,0.3529411764705883,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.3529411764705883,0.2352941176470588,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.4117647058823529,0.2352941176470588,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.2941176470588235,0.4705882352941176,0.2941176470588235,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.3529411764705883,0.1176470588235294,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.3529411764705883,0.1764705882352941,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.4117647058823529,0.1764705882352941,0.2941176470588235,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.4117647058823529,0.2352941176470588,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.4705882352941176,0.2352941176470588,0.2352941176470588,0.1176470588235294,0.1176470588235294,0.3529411764705883,0.5294117647058824,0.2941176470588235,0.1764705882352941,0.1176470588235294,0.1176470588235294,0.4117647058823529};
+#pragma clang diagnostic pop