Only colorize the profiler report when writing to a terminal

src/IRPrinter.cpp

@@ -561,7 +561,10 @@ IRPrinter::IRPrinter(ostream &s)
             int val = std::atoi(opt);
             use_colors = val != 0;
         } else {
-            use_colors = supports_ansi(stream);
+            // Respect NO_COLOR in addition to whether we're writing to a
+            // terminal, matching the profiler report's color gate.
+            const char *no_color = getenv("NO_COLOR");
+            use_colors = !(no_color && no_color[0]) && supports_ansi(stream);
         }
         if (use_colors) {
             ansi = true;

src/LLVM_Runtime_Linker.cpp

@@ -826,7 +826,7 @@ void add_underscore_to_posix_call(llvm::CallInst *call, llvm::Function *fn, llvm
  * of mcjit, so we just rewrite uses of these functions to include an
  * underscore. */
 void add_underscores_to_posix_calls_on_windows(llvm::Module *m) {
-    string posix_fns[] = {"vsnprintf", "open", "close", "write", "fileno"};
+    string posix_fns[] = {"vsnprintf", "open", "close", "write", "fileno", "isatty"};
 
     string *posix_fns_begin = posix_fns;
     string *posix_fns_end = posix_fns + sizeof(posix_fns) / sizeof(posix_fns[0]);

src/runtime/profiler_common.cpp

@@ -513,10 +513,24 @@ ALWAYS_INLINE bool counter_is_approximate(const halide_profiler_func_stats *fs,
 WEAK void halide_profiler_report_unlocked(void *user_context, halide_profiler_state *s) {
     StringStreamPrinter<1024> sstr(user_context);
 
-    bool support_colors = false;
-    const char *term = getenv("TERM");
-    if (term && (strstr(term, "color") || strstr(term, "xterm"))) {
-        support_colors = true;
+    // Decide whether to emit ANSI color escapes. HL_COLORS, if set, is an
+    // explicit override matching IRPrinter: "0" forces colors off, anything
+    // else on. Otherwise honor NO_COLOR and auto-detect a color-capable
+    // terminal. Checking TERM alone isn't enough: CI and other redirected
+    // environments often set TERM=xterm-256color while stdout is a pipe or
+    // file, which would splatter escape codes into the captured log. The
+    // report is printed via halide_print, whose default writes to stdout.
+    bool support_colors;
+    const char *hl_colors = getenv("HL_COLORS");
+    if (hl_colors) {
+        support_colors = atoi(hl_colors) != 0;
+    } else {
+        const char *no_color = getenv("NO_COLOR");
+        const char *term = getenv("TERM");
+        support_colors =
+            !(no_color && no_color[0]) &&
+            term && (strstr(term, "color") || strstr(term, "xterm")) &&
+            isatty(STDOUT_FILENO);
     }
 
     // Column-aligned rows are produced from `const char *` templates. A

src/runtime/runtime_internal.h

@@ -121,6 +121,7 @@ int fclose(void *);
 int close(int);
 size_t fwrite(const void *, size_t, size_t, void *);
 ssize_t write(int fd, const void *buf, size_t bytes);
+int isatty(int fd);
 int remove(const char *pathname);
 int ioctl(int fd, unsigned long request, ...);
 char *strncpy(char *dst, const char *src, size_t n);